Biomass Roofing Skat

8/10/2019 Biomass Roofing Skat

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The Basics of

Biomass Roofing


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A uthor: N icolas H allInterm ed iate Tec hnolog y D evelop m ent G roup

A dd itiona l R esearch: S um ita S inha

Ed iting C om m ittee: K arl W ehrle, SK ATH eini M ller, A p roC on

D aniel S chw itter, S K AT

Illustratio ns: M atthew W hitton

First ed ition: 1997 b y S K AT

P ub lish er: S w iss C e ntre fo r D e ve lo pm e nt C o op era tio n

in Technolog y and M anag em ent (SK AT)

C H -90 00 S t.G allen , S w itzerlan d

D istributor: Interm ediate Technology P ublications (it),

103-105 S outham pton R ow

London W C 1B 4H H , England

E -m ail: itp ub s@ g n.ap c.org

Fax: + 44 171 436 2013

IS B N : 3-908001-73-0


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CONTENTS

Introduction ...........................................................................................1

G rass thatch .........................................................................................5

Palm thatch ...........................................................................................9

W ood tiles (shing les and shakes) .................................................. 13

R oof sheets w ith organic fib res ...................................................... 18

Treatm ent of b iom ass m aterials: p reserva tion ............................... 22

Fire p rotection ................................................................................... 25

Sources of further inform ation ......................................................... 27

K ey questions .................................................................................... 29

R ecom m end ations ............................................................................. 30

B A S IN ................................................................................................. 31


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The Basics of Biomass Roofing 1

Fundamental informationTh is b oo ks offers b as ic inform ation ab ou t roo fco veringusing p lan ts, or b iom ass m aterial. Th e b oo k foc uses p ar-ticu larly on tha tch a nd w ood tiles, but also co vers indus-trially-produced roofing m aterial that include a significantp rop ortion of biom ass m aterial.

In this b ook you w ill find inform ation ab out the ad van-tag es an d d isad van tag es of sp ec ific m aterials and tech-niq ues, basic inform ation a bout m aterials, skills, p erform -an ce an d co st. Th ere a re ad d resses and literature listsfor further inform ation and to ob tain m ore detailed tech-nical inform ation.

A time-honoured technologyH istorically, peo p le in alm ost every p art of the w orld ha ve

d ep en d ed on loc al m aterials for b uild ing . A nd for them ost exp ose d e lem en t the roo f p lan ts w ere usua llythe on ly loc al resou rce tha t co uld be turned into a dura-b le a nd w eathertight cove ring . The result is a rich h erit-ag e of roo fing tec hn ique an d architec tural tec hn olog y.

Tod ay, a rud im en tary tha tch rem ains the on ly op tion forp oo r rural co m m un ities in m ost develop ing co un tries. Incontrast, m any w ea lthy p eop le in E urop e ch oo se to liveunder a m eticu lously m an icu red ree d tha tch or perha ps,in N . A m erica, a roof of tim ber sh ing les.

Introduction

Revaluing the vernacularTh e va st array of very d ifferen t w ays to use p lan ts forroofing reflects the d ive rsity o f need , culture, econom yand environ m ent. S im p le m etho d s use u np rocessed d riedlea ves tied to a rou g h roo f fram e. Suc h a tha tch m ay o nlylast a year. O thers rely on careful cultiva tion of se lectedsp ec ies an d highly skilled craftsm an ship or com p lica tedind ustrial p roc esses an d are as d urab le as ston e, co n-

crete or fired clay tiles.

A ltho ug h m an y trad ition al tec hn iq ue s are b eing ab an -done d a s resou rce s be com e scarce a nd as attitud es andasp irations ch ange, othe rs a re s till b eing refined and newtec hn iq ue s are c on stan tly b eing d evelop ed . Inc rea singaw aren ess o f the urgen t ne ed to ration g lob al consu m p -tion of no n-ren ew ab le resou rce s is p lac ing g rea ter em -phasis on ren ew ab le m aterials.

In the Philip p ines the skill of creating a w atertig ht rooffrom sp lit b am b oo s is in d ec lining d em and . B am boo isno t so p lentiful and m any p refer a roof of iron she ets orM C R tiles . O n the othe r ha nd , w ater ree d tha tch is sopop ular in northern E urop e that there is a thriving inter-na tion al m arket for the b est ree d s and full em p loym en tfor skilled thatchers.

Modern roofingR e-ap p raisa l of trad ition al b uild ing tech niques and d evel-op m en t of ne w m etho d s to u se p lan ts for roo fing is ap arallel p roc es s. P lan t fib res, w ood chip s and g rass

stem s a s w ell as the organ ic b y-p rod uc ts o f m anufac tur-ing ind ustry an d food p rocessing are now the raw m ate-rial for an exp an d ing m arket for org an ic b ased roofingp rod uc ts. M ea nw hile, ch em ists an d en g ine ers a re re-Shingles are an attractive modern roofing material

Reed thatch such as in England lasts more than 60years


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The Basics of Biomass Roofing2

search ing m etho ds to p reserve an d firep roo f shing les andtha tch to m ee t inc rea sing ly string en t p erform an ce an dsafety stan d ards.

Types of materialsH un d red s of p lan t m aterials a re used for roo fing . A sim -p le classification d ivides them into three m ain typ es.

ThatchD ried g rasses or leave s, p laced up to 3 00m m thick a ndsecu red to a roo f b y lashing , w ea ving or na iling .

1. R ig id stem g rasses p rod uce the m ost durab le roo fs;up to 7 0 yea rs in tem perate c lim ates or 30 yea rs inthe trop ics. B oth a qua tic reeds an d sava nn ah g rasse sup to 15 00m m long b y 15m m diam eter are suitab le.Th ey ne ed ca reful cu ltivation an d p roc ess ing an dhig hly skilled tha tch ers to a ch ieve m axim um d urab il-ity.

2. Palm lea ves, soft-stem g rasse s and large tree lea vesrarely last m ore than 1 0 years and are frequently re-new ed w ithin 2 yea rs. There a re m any d ifferen t m eth-od s of p rocessing an d laying the se m aterials dep en d -ing on the characteristics of the m aterial, the type ofb uild ing an d its loc ation . C oc on ut lea ves a re usedthrou ghout the coas tal trop ics; various tec hniques arecom m on p rod uc ing a c overing tha t can last up to 1 2yea rs b ut usu ally no m ore tha n 2 yea rs.

ShinglesW oo d en or ba m b oo tiles tha t are eithe r saw n o r sp lit fromb locks of unse ason ed tim b er. H ardw ood sp ec ies are m ostd urab le, b ut an y straight g raine d w ood ca n b e used .

1. S hing les (saw n tiles ) and shakes (sp lit tiles) are up to600m m long, 400m m w ide and 20m m thick. They arena iled in asce nd ing layers to m ake a co vering 3 tilesthick. D ep en d ing on sp ec ies, the an g le of the roo f,clim ate an d w he the r trea ted w ith p reservatives. Th eyshou ld last at lea st 20 years. O ffcu ts from w aste w oo dcan b e used bu t m ay not be d urab le.

2. B am b oo cu lm s, sp lit to h alf-round s and laid as S pan -ish tiles a re c om m only used in reg ions w he re b am b oog row s. M ost co m m on ly used as tiles, lon g len g ths aresom etim es use d a nd this prod uc es a c on sid erab le

saving in sup p orting tim b erw ork. C he m ica l p rese rva-tives can extend the roof life up to 10 years.

Roof sheets and tilesInd ustrially p roduced sheets or tiles, either reinforced w ithor m ad e p red om ina ntly o f na tural fib res, w oo d -ch ip s o rorg an ic w astes.

1. Fib res o r p lan t resid ues are sp un or com p ressed to-g ethe r to m ake a flat shee t w hich is the n im p reg na tedw ith a b ind er. Va riou s p roc esse s a re use d . S om ehig hly m ec ha nised fac tories p rod uc e she ets con tinu -ou sly, othe rs use slow er m ore lab ou r inten sive m eth-od s. The m ost durab le shee ts ca n last m ore tha n 15


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ye ars b ut rigorous q uality c ontrol is vital. The sheetsne ed sealing w ith a w aterproo f paint un less the b ind er

is itse lf w aterp roof (e.g . b itum en).2. C em en t or resin shee ts or tiles reinforced w ith straw ,

g rass o r fib res to red uc e b rittlen ess a nd cracking .D ozen s o f d ifferen t p lan ts have bee n tested ; very feware com m ercially use d . Sheets m ay last 30 or m oreyears.

Technique Material Lifespan (years)

Thatch

P re fab ricated thatch panel C oconut leaf cocos nucifera 12 (Ind ia)

up to 8 (East A frica )

N ip a p alm le af n ip a fru tic an s up to 10 (P hillip in es)

R ig id stem thatch W ater R eed p hrag m ites australis 60+ (N orthern Europe)

R ig id stem thatch W heat straw 30 (Eng land )

S oft stem thatch R ice straw 6 (B ang ladesh)

Shingles

S p lit w ood tiles - shake W hite cheesew ood alstonia scholaris 30 (P ap ua N ew G uinea)

S p lit w ood shake W estern R ed ced ar thuja p licata up to 80 (N . A m erica)

Roof sheetsC o m p ressed corrug ated sheets, B ag asse (sug ar), coir, w o od chip s, up to 30 (W orld -w id e)

su rfa ce se ale d w ith b itu m en p aint o r h em p fib re

Techniques, materials and typical lifespan


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Roof typesO rg an ic m aterials d ec ay in w arm , w et co nd ition s, so

steep ly slop ing roofs w hich a llow w ater to d rain rap id lyare m ost d urab le. Th is m ea ns tha t the se m aterials a reb est suited to sm all- an d m ed ium -span build ing s. Span sw id er tha n 5m req uire lon g len g ths of rafter tim ber andca refully designed b rac ing system s.

Roof pitchIn g eneral, the low er the p erm eab ility of the m aterial theless slop e is req uired . Eac h m aterial ha s a n ap p rop riatem inim um ang le:

G rass or palm thatch 1:1 (45)

Wood Tilestreated sing les 1:1.5 (33)untreated shing les 1:1 (45)shakes 1:1 (45)

Fibre reinforced tilesP lain or S panish tiles 1:1.5 (33)R om an type 1:2 (26)Fib re reinforced sheets 1:3 (18)

Roof structuresR oo f struc tures for tha tch an d sh ing les do n ot ha ve to b ep erfectly leve l as the m aterial w ill m ould itse lf to irregu-larities that m ay occur if pole tim ber or sp lit w ood struc-tures are u sed . Thatch w orks w ell on cu rved or con ica lroo fs. C ha ng es of slop e w ithin a roo f or co m p lica tedroofs w hich include va lleys or roof w indow s a re liab le tocau se p rem ature d eca y and leaks.

WeightW eight: Th e h eaviest tha tch , w he n w et, w eig hs a pp roxi-

m ately 40kg /m 2, ab ou t the sam e a s con crete tiles . O the rthatch m aterials ten d to b e lig hter so nee d a less stron groo f struc ture. W oo d tiles vary b etw ee n 20 to 3 0kg /m 2.

VentilationVentilation: to a llow rap id d rying of the roof cove ring ,orga nic m aterials sh ou ld p referab ly b e laid on b atten snailed to rafters. U nd erlay or sarking should not b e nec-essa ry a nd w ill hind er ventilation . C lose b oa rd ing ove rrafters should b e avoided .

Key questions and answersQ D o sn akes and insects live in g rass or w ood roofs?

A M ayb e, bu t m ost m od ern h ouses h ave a ceiling w hichw ill stop insec ts and dust.

Q O rganic m aterials rot. W ont m y roo f rot?

A Ye s, but if it is d one w ell it sh ould last 70 ye ars (in a

tem p erate clim ate) or 30 years in the hu m id trop ics.H ow doe s tha t co m p are w ith a co rrug ated iron roo f inyo ur locality?

Q W ill m y tha tched roof burn?

A Yes, b ut a w ell tha tch ed roo f is like a b oo k pap ercatches fire easily b ut b ooks are hard to lig ht. Yo um ay n ot b e a llow ed to tha tch in a n u rban area , an dreg ulation s m ay m ea n tha t p ub lic b uild ing s can no t betha tch ed .

Checklist of benefits and problems

Potentials

Biomass material roofs:U se loc al, ren ew ab le m aterials.A re m ostly lab our intensive .

B lend w ith the e nvironm en t. Loo k very attractive .

C an b e very inexpensive.C an last up to 7 0 ye ars.

A re g ood sound and the rm al insu lation .C an ea sily b e rep aired .D ecay to com post w hen w orn out.A re bes t su ited for sm all build ing s.

Limits

Plant roofing materials:A re com bustib le.D ecay w hen w et.N eed steep roof slop es.A re he avier tha n co rrug ated iron .M ay no t b e ea sy to c ollec t rainw ater.M ay h ave c urren t value as fue l or fod d er.

N eed m ed ium to h igh skill.A re lab ou r inten sive to p roc ess and use .Th atch an d shing les a re n ot stan d ard p rod uc ts eachroo f w ill vary slightly.


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Grass thatch

or 0.8 hec tares o f w heat. Th us it is a p p arent that a thriv-ing thatching ind ustry can offer a valuab le m arke t for lo-ca l ag ricultural p roduce.

In m any cou ntries trad ition al tha tch ing g rasse s a re b e-com ing m ore a nd m ore sca rce, usually b ecau se land hasg rea ter value for othe r p rod uc ts. H ow ever, w he re tha tchha s be en p op ularly ac ce p ted , ind ig en ou s spe cies o fgrass can b e m anag ed profitab ly. M od ern hu sban dry m ayinclud e artificial control of w ater leve ls, in the case ofm arsh ree d s, rig orous w ee d ing , irrig ation an d se lec tiveap p lication o f fertilise r; althoug h recent rese arch in E u-rop e show s tha t excessive use of nitrog enous fertilise rca n p rod uc e hig he r yield s a t the exp en se of q ua lity.S traw and reed g row n und er this reg im e app ea rs to b ep rone to rap id dec ay cau sed b y fungal g row th.

Cultivation, harvesting and processing.Marsh reed (phragmites australis)

G row s in b oth tem perate and trop ica l clim ates. H arvested

after see d ha s m atured an d w he n fine lea ves ha vestarted to d ry. O p tim um size is 1 .8m lon g , tap ering stemand d iam eter 10m m . S hou ld preferab ly g row in a b out0.5m . dep th of w ater w hich is d raine d just b efore harvest-ing . To take a d vantag e o f the m ost d urab le p art of theree d stem tha t w hich g row s un d er w ater it should b ecu t as close to the g rou nd as possib le.

Th e s tem s, w ith the cu t ends a lig ned , are loosely tied insm all b und les an d c om b ed to rem ove d eb ris and finelea ves. Th e ree d is then retied , w ith tw o b ind ing s forea ch b un d le so tha t the stem s rem ain p arallel to e ac h

othe r w hilst the m aterial is b eing ha nd led b etw ee n stor-ag e an d the b uild ing site. M ost tha tch ers prefer bu nd lesof ap p roxim ately 20cm d iam eter. D ry, w ell ventilated stor-ag e is e sse ntial.

Fundamental informationH un dred s of sp ec ies o f g rass are u sed ex ten sively forroo fing througho ut the w orld . A ltho ugh the superficial ap -p ea ran ce of g rass tha tch ed roo fs d iffers ac co rd ing to theskill of the thatcher and local b uild ing trad itions, there areon ly tw o fun dam en tally d ifferent m ethod s of thatching w ithg rass. The first use s g rasses w hich h ave stiff, cylind ricalstem s. In the ha nds o f a skilled tha tch er the resulting roofm ay last up to 7 0 ye ars. The seco nd uses g rass leavesw hich are flat and p liab le; this soft-stem thatch rarelylasts m ore tha n 15 yea rs.

Thatch is suitab le for m ost clim atic cond itions a s it offersexcellent insulation against he at and cold . Its m ain d is-ad vantag e is tha t it is com bustib le an d fire sp rea ds eas-ily b etw een closely sp ac ed tha tch ed b uild ing s. Fo r thisrea son m ost urban b uild ing law s forbid tha tch in tow ns.H ow ever, a n um b er of sim p le fire-retard an t tec hn iq ue scan b e e m p loyed , so tha tch is often the m ost eco nom icroofing in rural areas.

N on ethe less, thatch is d eclining in p opularity alm ost eve-ryw here. This is b ecause trad itional styles o f thatching ,w hich w ere a pp rop riate in self-co ntaine d rural ec on om iesca nn ot no w co m p ete w ith p op ular ind us trial p rod uc ts,p articularly iron sheets.

Basic techniques for processing and

useMaterials

Th e ch oice of m aterial an d the refore the tha tch ing tec h-nique ad op ted p rim arily dep end s on w hich spec ies a relocally a va ilab le in su fficient quantity. Exo tic g rasses a rerarely ec on om ic a s tha tch is b ulky and exp en sive totransp ort, although the increasing p opularity of thatch inno rthern E urop e has created a thriving internationa l m ar-ket for ree d in rec en t d ec ad es.

Fo r a roo f of a m ed ium sized ho use (ap p roxim ately

150m2. floor area) the m ost d urab le typ e o f thatch usesup to 3 ton ne s o f g rass. This is the an nu al p rod uc t ofab ou t 1.5 h ec tares o f inten sively m an ag ed m arsh ree d (aroo f of w hich m ay las t 60 years in a tem perate clim ate),

Harvesting water reed off Danish marshes


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Savannah grasses and cereal straw.

M an y spec ies a re u sed . Th e op tim um charac teristics a re

the sam e as for m arsh ree d , b ut ce rea l straw rarelyg row s m uc h taller tha n one m eter.

W he at p rod uc es the m ost lon g lasting tha tch , b ut thecultiva tion reg im e h as to p rod uc e stron g stem s ra the rtha n h igh se ed yield . The b est straw com es from w interso w n w he at. Tim ing the h arvest is c ritical to e nsure d rystraw w ith m inim al loss o f saleab le seed . M od ern com -b ine ha rvesters ca nn ot be u sed as they b reak the straw ,b ut sp ecial m ach inery ha s b een d evelop ed to c ut, bun -d le a nd com b the straw w hilst sep arating and b ag g ingthe see d .

La b ou r intense h arvesting of sava nnah g rasse s an d strawm ay be feas ib le b ut the labour inp ut can be significa ntlyred uc ed by m ac hine ry. R ec ip roc ating b lad e rice ha rvest-ers tha t are w idely ava ilab le in d evelop ing countries canea sily b e ad ap ted for grass harvesting . A s w ith ree d , theg rass m ust be c ut w hen d ry, bund led w ith the cu t end salig ne d and doub le tied after com b ing so tha t the stem sstay p arallel. P roc essing is d us ty w ork so fac e m askssho uld be w orn to p reve nt lung com plaints.

Soft stem grasses

The sam e c ultiva tion a nd ha rve st p rinc ip les ap p ly forg rasses w ith flat-b laded flexib le leaves rather than cylin-d rica l stem s. Particular care is ne ed ed w hen clea ning thistyp e of g rass; it often contains a high p rop ortion of verysh ort g rass w hich w ill red uce the roof life unless it isrem oved.

Roof structureA lm ost any sh ape o f roof of su itab le p itch (at least 45)

can b e thatch ed . S im p le s tructures w ithou t p rojectingch im ne ys or chan ges of pitch w ill last best.

Th e struc ture sh ou ld b e c ap ab le o f sup p orting up to40 kg . per squ are m eter, w hich is the w eight of the he avi-est m aterial m arsh reed . Tim bering , w ith sa w n, sp lit orrou nd tim b er, is c om p leted w ith ho rizontal b atten s se -cured to rafters a t app roxim ately 30c m ce ntres. It is es-se ntial tha t a tilting b oard w hich is 3 5m m thicker thansub seq ue nt batten s is fixed along the eaves a nd gab les.This forces the first laye r of thatch into tension and leadsto the rest of the tha tch b eing m ore tig htly com p ac ted

tha n it w ou ld othe rw ise be.

Thatching workThatching req uires sk ill, and exp erience; a trad itiona lap p renticesh ip lasts five years in E ng land . A lternative ly,se ve ral m on ths of inten sive tu ition fo llow ed b y e xp ertsup ervision gen erally prod uc es a c om p eten t tha tch er. A sw ith all roo fing w ork, p atien ce an d m eticu lous a ttention tod etail is invariab ly repaid w ith m inim al m aintenan ce a ndop tim um d urab ility.

Th atch dec ays as the surfac e rots. Th e ke y ind ica tor ofstiff stem g rass thatch is a n evenly thick coat laid co n-sistently com p ac tly over the e ntire roof surface . The o b -jec tive is to h ave the m inim um len g th o f ea ch stem ex-p osed on the surfac e w ith the h orizontal fixing for each

Mechanised combing of thatching grass in Zimbabwe

Stiff-stem grass thatch. Fixing options: 1. Fixing thethatch with stitching; 2. Twisted wire ties; 3. Steel orwood rod or sway; 4. Hooked thatching nails.

1

2

3

4


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20 cm thick laye r sec ured as d ee p ly as p oss ib le w ithincoat of thatch. If the fixing is too close to the su rface thethatch w ill be so c om pact that it can not d ry out quickly,and it w ill b ecom e e xpose d on the surfac e w ithin a fewyears. If it is too dee p shorter stem s m ay no t be sec uredan d exce ssive w ater pen etration w ill lea d to m ore rap idd ecay. O n a 3 0c m thick coat of tha tch laid at 50 eachfixing sho uld be 1 5c m dee p , m ea sured at right an g les to

the surface. A rule-of-thum b m ea sure of co m pac tne ss isthe tha tch er shou ld b e a b le to m an ua lly com p ress thene w thatch to a bout 90% of its full thickness.

Th e rid ge of b oth soft and stiff stem g rass tha tch is p ar-ticularly vulnerab le. If it is m ade of g rass the fixings w illha ve to be exposed on the surfac e; it w ill g en erally have

to b e rep laced every 10 years. H ow ever, m an y othe r m a-terials c an b e used for ridg ing , such as iron sheets, clay

tiles o r ferro-cem ent. The p rincip le is to ensu re that thefixing s of the up p erm ost layer of tha tch are co vered an dp rotec ted so tha t w ater can no t pen etrate into the b od y ofthe thatch.

Cost and economyE co no m y is a trad e-off b etw ee n thick ne ss o f tha tch ,w hich affects d urab ility, and the cost of thatching w orkw hich w ill ha rd ly va ry w ha tever the thickness. O n a ver-ag e, op tim um d urab ility is ac hieved w ith a 30 cm thick

co at of tha tch laid on a 50 slop e.A skilled thatcher, w orking w ith one a ssistant should b eab le to com p lete the roo f of a m ed ium sized ho use in 10days. U sing 3 tonnes of m arsh reed and a ferro-cem entrid g e (w hich req uires no m ainten an ce ) the roo f shou ldlast 70 years in a tem perate clim ate or 35 years in thetrop ics. B y m ost peop les d efinition, this is a perm anentroof.

The op portun ity cost of tha tch dep en d s o n ho w long itlasts com pared to a sim ilarly p riced roof of an a lterna-tive m aterial. In no rthern Europ e the p rice of ree d thatchis com parab le, ove r its life, to a roof of natural slate, andab ou t 30% m ore e xp en sive tha n a co nc rete tile roo f. Th etim e take n to thatch w ith s traw is sim ilar to w orking w ithreed , so the cost d ifference w ill d epend on the relativem aterial p rices w eig hted by the low er durab ility o f straw .

Fire preventionTh atch is com b ustib le, p articu larly d uring d ry w eathe r.H ig h q uality thatching is the first line of d efence as acom pac tly tha tched roo f is m uc h less p rone to ca tch ingfire tha n a loo se an d rag g ed co at of g rass. P reventivem ea sures sh ou ld aim to red uc e the risk from the m ostlike ly sources o f fire. These are m ainly d ealt w ith in alater chap ter; in ad d ition seve ral m ethods are p articularlyreco m m end ed w ith thatch.

If a fire does start it is w ise to have facilities at hand todea l w ith it. A hosep ip e c onn ected to a tap w ith sufficientp ressure to rea ch the roof is one m ethod . In p articularlyd ry c lim ates it m ay b e w orth fitting a p erforated m etalp ip e along the rid ge; w heneve r there is a threat of fire

the roo f ca n b e d ren ch ed . A sim p le p rec au tion is to h avea lon g ha nd led rake stored ne ar the ho use; if fire d oe sstart it m ay b e possib le to p ull off som e of the thatch tocreate a fire b reak.

Mechanised combing of thatching grass in Zimbabwe

Cross section through stiff-stem grass roof

C em ent/w irem esh ridg e cap

Fixing s m ust be a ll the sam edep th w ithin the tha tch

Tilting Fillet force s the firstlaye r into ten sion


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Fires often start insid e the ho use. Th e roo f m ay be p ro-tec ted by having an inc om bustib le ce iling fixed to the un -

d erside of the rafters.C hem ical fire retardants p rovide only tem porary p rotectionas the y are w ater solub le. Trea tm en t m ay b e req uired forp ub lic b uild ings tha t are thatche d , but it w ou ld add atlea st 30 % to the tha tch ing co st and w ou ld ha ve to b ered on e e ve ry few ye ars, so it is rarely econ om ic forho use s. R ec en t rese arch sug g ests tha t som e retardan tsm ay da m ag e the roof b y encourag ing m ould g row th.

Further Information

G roo t C .; The Progress of Decay and Weathering in

Thatched Roofs in Vegetable Plants and Their Fibresin Building ; R ILE M /C IB , Paris, 19 86

H all N .L.; Thatching: A Handbook ; Interm ed iate Technol-og y P ub lica tion s, Lond on , 19 88 .

Sw allen J.R .; Grasses Their use in Building ; U .S . D ep t.of H ousing an d U rb an D evelop m en t, 1972 Leaflet no . 1,W ashington 1955.

W est R .; Thatch ; D avid & C ha rles, N ew ton A bb ott, U K ,1987.

Potentials

U ses a w ide rang e of ind igen ous ren ew ab le m aterialsw ith ze ro artificial energy cost.

M aterial p rod uc tion offers com m ercial farm ing op p or-tunity.

La bou r inten sive w ork w ith em p loym en t poten tial.

H igh qua lity tha tch is w ea the rp roof, d urab le an d at-trac tive .

Tha tch has excellen t insu lation va lue.

A t the end of roof life w aste m aterial is e asily recy-cled a s com po st.

Inn ate shortco m ing s c an b e am eliorated . A fire resist-an t ce iling iso lates the thatch from fire and the occ u-p ants from insect or roden t pes ts that m ay infest theroof.

Limits

Th atch is c om b ustib le, and ino rd ina tely exp en sive tom ake c om pletely fire p roo f w ith ch em ica ls. Insuranc em ay no t be availab le o r the p rem ium s m ay b e verycostly.

It m ay ha rbou r inse cts a nd rod en ts.

Th atch ing is hig hly skilled lab ou r intensive w ork, andm ay thu s be e xp en sive. S aving lab ou r co sts throu g hp oo r or hasty w orkm an ship is a false e co no m y, asw ith all roofing .

S p ecia lise d train ing is nee d ed to introd uce newthatching skills.

S uitab le m aterials for g ood quality stiff-stem w ork m ayb e ve ry d ifficult to ob tain unless there is a lready a nestab lished thatching industry.

Trad itional thatch is o ften h eld in low reg ard as itrarely m ee ts m od ern d ay hou sing nee d s. C han g ingp eo p les a ttitud es m ay b e ha rd er tha n introd uc ing ane w tec hn iq ue of tha tch ing .

Checklist of benefits and problems for grass thatch


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Palm thatch

Fundamental informationP alm leaves a re w idely use d becau se they are so p len ti-ful and b ecause the y a re innately su itab le for roofing .Th ey are sim p le to p roc ess an d ea sy to fix to a roo fstruc ture. H ow eve r, eve n the m ost durab le p alm tha tch -ing w ill rarely last m ore than 7 ye ars, w hilst trad itionaltec hn ique s often ne ed an nu al rep air. Th ey a re excellen tfor tem porary structures, but for housing , peop le tend toch an g e to corrug ated iron or othe r m aterials as so on asthey c an afford it.

The leaves a re use d for roofing either in their naturalform , as they a re cut from the tree, or alternative ly, thelea f b lad es a re m ad e u p into m ats. Th ere a re se veralw ays o f m aking the se m ats. In E ast A frica the m ats areca lled m akuti. In m an y Fa r East co un tries the y are kn ow nas atap .

Basic techniques for processing anduse

Materials

P alm lea ves m ust b e m ature an d d ry be fore the y areuse d for tha tch . Eac h spec ies h as its ow n g row th c yclew hich m ay va ry ac co rd ing to so il co nd ition s an d c lim ate,b ut w ith m ost, the lea ves take a yea r to m ature. Fo rtha tch ing purpo ses lea ves are c lassified by the w ay tha t

the lea f b lad es are attac he d to the stem . Th ere a re tw otyp es.

C oc on ut (co co s nu cifera) lea ves a re the m os t w id elyav ailab le thatching m aterial in the h um id trop ics. H un-d red s of m illion s of peo p le rely on the m . A n average treep rod uces u p to 40 lea ves every year. The lea f com prisesup to 2 00 lea f b lad es w hich g row , at an an g le, to the lea fstem .

Fea the r shap ed leave s ha ve leaf b lad es w hich hang , usu-ally at an a ng le, on b oth sid es of a s traight stem . Fan-sha p ed lea ves have b lad es tha t rad iate from a w oo d y,fib rou s co re. D ou m p alm , w hich is often used in d rierp arts of A frica ha s fan shap ed lea ves.

M any other pa lm s prod uce fan sha p ed leave s. N ip a,w hich g row s in m arshy lan d is p rim arily c ultiva ted for itslea ves w hich are m ostly u sed for tha tch . Th ey last b etterthan coc onut lea ves, b ut cant com p ete w ith sheet or tileroo fing for m od ern ho using .

ProcessingTh ere are tw o w ays of p rep aring fea the r typ e lea ves to

m ake thatch m ats.In the first m ethod the lea f b lad es a re strip p ed from thestem an d the n stitch ed to a thin w oo d batten . Th is b at-ten m ay b e m ad e from the p alm lea f rib , or p erha ps fromsp lit b am b oo . Th e p rinc ip le for m aking the m ost durab lem ats is to m ake sure tha t the lea f b lad es a re sq ueeze dtig htly a nd neatly tog ethe r as they a re stitched onto theb atten . Th e stan d ard m at of 60 0m m len g th sho uld b em ad e of ab ou t 20 0 lea f b lad es. In E ast A frica this tec h-niq ue is c alled m aku ti. In Fa r E ast countries a sim ilartec hniq ue know as atap is used .

The sec on d m etho d is to sp lit the stem in tw o so the lea fb lad es hang from one sid e. Th e tw o p ieces a re laid b ac kto b ac k an d the lea f b lad es w ove n tog ethe r to form am at. Th is tec hn iq ue , w hich is com m on ly p rac tised insouth Ind ia, is n ot as d urab le as the first as the rap idd isch arg e of rainw ater is im p ed ed b y the w eaving p at-tern. B ut it is quicker to m ake the w oven m ats an d , asthe y are lon g er tha n the othe r typ e, tha tch ing w ork canbe d on e faster.

Fan-shap ed leaves gen erally n eed no p rep aration othe rthan d rying and flattening . They are tied , nailed orw ed ged into p lac e o n a roo f w ith the lea f b lad es fac ingdow nw ards.

Nipa palm thatch in the Philippines


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Roof structuresA steep p itch of at least 45 is essential. The s tructure,w hich m ay m ost econ om ically be m ad e w ith tim b er orb am b oo p oles rather than saw n tim be r, nee d s to b estrong en ough to supp ort up to 20kg /m 2 of thatch. H ori-zontal battens a re n ot ne eded for feather-typ e m ats; therafters ne ed to b e se t ab ou t 500m m ap art for m ats tha tare 600m m long . A s w ith all roofing , it is advisab le to fixa b atten of ap p roxim ately 60 m m thickn ess a lon g thelen g th of the eave. This p rovides essential support for thefirst layer of tha tch . A bam boo pole of this d iam eter w ill

serve the sam e p urpo se.

For fan -typ e lea ves horizontal b atten s are n ee d ed , usu-ally at 15 0m m ce ntres.

Roofing workTh e p roc ess o f laying fea the r typ e m ats resem b les tiling .

M ats a re tied to the rafters in ove rlap p ing laye rs startingat the eave . The thickness o f the c oat, and therefore thed urab ility of the roof d epend s on the size of the o verlap .There should b e a m axim um of 100m m betw een them ats; if su fficient m aterial is a va ilab le this g ap sh ould bereduced to 60m m .

It is som etim es suggested tha t p alm tha tch req uires sid elap as w ell as ve rtical overlap , b ut this sh ould b e u nn ec-essary w ith w ell m ad e m ats. In fac t, this m ay b e a posi-tive d isad vantag e as the extra thickne ss created b y eachside-lap crea tes rid g es in the surface w hich w ill lead to

the form ation of gulleys and m ore rap id dec ay.

W ove n c oconut p alm m ats are g en erally laid dou b le thick,layer by layer, to a chieve acc ep tab le durab ility. W hen theupper layer d ecays, usua lly w ithin tw o years, the roof isretha tch ed . The d ec aye d up p er laye r is d isca rd ed an dthe low er layer the n form s the ne w up p er layer.

H ip and ga ble e dg es a nd the rid ge s of p alm thatche droo fs a re p articu larly vu lne rab le to w ind an d rain dam ag e.H ip e d ges ca n b est b e p rotected w ith a m etal ca p . G a-

Makuti type palm thatch mat the complete mat is600mm long x 500mm wide.

Woven coconut palm thatch mat

Inside view of fan-shaped palm thatch

Inside view of coconut palm thatch, in the Philippines


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b les shou ld eithe r be stren g the ne d w ith ad d ition al lash-ing , or p referab ly set w ithin parap et ga b les w ith a su it-ab le flash ing . The ridge cap is vital to ensu re that raind oesn t penetrate into the body of the thatch. The s im -p lest tec hn ique is a m etal shee t sadd le, but an y w ater-tig ht m aterial, such as ferro-cem ent shou ld be effective ,p rovid ed it is w ell secured .

Layering of woven palm thatch. Closer spacingproduces a longer lasting thatch

Peru palm thatch

in Indonesia this type of palm thatch is up to 200mmthick

Cost and economyTh e follow ing d ata a p p lies for m akuti typ e p alm tha tch -

ing . W ith w oven p alm m ats and fan sha pe d pa lm leavesquantities w ill be sim ilar, b ut d urab ility w ill also b e con-siderab ly less.

Materials

Fo r a fea the r-typ e p alm roo f w ith a slop e of 50 and ver-tica l lap betw ee n the m ats of 60 m m , 1m 2 of roof surfacew ould use 25 pieces o f 600m m -long m ats. A n a verag esized ho use w ou ld use ap p rox. 2,50 0 m ats, p lus stringor fib re for tying and su itab le m aterial for rid g ing .

Labour

P rep aration of m ats. This w ork is trad itiona lly d one b yw om en a s a cottage ind ustryso the p roduction rate isvery variab le, up to 40 m ats per d ay.

Roofing work

A skilled thatch er, w ith on e assistant w ould exp ect to layup to 5 00 m ats per d ay. S eve n w orking days, inc lud ingridg ing and tid ying the s ite is su fficient for an a ve ragesized hou se.

Durability

A stee p roo f w ith a thick tha tch is m ore d urab le tha n athin, shallow p itch ed roo f. Th e hig her co st of a steep er,thicke r roof is m ore than offse t b y the increased life, b utchoice is a lw ays a trad e-off betw ee n co st an d p erform -anc e. The m axim um eco nom ic life o f a p alm thatch, us-ing the b est ava ilab le m aterials and a skilled thatcher is10 years.

Further Information

Trelau n B .; Tuiles de Bois USA and Canada ; G R ET,Paris, 19 84 .

Pow ter A .; Papua New Guinea Shingle and ShakeManual ; Fo rest P rod uc ts R esea rch C en tre, PN G , 197 6


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PotentialsP alm lea ves are w idely availab le and usua lly ine xp en -sive , esp ecially in the h um id trop ics.

H arvesting , p roc ess ing an d tha tch ing w ork is lab ou rintensive .

S kills are w idely know n w he re p alm lea ves are a vail-ab le, and are e asily learnt.

R ep air an d m ainten an ce is straightforw ard .

P alm tha tch is light in w eight, so roof tim bering ne ed

no t be very exp en sive.

Th eir therm al insu lation va lue is h ig h, so p alm lea froo fs are com fortab le in w arm clim ates.

This typ e of roof looks attrac tive , it b lend s w ell w iththe na tural environ m en t an d , being a ren ew ab le m a-terial, is ecolog ically sound .

Lig htw eig ht roofing is less dang erous in e arthq uakezone s tha n m on olithic, hea vy roofing .

Tho ug h e asily d am ag ed in h igh w ind s, they are e asy

to repair or rep lace.

LimitsTh atch is c om b ustib le, and ino rd ina tely exp en sive tom ake c om pletely fire p roo f w ith ch em ica ls. Insuranc em ay no t be availab le o r the p rem ium s m ay b e verycostly.

C om b ustib ility a nd lim ited life sp an restricts u se tob uild ing ow ners w ho have read y ac ce ss to lab our andm aterials.

H arvesting and proce ssing has not be en m echa nised,so inexp ensive lab our is e sse ntial.

The ed g es hip s, ga b les a nd rid g es o f p almtha tch ed roo fs are ve ry vulne rab le to w ind dam ag e,un less p rotec ted b y a m etal she et ca pp ing .

Trad itiona l m etho d s are o ften very short lived so peo-p le m ay be reluc tan t to invest in m ore exp en sive p almthatch.

Trad itiona l palm tha tch is a ssociated w ith tem p orarystructures and p rev ious g en eration s, thu s not p er-ceived to be m odern.

C om b ustib ility m ea ns tha t urb an use is no t rec om -m end ed . A nd in reg ions p rone to civil conflict this isa m ajor draw bac k.

R elative ly low initial co st m ay b e a false ec on om ycom p ared to m ore d urab le and less com bustib le cov-ering s.


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Wood tiles(shingles and shakes)

Fundamental informationS hing les an d shakes are w oo d tiles w hich are eithe r sp litor saw n from b loc ks of un sea son ed tim b er and laid inoverlap p ing layers on a slop ing roof. M any d ifferent tim -b er sp ec ies a re su itab le a nd the y can b e m ad e e ithe rw ith s im p le h an d too ls or in sop histica ted m ec ha nisedfactories. The resulting roof can last 70 o r m ore years,d ep en d ing on sp ec ies, p rese rvative trea tm en t an d onexp osu re co nd ition s.

B am boo can also b e sp lit to m ake roo f tiles.

S p lit w oo d shake s have a very lon g history. In E uropeoa k sh ake s w ere use d for m ed ieva l b uild ing , in N orthA m erica reco rds sho w that ced ar shakes w ere used b ythe first old w orld se ttlers. In C an ada untreated w esternred ce d ar shake roo fs ha ve b een kn ow n to last ove r a10 0 ye ars. Tod ay w oo d tiles a re u sed throu g ho ut the

w orld . The econom y offered by m od ern tim ber p rocess-ing and p reserving m ethod s m ean s that saw n sh ing lesare now m ore w idely used than sp lit sha kes.

Basic techniques processing and useMaterials

Straig ht g raine d tim b er, p referab ly from a m ature hard-w oo d tree m akes the b est w oo d tiles. R ed ce d ar an doa k, trad ition ally u sed in E urop e an d A m erica , are verydurab le b ut m any othe r sp ec ies a re su itab le. C ho ice d e-pen ds p rim arily on w ha t is loc ally ava ilab le. Softer w ood sshou ld be trea ted w ith p reservatives.

For eco nom y and less w aste the tree sh ou ld be m inim um400 m m d iam eter and w ithou t b ran che s for first 5m . W ood

tiles shou ld be m ad e w he n the tim ber is freshly cut, b e-fore it d ries.

ProcessingTree trun ks a re saw n into log s a t lea st 45 0m m lon g .

Shakes a re sp lit using a froe a nd w ed ges. Th e p roc essof sp litting leave s a slig htly roug h surface w hich g ive ssh ake roofs a d istinctive and aesthetically attractive ap -pea ran ce . Th e w ork is lab ou r inten sive a p ositive ad -vantag e w herever unem ploym en t rates a re h ig h.

S hing les are c ut using a s aw . S aw ing cu ts a cross thenatural fib res of the tim b er, so w ater penetrates sh ing lesm ore rea d ily tha n sha kes.

Wood tiles are split to make shakes

Shingles are sawn wood tiles

Shakes are split fromblocks of timber

Shake makers tools thewedge shape of the froe is

important as it splits thewood whilst the handleprovides leverage

WedgeFroe

4 00 m m

7 0 0

m

m

7 0

m m

7 0m m

7m m


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B oth sha kes an d shing les a re w ed ge shap ed slig htlythicker at on e end .

M any saw m ills have e qu ipm ent that can p rod uce sm allsaw n b oa rd s from off-cu ts w hich m ay o the rw ise b ew asted . Th is m ay b e a low cost sou rce as sh ing les. Fo rexa m p le, in M yanm ar (B urm a) plyw ood off-cu ts sea ledw ith old en g ine oil a re the ch ea p es t roo fing m aterial.Th ey last ab ou t 6 ye ars. A ban d -saw or a ve ne er lathecan be used.

A p urpose m ad e c ircu lar blad e sh ing le sa w set w ithin a

flat-b ed stee l fram e is m ost p roductive . This is n ot w orththe inve stm en t un les s a sub stan tial m arket ca n b ese rve d . A n efficient operation w ill require a sm all factoryab le to m an ag e ha nd ling , p roc essing , p reservative trea t-m en t, storag e a nd tran sp ort of raw m aterials an d p rod -ucts.

If p reserva tive trea tm en t is desirab le this is d on e b y d ip -p ing or by p ressure o r vacu um im preg na tion (see pag e23 for details).

Dimensions of wood tilesM in im um : 150m m w ide 450m m long 10m m th ic kM axim um : 250m m w ide 600m m long 25m m th ick

Quantity required for roofingTh e n um b er of tiles n ee d ed va ries w ith sp ec ies , roo f

slop e an d the exp osu re (the am ou nt of ea ch of tile ex-p osed to the elem en ts on the roo f surfac e). O n a verag e33 shing les a re n ee d ed for ea ch sq ua re m eter of roo farea. Th ese w ill w eigh b etw een 30 and 40kg, dep end ingon sp ecies. A m ed ium size hou se (150 m 2 floor a rea)w ou ld use a b ou t 3,30 0 tiles.

Roof structuresS hing les a nd sha kes m ust b e laid on a roo f w ith a m ini-m um slop e of 30, p referab ly 4 5 for b etter d urab ility.

B elow 30 rainw ater w ill not d isc harge rap id ly so tiles w illb e liab le to rap id d ec ay.

Th e roo f m ust b e d esig ne d to su pport w eig ht of 30 40 kg /m2 R after spacing : 600 to 150 0m m , B atten size: 75m m 20 m m for 150 0m m rafter spa cing , less for closer rafters.

B atten spacing: 180m m 210m m centres, dep end ing onroo f slop e an d exp osu re of shing les.

A g eneral p rincip le is that the roo f d esig n, as for thatch,sho uld p referab ly b e sim p le w itho ut ch an g es of slop e.B ut w oo d tiles a re a flexib le c overing so w ill ac co m m o-d ate irreg ular shap ed and cu rved roo fs.

Fire risk m ea ns tha t un trea ted tiles shou ld no t b e usedon pub lic b uild ing s. A nd build ing law s m ay p roh ib it the iruse in u rb an area s.

A modern wood shingle roof in Germany

A wood tile roof showing key features of bestpractice


19/35


Roofing workTiles are laid in ascen d ing layers starting w ith a doub le

thick layer at eaves and verges. Each tile is se cu red tob atten s w ith tw o no n-rusting na ils (cop per, alum inium org alvanized stee l) ha lf w ay up ea ch tile. W ork is com -p leted laye r by laye r to the ridg e, overlapp ing to c overna iling and to create des ired exp osure of tile on the sur-face (see tab le). A vo id ve rtical joint ove rlap s and allow5m m ga p b etw een ea ch tile for expa nsion and m ovem ent.A t the ridge, hip s and va lleys, p rovide p rotec tive un der-lay of tar pa p er or thin she et m etal. Th e rid ge m ay b em ad e of tiles, or a m etal cap p ing w ide enoug h to cove rthe nailed fixing of the up p erm ost layer of tiles on each

sid e of the roof.

PerformanceD urab ility d ep en ds o n sp ecies, roof ang le, leng th of tileexp osed and clim ate. U p to 7 0 ye ars in tem perate zo neon 45 % roo f slop e, 30 yea rs in h um id trop ics.

CostVa ries w ith lab ou r rate and co st of m aterial. A tea m oftw o skilled tilers c an lay up to 20m 2 p er day. In E urop e,finish ed roof p rice per m 2. is com parab le w ith a clay tileroo f, but m ore exp en sive tha n c orrug ated iron .

MaintenanceA stee p ly p itch ed roo f sho uld req uire less m ainten an cethan a flatter one; rainw ater w ill run off quickly a s d ecaysho uld b e slow er. W he ne ver ne ce ssa ry, m oss, fallenlea ves a nd fun g i shou ld b e rem oved from the roo f b yb rushing , but avoid clim b ing on an old roo f.

A co pper strip or thin c ab le, fixed alon g the ridge shou ldim prove durab ility. C op p er sulphate so lution c rea ted b yrain reacting w ith the co pper ac ts as an effective fung i-cid e/herb icid e.

If a leak occurs this m ay happen if a tile sp lits o r isd am ag ed , a tar pap er tileshou ld b e inserted betw ee nshing les .

Bamboo tiles and planksW here b am b oo is plentiful and know led g e of b am b oob uild ing ex ists, tiles or lon g p lanks c an be used for ve rylow -cos t roof co vering .

Flat tiles are m ad e from 300 m m long leng ths of bam boo.The culm should h ave a m inim um diam eter of 130m m .The tiles are m ad e b y han d by scoring g roove s aroun dthe circum ferenc e o f a b am b oo cu lm w ith a sharp chiselan d then flattening the c ulm w ith a m allet. The inn er p artof the cu lm internode d iap hragm ac ts as a tile n ib w hichcan b e u sed to h ang the tile from batten s. B atten s m ayalso be m ad e from len g ths of sp lit b am b oo . A tile roo fm ad e w ith flatten ed section s o f b am b oo is laid in thesam e w ay as any o ther flat tile or sh ing le roof.

A n alternative w ay o f using b am boo for tiling is to sp litb am b oo cu lm s into tw o e q ua l ha lf-cy lind er section s.Th ese are then laid on sp lit-b am b oo b attens like inter-locking S p anish tiles to create a roo f 3 layers thick a ndw eig hing ab ou t 25kg/m 2.

B am boo p lanks a re m ad e b y splitting len g ths of b am b oointo tw o section s. The leng th m ay b e as long at the roofsrid g e to eave leng th. The half-roun d sections interlockan d overlap ea ch othe r, like Span ish tiles. B am b oo p lan kroo fing w ill b e lig hter and m ore d urab le tha n b am b oo

tiles.

Th e durab ility o f the se tiles an d p lan ks is low as bam -bo o rots qu ickly w hen w et, bu t m ay reach a m axim um of

Inside view of a split bamboo tile roof

Red cedar shingles


20/35


ten years in a d ry c lim ate on a stee p ly ang led roo f. P re-se rva tive trea tm en t by d ip p ing in ch em icals w ill inc rea se

the co st b ut ensu re a m inim um life e ven in a w arm hu-m id clim ate to at lea st 7 yea rs. B am boo roo fs, in co m -m on w ith othe r b iom ass roo fing m aterials, are very com -b ustib le.

Further Information:

P ow ter A .; Papua New Guinea Shingle and ShakeManual ; Fo rest P rod uc ts R ese arch C en tre, Port M oresb y,PN G , 1976.

Trelau n B .; Tuiles de Bois USA and Canada ; G R ET,P aris, 19 84 .

Janssen J.; Building with Bamboo ; IT P ub lications, Lon-d on, 199 5

Shake roof and timber-clad walls

Optimum exposure for different shingleand shakes sizes on different roofslopes

Shingles

Tile length 1:4 slope 1:3 slope

400m m 90m m 130m m

450m m 105m m 135m m

650m m 140m m 185m m

Shakes

Tile length 1:4 slope >1:3 slope

450m m 185m m 185m m

600m m 250m m 250m m


21/35



Limits

Shingles

m ust use straig ht g raine d ha rd w oo d sp ecies w hichsp lit easily.

p rod uc ed m an ua lly so o utp ut rates a re low er tha nsaw n shakes.

are d im en sion ally s tab le b ec au se the y a re sp litrad ially leaving natural g rain intact.

eac h sh ing le is slig htly d ifferent size and ap p earanc eroofing w ork m ay take lon g er bu t the finished roo fm ay b e m ore attrac tive than shake s.

sh ing les are thicke r tha n sh akes so roof struc turem ust b e stron g er.

Potentials

Shingles (sawn wood tiles)

C an u se any sp ecies, bo th softw ood and hardw ood ,but avoid knotty o r tw isted tim ber.

M ech anisa tion g ives p ossib ility for high output.

S tand ard ised p rod uc t m ay b e less p lea sing ae sthe ti-ca lly tha n sha kes.

M ust b e treated w ith p reserva tive s, p referab ly b yp ressure im preg na tion but this p reven ts w ater col-lection from the roof.

S hing les a re thinn ner tha n shakes , so roof struc turem ay be lighter.

Shakes (split wood tiles)

N ee d no t b e trea ted w ith p reservative s rainw aterca n b e collec ted .

N ee d s sim p le h an d too ls to sp lit an d trim to s ize variab le p rod uc tion rate d ep en ds on skill an d lab ou ravailab ility.

C an be p rod uc ed close to tim ber reso urce or build -ing site, avoid ing exp en sive tran sp ort.

P rod uc es less w aste than sh ing les.

H ard w oo d sha kes a re n aturally m ore d urab le tha nshing les .

Shakes

nee ds expen sive m echan ica l saw s (b and sa w or cir-cular saw ) and rig orous m ana g em ent of p roce ssingp lant.

m ore w aste than shing les.

ce ntral p roc essing m ay m ea n exp ensive tran sport tob uild ing site.

d im en sion ally unstab le -tend to w arp , crack and cu pw hen w et d ue to exp osure o f saw n tim b er fib res shakes are o ften less d urab le.

stan dard ised p rod uc t allow s m ore rap id roo fing w ork.


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Roof sheets withorganic fibres

Fundamental informationFib re reinforced roo f sh eets m ad e p rim arily of org anicm aterials, or reinforce d w ith g rass stem s, fib res or w oo dchip s offer consid erab le p otential for low -cost roofing .They a re light in w eig ht, can utilise w aste m aterials and ,in p rincip le, should be an attractive alternative to thatch,co rrug ated iron or asbestos cem en t she ets. R ese arch inm an y co un tries h as sho w n tha t a w ide va riety of fib rou sorgan ic m aterials are suitab le.

H ow eve r, this p rod uc t ha s ha d very lim ited com m ercialsuc ce ss in the d om estic roo fing m arket in d eve lop ingcou ntries . The y a re m ore ev id ent in use for ind us trialb uild ing s and em ergen cy, post-d isaster housing . The bestq ua lity sh eets can last for up to 1 5 years, b ut standardq uality sheets in a trop ical clim ate are rarely functional form ore than 6 yea rs.

Basic techniques for processing anduseTh ere are tw o typ es of she et.

The first is a corrug ated sheet m ade o f fine fib res w hichare b on ded tog ethe r an d w aterp roo fed w ith a spha lt.

Th e sec on d typ e a re flat shee ts w hich use large r fib res,such as w ood chips. They are b ond ed w ith cem ent andthe n c oa ted w ith a sealer.

Corrugated asphalt roofing sheets(ARS)S uitab le fib res are ob taine d from a w ide ran ge of m ateri-als includ ing b ag asse , sisa l, co ir, cocon ut, cotton andw aste p ap er. The y are p ulpe d a nd w ashed to rem ovesug ars an d starches. The w et m ixture is the n sp un in acentrifug e . The resulting m at is d ried , trim m ed to thed esired size an d the n p resse d b etw ee n co rrug ated d iesb efore b eing p ressu re im preg na ted or d ip coated w ith h ot

p aving -g rad e a sp ha lt. Fina lly the sheet ca n b e p aintedw ith asp halt, a lum inium or acrylic se a ler for furtherw ea the r p rotec tion . A sp ha lt is ap p roxim ately 50% of thep rod uc t w eight.

DimensionsShee ts are 6m m to 8m m thick, betw een 500m m and900m m w ide and betw een 900 and 1830m m long. M ostm anufacturers sell a va riety o f size s to su it d ifferent ap -p lications.

WeightD ep en d ing on the thickne ss, betw een 3 a nd 5kg /m 2.

Uses of ARS sheetsA R S she ets a re sim ilar to co rrug ated iron an d asb estoscem en t sheets and are suitab le for all typ es of build ing .

They a re particu larly u seful for tem porary structures suchas em ergen cy housing.

Roof structureM inim um roo f ang le is 22 . S heets ne ed sup p orting onho rizontal b atten s fixed to rafters at m axim um sp ac ing of500m m .

Fixing methodS he ets are n ailed top and bottom , starting at the b ottomof the roo f an d ove rlap p ing both sid e an d top . Sp ec ialsha ped rid g e p ieces a re used to p rotec t the ap ex.

The final coat on asphalt roof sheets (Colombia)


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CostVaries w ith thickness a nd size . In Ind ia (1994) sh eets

co st ap p roxim ately on e-third the p rice of asbestos-ce m en tshee ts and ha lf tha t of corrugated iron sheets, but low erd urab ility m eans tha t A R S m ay b e a poo r investm en t.

DurabilityVa ries w ith q ua lity up to a m axim um of 15 yea rs.

Th e q ua ntity of aspha lt an d the uniform ity of im preg na -tion is v ita l to avo id d eform ation or d e-lam ination ofshee ts. R esea rch show s c on siderab le variation in qua lity

an d the refore durab ility b etw ee n m an ufac turers in devel-op ing co un tries suggesting a ne ed for better qu ality con -trol.

Fire p roo fing ch em ica ls c an b e inc orpo rated d uringm an ufac ture, at ad d ition al co st. Th e she ets rea ch classB m od erate (U S stan d ard ) fire rating w itho ut ad d i-tional treatm ent.

Production and economics

A R S shee ts are m anufactured in m any coun tries a roun dthe w orld . P rod uc tion eq uipm en t varies in ou tput. Typ ica llab ou r inten sive p roc ess ing , us ing Ind ian eq uip m en t(sou rce M A S , K erala) w ith 10 0 em p loye es p rod uc es am axim um of 1 m illion shee ts (2m 1m ) pe r annu m . M a-ch ine ry (inc . sp ares an d lab oratory) co sts ap p roxim atelyU S $ 1 .1 m illion (1993 ) and w ou ld be sited in a 15 00m 2

b uild ing w ithin a 15 ,00 0m 2 factory site w ith 400 to 500w orkers.

A n A R S fac tory sho uld be sited ne ar a river, close to rawm aterials sources a nd aw ay from residen tial areas d ue to

p etroleu m /aspha lt od ou rs. If shee ts a re to be sun-dried alarg e yard and 200 sunny d ays p er year are necessary.

StandardsM any coun tries have standard sp ecification s for this typ eof she et, but there is no interna tionally a ccep ted stand -ard. Ind ian S tan dard N o. 12583.1988 is typ ical; it d etails:as p ha lt con tent, w ater ab so rp tion , w eig ht b earingstren g th, beh aviou r at high tem perature, an d d im en sion alstab ility in va rying cond itions.

Particle boardS he ets a re form ed from w oo d ch ip s, othe r sm all size

ligno-cellulose chip s o r fib rous m aterials. A ve ry extensiveran g e o f crop resid ue s, w oo d ch ip s an d ag ricu lturalw aste m aterials w ere tested for su itab ility w ith d ifferentb ind ers d uring the 19 70 s in m an y c ou ntries. Th e m aterialis tho rou g hly w ashe d an d the n b len d ed w ith a b ind erbefore b eing eithe r ho t p ressed or extrus ion p ressed toform she ets. Th ese m ay be c orrug ated or flat. The sheetsshou ld be co ated w ith a w ea the r-p roo f p aint for externaluse this is usually d one in the fac tory. The p rice an ddurab ility w ill d ep en d on the typ e of b ind er use d .

C om m on b ind ers are cem ent, m ag nesium oxychlorid e or

pheno l-form ald ehyde resin. C em en t b onded sheets con-tain 62 % ce m en t, 28 % org an ic fib re w ith op tion al ad d i-tives su ch as sod ium silica te to im p rove d im en sion al sta-b ility. A w ater-p roo f coating has to be app lied if sheetsare used for roo f clad d ing .

DimensionsThickne ss 4m m to 40 m m , for roof clad ding . 15m m isrecom m end ed . C em ent bo nd ed sheets are prod uced inIndia in tw o sizes 2240 1220m m or 3050 1220m m .Exac t sizes w ill d ep en d o n the m an ufac turing eq uipm en tbeing use d , an d she ets ca n b e cut to the desired sizew ith a h an d -saw . M ost b oa rd s a re flat, b ut co rrug atedpanels can be m ade.

WeightVa ries w ith thick ne ss u p to 15 kg /m 2 fo r roofing g rad eshe ets.

Roof structureSim ilar req uirem en ts as for asp ha lt shee ts. M inim um roo fan g le is 22, stee p er ang le w ill be m ore d urab le. S he etsne ed sup porting on ho rizontal batten s w hich are n ailed torafters at m axim um spac ing of 500m m .

Resistance to termites and fungiTh e fib res are m ineralised w ithin the b ind er an d are thusnot su sc ep tib le to inse ct or fung i attack.


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UsesS uitab le for all typ es of build ing , but roof m ust be acc es-

sib le for period ic re-sea ling an d m ainten an ce .

Uses

S he ets are na iled or preferab ly screw ed to the batten s.If flat (rather than corrug ated ) sheets a re used the ve rti-cal joints b etw een sheets m ust b e filled w ith a flexib lesealing com po und , and screw head s m ust also b e sim i-larly p rotected .

DurabilityD ep en ds on the roo f slop e, the qua lity of the w aterproo fco ating an d on clim atic exp osu re. 10 yea rs is m axim umexp ected life for a reg ularly m aintained roo f on a 35slop e in trop ical cond itions.

CostC om m ercial p rod uc ts in Ind ia, p er m 2 of roofing , costap p roxim ately the sam e as a sp ha lt co rrug ated she ets.P rices vary according to the c os t of the b inder, p rice o fthe organic m aterial an d the scale of tec hn olog y.

Production and economicsE q uip m en t is ava ilab le from a num b er of m an ufac turersto su it w idely va rying p rod uc tion co nd itions. The largestsca le m ec ha nised fac tories o p erating on a c on tinu ou sb asis w ith a m inim um of m anu al han dling m ay p rod uceup to 8 00 ,00 0 roo f she ets (2m 1m ) p er yea r. Th e

eq uipm en t co st w ou ld be a t lea st U S$2 m illion (19 92 ), ex-clud ing land , build ing and staff costs. Th e sm allest-scalep lan t, suc h a s tha t d eve lop ed by the N atural R eso urce sInstitute (N R I) in the U K , ha s a n ou tput of abou t 25 0,00 0shee ts per year ou tp ut.

Further information:

B ryan t B .S .; Corrugated Roofing Panels from Agricul-tural Residues ; A p p rop riate Te ch no log y. Vo l. 4 N o. 4,1978, Lond on.

Composite Roofing and Panelling Materials from Woodwaste and Agricultural Fibrous Residues for Low-costHousing ; C onstruction Ind ustry A uthority o f the P hilip -p ine s, M an ila, 19 86 .

Flynn G .; An Industrial Profile of Fibreboard PanelProcessing ; Trop ical P rod ucts Institute, Lond on , 198 0.

Ind ian B ureau of S tan dards, D elhi.

Lig htR oofing s Ltd . H ard iyan S ing R oa d , K arol B ag h, N ewD elhi 11 0 0056 .

N C L Ind ustries, B 87 D efenc e C olony, N ew D elhi110024.

M ech anical A ssem b ly S ystem s, M ayithara M arket, PO

A llep p y D istrict, K erala 68 8539, Ind ia. (for A R S eq uip -m ent)

N atural R esou rce s Institute, C en tral A ve., C ha tha m , M E44TB , U K (for p article b oard inform ation.)

Asphalt impregnated sheets tend to warp andde-laminate in tropical conditions


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Checklist of benefits and problems for roof sheets with organic fibres

PotentialsLig ht w eig ht e asy to tran sp ort an d req uires lig htroof structure.

H igh streng th/stiffness to w eight ratio.

Suits all typ e of build ing s, esp ecially low -cost hous-ing an d tem porary bu ild ing s.

C an b e m ad e fire-p roof so m ay b e use d in urban a r-eas.

U tilise s o rg anic m ateria ls that m ay o the rw ise b e

w asted eg w ood ch ip s, bag asse, co ir.

R oo fs ca n b e u sed to c ollec t w ater if w ea the rp roo fcoating is non-toxic.

Fairly low skill needed to fix the sheets.

Low m aintenance.

C an be m ad e in eithe r sm all or very large fac tories.

Low cost co m p ared to o the r m etal or asb estos c e-m ent shee ts.

A spha lt im p reg na ted she ets a re na turally m ore w ea th-erp roof and d im ensionally stab le than flat p artic leboard.

LimitsLow durab ility.

M ust b e m anufactured in centralised factories req uir-ing high level of m an agem en t skill an d q uality control.

B ind er, fire-retard ants a nd w ater-p roo f coa ting s m ayhave to b e im po rted and m ay be e xpe nsive.

Low custom er/house-ow ner ap pe al be cause of po ord urab ility, va riab le q uality and usu ally unattractive col-our.


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Treatment ofbiomass materials:preservation

Fundamental informationA ll org anic m aterials de com pose w hen exp osed to m ois-ture a nd he at. M axim um durab ility is ac hieved by se lec t-

ing the b est m aterials, harve sting at the right tim e andb y processing an d using the m acco rd ing to b est p rac -tice p rincip les d esc ribed in p revious chap ters. S ervice lifeca n a lso be im prove d by p rese rvative trea tm en t.

S om e sp ecies are m ore d urab le than others, and som ep arts of p articu lar spe cies, for exam p le the sapw oo d oftim b er used for shing les, sho uld be d isca rd ed . R esearchinto conventional p ractice suggests that it is very unlike ly,w ith the sing le exce p tion of co pp er sulpha te he rb icides,tha t ch em ica l p rese rva tion of g ras s o r p a lm tha tch iseco nom ic treatm ents a re either ineffec tive or excessive ly

co stly. In c on tras t, ch em ica l trea tm en t of w oo d or ba m -b oo tiles is generally viab le.

Non-chemical preservationB efore dec id ing to use ch em ica ls it is advisab le to co n-sid er othe r m etho d s tha t m ay b e eq ua lly e ffec tive,ch ea per an d less d an gerou s. W hereve r organ ic m aterialshave b een trad itionally u se d for roofing it is very like lytha t p eo p le w ill ha ve d evised no n-chem ica l p reservativetec hn iq ue s.

Fo r exa m p le, in the Philipp ine s it is com m on kno w led gethat b am boo w hich is to be used for roof tiles w ill b etterresist w ood borer infes tation an d g en eral decay if it hasb een soake d for a d ay in se a w ater. The y also know thatb am boo w ill be less like ly to sp lit if it has b een harvestedw hen the cu lm s a re fully m ature . S im ilarly, farm ers inE ng land know tha t it is e sse ntia l to a llow new ly cutthatching straw to d ry thoroughly b efore it is stored read yfor sale. Lo ca l ad vice is alw ays rec om m en ded .

Chemical preservationP reserva tives im p rove durab ility b y m inim ising or p reven t-ing m icrob ial or fun gal action, attack b y insects and b y

m aking a m aterial less p rone to w ater p ene tration. Th em ost effec tive trea tm en ts c an be exp ec ted to d oub le the

natural life of a m aterial. H ow ever, m an y che m ica ls a rew ater solub le o r are lea ch ed ou t b y m oisture c ha ng esan d thu s b ec om e ine ffec tive w ithin a few years.

Safety precautionsW orking w ith c he m ica lly trea ted m aterials poses a ha zardto the roofing contractor. S p ecial p recautions m ust b etake n to e nsu re tha t ha nd s are w ash ed b efore e ating ,an d ca re m ust be take n to avo id inh aling toxic d us t ifm ec hanica l saw s a re use d to trim trea ted shing les.

Th ere a re hu nd red s o f d ifferent com m ercially a va ilab lech em ica ls an d m ixtures o f ch em ica ls. A s the y are so ldun der a variety o f trad e na m es it is im p ortan t to ch ec kthe p recise c om p os ition o f a p articu lar p rod uct b eforesp ecifying its u se . C hem ical use is c ontrolled by leg isla-tion tha t d iffers from co untry to coun try, so advice m ust

Danger symbols must commonly encountered inconstruction

E xplosive H ig hly flam m ab le

Toxic C orrosive

H arm ful or Irritant O xid ising


27/35


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so aked for seve ral days to a chieve effective p enetration.It m ust be d ried before it ca n b e used . It is not ec on om icto soak thatch due to the quan tity of m aterial involved .

Th e ad vantag e of op en tan k so aking is its sim p licity andinex p en sive e q uip m en t. S m all b atche s of m ateria l, forexa m ple for one roo f, ca n b e trea ted econ om ica lly. H ow -ever, this is offse t by the d angers associated w ith o p entan ks o f chem ica ls.

M an y d ifferen t tec hn ique s have been devised to inc rea sethe p en etration rate and m ake the p roc ess safer. Im preg -nation in sealed vesse ls e ithe r un der ne g ative p ressure(vacu um ) or positive p ressure is m ore effec tive tha n soak-ing . S im ilarly, inc rea sed pen etration m ay be ac hieved b yhea ting the c he m ica ls. A ll of the se p roce sse s req uiresp ec ialised eq uipm en t an d ca reful m anag em en t; if the sefacilities exist locally roofing contractors should use themin p referen ce to o the r p reservative m etho ds.

S ap d isp lacem en t, w he re p rese rvatives are d raw n into them aterial by cap illary action.

D isp lacem en t m etho d s are o nly useful for trea ting b am -b oo tim ber for shing les a nd shakes is best trea ted byp ene tration m ethod s. Tw o tech niques ca n be used ; bothm ust be d one w ith freshly cut bam boo.

B utt trea tm en t is w he re b am b oo cu lm s are stoo d in ad rum of p rese rvative. The leaves a ct as a pum p; as sa pevap orates it is rep lac ed by the ch em ica ls. Th e p roc essm ay take several w eeks.

The B ouc he rie M ethod uses g ravity pressure or a p um pto force p reservative in to the b am b oo . It ca n on ly b euse d w ith fresh ly c ut b am b oo so trea tm en t sho uld b estarted on the day tha t the bam b oo s are harvested .

ConclusionC he m ica l trea tm en t is g en erally eco no m ic for w oo d tiles.Th e safest an d m ost effec tive m etho d s req uire exp en siveind ustrial eq uip m en t. B am boo ca n b e trea ted , b ut the reis no clea r ev id en ce tha t ex isting p roc es se s are e co -nom ic. D esp ite m any exp erim en ts and extensive resea rchthe re is no conc lusive evid en ce tha t tha tch can b e ec o-nom ically trea ted w ith p rese rva tive s. B est p ractices incultiva tion, m aterials se lection, harve sting and p rocessingand finally in a p p lication a re o f p rim ary im p ortance b e-fore ch em ica l trea tm en t is even co nsid ered .

Further information:

B erry R .W .; Timber in Tropical Building ; O verseas B uild -ing N ote 1 99 , B uild ing R ese arch E stab lishm en t, Eng lan d ,1993.

A Guide to the Safe Use of Chemicals in Construction ;C on struc tion Ind ustry R esearch an d Inform ation A ssoc ia-tion . Lo nd on , 19 81 .

Janssen J.; Building with Bamboo ; Interm ed iate Technol-og y P ub lica tion s, Lond on , 19 95 .

Pressure impregnation of bamboo using borax in Costa Rica


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Fire protection

Fire is a seriou s d isadvantag e w ith all roofs covered w ithorga nic m aterials. A p art from sand w ich ing the roo f co v-ering b etw ee n tw o incom bustib le laye rs the re is no w ayof m aking the m co m p letely fire p roo f. Th us tha tch an dshing les are rarely p erm itted for closely sp ac ed urba nb uild ing s and org an ic b ased sheet m aterials m ust con-

form to flam e p enetration an d flam e sp read stan dards.

H ow ever, various techniques have b een p roven to b e ef-fective ag ainst the m ost like ly sources o f roof fires.

Building designE lectrical w iring should carried out by trained contractors.It m ust alw ays b e p rop erly insulated an d ea rthe d . Particu -lar care m ust be taken if ca b les pass throug h roo f void san d attics w hich are rarely visited as rod en ts and insectsm ay d am ag e insu lation , so m etal or reinforced p las ticcon d uit shou ld be u sed .

C him ne y d esig n m ust isolate ho t flue d isch arg es an dm ust relea se the m at lea st one m etre above the hig hestp oint of the roof. C him neys should p referab ly b e b uilt ofm ason ry and roo f tim b ers sho uld no t b e b uilt into thechim ney.

C ooking arrang em en ts m ust m inim ise the chance of ac-cid ental fire.

B uild ing s sh ou ld be p rotec ted w ith lightning co nd uc tors.

A n o utside tap perm an en tly fitted w ith a lon g ho se-p ip eis a d visab le.

The se are co m m on-sense p reca utions w hich a lso have tob e co m plem en ted b y fire-co nsc iou s h ouseh old ac tivity.

It is a lso im p ortant to realise that skilled w orkm ansh ip islike ly to p roduce a roof cove ring that is less fire p rone.This is p articularly evid ent in the case of thatch; p oorw orkm ansh ip is like ly to p rod uce a loose ly laid thatchw hich is m ore c om b ustib le than a d ensely com pac t layerof thatch.

In ad d ition, there a re several tech nique s o f m inim ising thecom b ustib ility o f the roof m aterial and for red ucing thelike lihood that a fire w ill take hold in an organic roof.

Surface coatingVarious m ethod s ha ve b ee n d evised to cove r thatche d

roofs w ith a n incom b ustib le c oating . In Ind ia this w asdon e w ith a ce m en t/sand slurry, or a b itum en -stab ilisedearth p laster. B ut these ad d to the c ost of the roo f, in-crease its w eight and co m p letely h id e the orig ina l roo f.Their m ajor d raw back is that they crack, thus letting inw ater w hich ca uses m ore rap id dec ay o f the tha tch .

Chemical treatmentM ost fire retard ant chem ica ls a re w ater solub le; inso lub leon es a re m uc h m ore e xp en sive. B oth typ es a re rarely

use d b ec au se the y are u ne co no m ic. S trictly sp ea king ,m ost ch em ica ls act as flam e retard an ts (red uc ing the in-tensity o f fire) rather than fire p roofing agents.

D ip p ing is the b est w ay o f trea ting roof m aterials, b e theytha tch or shing les. B ut the se are w ashe d off the surfac ew ithin a year and hum id ity ch anges c an leac h the che m i-cals out of the m aterial.

B orax a nd boric acid , d iluted in w ater, are the lea st ex-pensive, safest and m ost w id ely use d ch em ica ls. W he na fire starts on a m aterial treated w ith these substan ces

the y fuse to form a vitreo us layer ove r the co m b ustib lesurfac e a nd so c ut off the sup p ly of oxyg en for co m bus-

Fire-protection for external fire-hazards

Perforatedridg e p ip e

Lig htningcond uctor

Perm anentw ater sup ply


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tion . H ow ever the solub le salts a re lea ch ed ou t of the d rym aterial w ithin the roo f co ating b y cha ng es in am b ien t

hum id ity.Trea tm en t co st dep end s on a num ber of factors, but canb e e xpec ted to ad d up to 50% to the co st of the roo fco vering .

Incombustible underlayFire ne ed s a co ntinu ing oxyg en sup p ly. Partial red uc tionof com bustib ility is achieve d by fixing a fire p roof lining(eithe r m etal foil shee t or gyp sum /ce m en t boa rds) un derthe roof, nailed to the rafters. Th e effect is to iso late theroof from the interior of the b uild ing . It is im p ortant toensu re that the thatch or tile cove ring is s till ve ntilated sotha t a dam p roo f ca n d ry rap id ly. Th is typ e of un derlayis ob lig a tory for tha tch in seve ral E urop ean c ountriesw here fire risk is p red om inantly from inside a build ing .

Sparge pipesP erforated m etal p ip es fixed to the top of eac h side of aroo f and co nnec ted to a w ater supp ly con trolled by a tapat g round leve l extinguish roof fires very effective ly a ndca n b e u sed to d am p a roo f w hen the re is a threa t offire. They are o b lig atory in parts of Southern A frica. B utthe y req uire w ater pressure ca pab le of de livering over 2litres of w ater per m 2 of roo f area per m inu te m ore tha nthe ave rag e d om estic su pp ly rate so sp ec ial arran ge-m ents have to be m ade.

ConclusionFire retardant treatm ent is d esirab le for org anic roo f cov-

erings. A s chem ical treatm ents are like ly to b e very ex-p en sive, the b est ap p roa ch is fire co nsc iou s d es ig n ofthe se build ing s c om bined w ith co m m on sense , esp ec iallyw hen there is a n increased risk o f a fire.

In c om m unities w hich have m any hou ses roofed w ithcom b ustib le m aterials it is p rudent to have a local fire-fig hting service an d em erg en cy p lan s sh ou ld fire b rea kout.

Further Information:

E lkins G .H .J.; The reduction of the Fire Hazard ofThatched Roofs ; Fire resea rch N ote no . 52 5, Fire R e-search S tn. B oreha m w ood , U K , 196 1

The Prevention of Fires in Thatched Roofs; C S IR N ote

no. X /B O U 2-5, N ationa l B uild ing R esearch Ins titute, Sou thA frica, 1971 .

Fire resistance Applications of Boric Acid and itsSalts ; 1945 . From B orax H old ing s Ltd , B orax H se, C ar-lisle S t, Lond on S W 1.


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Sources of furtherinformation

Inform ation a bout b iom ass roofing m aterials is ava ilab lefrom m an y d ifferent sources. Trad itional build ing m etho ds,suc h a s tha tch an d w oo d roo f tiles a re w ell doc um en tedin a rchitectural and anthropolog ical literature though cov-erag e ten ds to con ce ntrate on aesthe tic o r ethn og rap hicasp ects rather than the p racticalities o f roofing . It is not

so e asy to find p ub lished inform ation ab ou t the cu rren tavailab ility of org anic m aterials for build ing ; the literaturefoc uses m ore on ag ricu lture and ag ro-forestry.

In the p as t thirty years the re h as been c on siderab le re-search into w ays of im proving the perform an ce of trad i-tion al build ing tech niques. Som e of this research has re-sulted in sig nifica nt im p rovem en ts w hich ha ve su b se-q ue ntly b ee n ad op ted by the loc al co nstruc tion ind ustry.Th ey are m en tion ed in the releva nt ch ap ters. H ow eve r,ne w com ers to this top ic sho uld res ist attem p ting to rep li-ca te p rop osa ls m ad e in rese arch pap ers un less the y are

ce rtain that the se tech niques have stood the tes t of tim e.In p articular, b e w ary of fire-p roofing and p rese rva tivetec hn ique s for tha tch ; the ev iden ce sugg ests tha t the seare rarely e con om ic and in som e ca ses m ay be positivelyha rm ful. If in doub t, alw ays se ek advice from loc al ex-p erts in the b uild ing industry, un iversities, N G O s o r gov-ernm ent research ins titutes.

Where to look for informationH aving d ec id ed tha t a p articu lar tec hn iq ue or m aterial

justifies further inve stig ation, start w ith the d ocum entsm entioned in the F urther Inform ation section o f the rel-eva nt chap ter. If local lib raries a re unab le to ob tain these ,the B A SIN R oo fing A dvisory S ervice w ill he lp . Inform ationab ou t B A SIN is g iven at the end of this b oo k.

Th e rich est p rim ary source o f inform ation is alm ost alw aysloca l b uilders, build ing m aterials m erchants and ag ro-for-estry sp ec ialists. Th ey w ill know w hich m aterials and tech -niq ue s a re trad ition ally u sed an d shou ld be ab le to g ivecom m on-sense ad vice ab ou t any p rop osals for introd uc -ing ne w m etho ds to existing m arkets.

M any national and international rese arch institutes haveloc ally releva nt rese arch an d d issem ina tion p rog ram m es

ab ou t build ing . M ost p rod uc e reg ularly up d ated b ib liog -rap hies w hich co ver organic m aterials and the ir co nstruc -tion use s. M an y run an enquiry service an d m ost have aran g e of pub lica tions . O f particular note are:

C en tral B uild ing R esea rch Inst. R oo rkee, 24 7 672 , U P,Ind ia

N ation al B uild ing R ese arch Inst. P O B ox 3 95 , 00 1,P retoria, South A frica.

Lu nd C en tre for H ab itat S tud ies, Lu nd U niversity P OB ox 118, S -221 0 0, Lun d, Sw ed en

B A S IN ad visory service . S K AT ha s sp ec ial exp ertiseon roofing .

Literature about Roofing

Bibliographies

Links Between Population, Settlements and the En-vironment: A Literature Review ; Jill W ells, et al.Sc hoo l of C onstruction E con om ics and M ana g em ent,S ou th B ank U niversity, Lo nd on , 19 94

A n excellent an d up -to-d ate rev iew of literature on or-g an ic b uild ing m aterials w hich hig hlights e viden ce ofd eclining ava ilab ility in recent ye ars. It d raw s o n theexp erien ce of w ork in m an y co un tries a im ed at p re-se rving existing su p p lies and /or in trod ucing exo ticsp ec ies for construc tion use. It inc lud es a co m preh en -sive reference list.

Roofs in the Warm Humid Tropics of South EastAsia ; G . Land aeta and S . Larsson. Lund C om m itteeon H ab itat and D evelop m en t S tud ies, Sw ed en, 198 7.

Th is rep ort co ncen trates on SE A sia, but m uch of theinform ation is releva nt to other trop ical reg ions. It in-clud es a tho roug h b ib liog rap hy on key sou rce s (up to19 87 ) ab ou t roo fing arou nd the w orld .

Bibliography on Local Building Materials, Plant andEquipment ; U nited N ation s C en tre for H um an S ettle-m en ts, N airob i, K en ya.


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General Publications

P rac tical inform ation ab ou t ea ch roofing tec hn iq ue is

m en tion ed in ea ch ch ap ter. In ad d ition , the re are threep ub lication s w hich o ffer a thorough o verview of build ingand roofing w ith locally m an ufac tured or locally sourcedm aterials.

Appropriate Building Materials ; R . S tulz and K .M ukerji. S K AT Pub lica tion s (Sw itzerlan d ) an d IT Pub li-ca tion s (U K ), 19 93

Building Materials in Developing Countries ; R .J.S.Sp ence and D .J. C ook. John W iley & Sons, C hiches-ter. U K , 1983

Global Review of Traditional Roof Construction andGeneral Discussion of Roof Types and DesignGuidelines ; Pap ers by K . M ukerji to the U N ID O C on-ference on A lte rna tive R oo fing M ateria ls an d Th eirC on struc tion Techn olog ies. B eijing , 19 88 .


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Key questions

If you a re interested in roo fing w ith o rganic m aterials yo ushou ld be a w are of the im p lica tion s. C on sider:

ac ce p tab ility o f d esign an d ae sthe tic aspec ts

roofing m aterials

roo fing skills

costs, m anag em ent and investm ent

Ten key questions1. Is the re a dem an d for an a lternative roo fing solution

or for an im provem en t in trad itional tech niques?

2. D o you think pe op le w ould a ccep t bu ilding s w ith anb iom ass m aterial roo f?

3. A re suitab le m aterials a vailab le loc ally o r ca n the ybe p roduced ?

4. W ill the fire h azard c ha rac teristic of b iom ass roo fingb e a serious p rob lem ?

5. A re you aw are tha t all typ es of roo fing ne ed period icm aintena nce ?

6. D o you realise that a n ew roof covering m ay req uireother cha nges to the b uild ing structure?

7. Is you r reg ion p ron e to sp ec ific p rob lem s related to

b iom ass roo fing , such as b ush fires?

8. A re you p repa red to m ake an investm ent in eq uip-m en t an d the ne ce ssary prelim ina ry surveys?

9. A re you p rep ared to pay particu lar atten tion to train-ing ?

10. D o you know w here you can find techn ical and train-ing sup p ort?


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Recommendations

N ew investm en t m ust alw ays b e p reced ed by a fea sib il-ity stud y. H aving review ed relevant literature a nd takenlocal ad vice , a feasib ility s tud y ab out org anic roofingshou ld aim to g ive clea r an sw ers to the follow ing top ics.A step -by-step ap proach is recom m end ed .

Market and economy

Is the building m arket ab le to a ccom m od ate a n ew or re-

introd uced roofing m ethod?

A nsw ers w ill dep en d on tho rough m arket analysis inc lud -ing , in p articular, the local b uild ing reg ulations. A ke yq ue stion is the m arke t situation. Is it alread y dom inatedb y co m p arab le m aterials, suc h a s co rrug ated iron or con-crete tiles? A survey should be d esigned to interpret thea ttitud es of bu ild ers a nd ho use ow ners. Is the re loc alresistance to re-in trod ucing or m od ifying trad itiona lb iom ass roofing tec hniq ues, an d w hat can b e d one tocha ng e these ide as?

Technical aspects. Materials andequipment

A re the ne cessa ry m aterials available in sufficien t quan -

tity, or is it feasible to grow them or im port them ?

It m ay b e that ag ricultural surp luses or by-prod ucts areinexp ensive , but it is rare that the p rice w ill stay low once

the su p p lier realise s that they a re the b asis for a newind ustry. Feasib ility c alculations m ust assu m e that them aterials supp lier w ill alw ays aim to m axim ise p rofit.

S om e tec hn iq ue s m ay req uire im p ort of m aterials, suc has p rese rva tive s (for w ood tiles), resins o r asp halt (forroo f she ets). In m any co un tries the gove rnm en t m ay re-strict foreig n e xc hang e a llocations for exp orters or forg oo d s d ee m ed to b e of strateg ic im p ortan ce . R oo fingcontractors a re unlike ly to g et p riority in tim es o f sc arcity.

Is eq uipm en t, and sp are p arts availab le?

A lthou g h roofing is lab our inten sive w ork, esp ecially w ith

b iom ass m aterials, p rocessing alw ays req uires som e ca p i-tal eq uipm en t. E ng ine ering skills m ay b e n eed ed to a d ap tha rve sting eq uip m en t (for exa m p le, cerea l ha rve stingequipm ent suitab le for rice or w heat w ill alm ost certainlyha ve to be ad ap ted for cutting tha tch ing g rasse s). M anu-facturing eq uip m ent for asp halt roof sheets is ava ilab lefrom m any d ifferent su p p liers, b ut few w ill have it ava il-ab le off-the-sh elf. Inve stm ent for this technolog y m ust beg uided by very tho rou g h resea rch of b oth the m anufac -turing an d m arketing variab les.

Skills and know-how

A re nece ssa ry skills available?

R oofing w ith b iom ass m aterials ho ld s sig nifica nt ap p ea lfor its e m p loym en t g en erating op p ortun ities . H ow ever,b oth the m aterials p rod uc tion an d sub seq ue nt roo fingw ork is o ften physica lly d em an d ing an d m on oton ou s. If itis p rop osed to try to up g rad e trad ition al tec hn iq ue s, oftha tch ing for exam p le, to m ee t ne w housing exp ec tation s,this m ay require foreig n trainers and possib ly a p eriod ofsu b sid y b efore the ne w tec hn iq ue is integ rated in thelocal construction industry.

B usine ss m an ag em en t skills are a s im portan t as tec hn i-ca l skills bec ause n ew or ad ap ted techn olog ies m ust beco m m ercially viab le.

Further Steps

A nsw ering the ten key q ue stions w ill req uire res ea rchw hich w ill cover m an y issu es: so cio-cultural, ec ono m ic,technical, clim atic a nd geog rap hical, institutional and en-trep reneurial, and the ava ilab ility of skills and kn ow -how .This inform ation form s the b asis for a feasib ility study for:

d evelop ing a strateg y for up g rad ing existing m etho dsof roofing w ith b iom ass m aterials o r, alternative ly,

d eve lop ing a p rog ram m e to introd uce b iom ass roo fingtec hn olog y into a ne w reg ion .


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B uild ing m aterials and co nstruc tion tech nolog iesthat are app ropriate for developing countries, par-ticu larly in the low -inco m e sector, are being de-velop ed , ap p lied and d ocu m ented in m any p artsof the w orld . This is an im portant p rerequisite forp rovid ing safe, d ec ent and afforda ble b uild ingsfor an ever-g row ing p op ulation .

B ut suc h n ew deve lop m en ts ca n d o little to im -p rove the build ing situation, as long as the infor-m ation d oe s not rea ch p oten tial b uild ers. Th etyp es a nd sou rce s of inform ation on stan dard an dinn ova tive b uild ing tec hn olog ies are nu m erousan d very d iverse, m aking ac ce ss to the m diffi-cult.

Th us, in ord er to rem ed y this d raw b ac k, S he lterForum , G ATE , ITD G , S K AT, C R ATerre are co op er-ating in the B uild ing A d visory S ervice an d Infor-m ation N etw ork, w hich co vers five princ ip al sub -jec t area s and c oo rd ina tes the d oc um en tation ,evalua tion an d d isse m ina tion of inform ation .

A ll five grou p s have a co ordina ted d atab ase fromw hich is a vailab le on D ocum en ts, Tech nolog ies,E q uip m en t, Institution s, C onsultan ts as w ell ason P rojec ts and P rog ram s. In a d dition, p rintedm aterial or ind ivid ua l advice on ce rtain sp ec ialsu b jec ts is p rov id ed on req ue st. R ese archp rojec ts, training p rog ram s a nd other field w orkca n b e im p lem en ted in coo p eration w ith loc al or-g aniza tions, if a d istinct need can be identifiedan d the circu m stan ces p erm it.

B A S IN is a se rvice ava ilab le to all institutions andind ivid ua ls co nc erned w ith hou sing , b uild ing an dp lan ning in d evelop ing co un tries, b ut ca n o nlyfunction efficiently if there is a reg ular feed back.

G ATE (G erm an A p prop riate Technolog y Excha ng e) a prog ram m e of the D eutscheG ese llschaft fr Technisch e Z usam m en arbeit (G TZ ) G m b H , ac ts as a ce ntre forthe d issem ina tion an d p rom otion of ap p rop riate tec hn olog ies for de velop ingcountries.

The Interm ed iate Technolog y D evelop m ent G roup (ITD G ) is an ind ep endent B ritishcharity, found ed b y D r. E .F. S chum acher, author of S m all is B eautiful, to h elpinc rea se the inc om e-ge ne rating an d em p loym en t op p ortun ities o f sm all-scaleind ustrial activities in deve lop ing countries.

SK AT (S w iss C entre for D evelop m ent C oop eration in Tech nolog y and M ana ge -m ent) is a d ocum en tation centre and co nsultan cy g roup w hich is engag ed inp rom oting ap p rop riate tec hn olog ies in the Th ird W orld .

B

AS

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UILDING

DVISORY

ERVICE AND

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ETWORK

A d visory Se rvice p rovid ed by W AS/BA SING ATE-G TZP.O .B ox 5180D -65 726 EschbornFed eral R ep ub lic of G erm any

Phone: + 49 - 6196 - 79 3190Fax: + 49 - 6196 - 79 7352e-m ail: hannah .schreckenb ach@ G TZ.D E

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Biomass Roofing Skat