JURNAL 3

Architecture Construction and Industrialization,

Coursework 1

A sustainable approach to materials and

construction systems: Engineered Timber

Andrea Botti

MSc Advanced Sustainable Design, year 2011/2012

Edinburgh School of Architecture and Landscape Architecture

University of Edinburgh

A sustainable approach to materials and construction systems: Engineered Timber [1]

University of Edinburgh MSc Advanced Sustainable Design, year 11/12

Table of contents

Table of contents ........................................................................................................................ 1

1. Timber: traditionally sustainable .......................................................................................... 2

2. Ecological impact of timber and other construction methods ............................................... 3

3. From tradition to innovation: engineered timber ................................................................... 5

4. Ecological impact of engineered timber products and wood-based panels ........................ 17

5. Contemporary use of timber .............................................................................................. 22

6. Case studies ..................................................................................................................... 25

7. References ........................................................................................................................ 27



1. Timber: traditionally sustainable

The Italian architect Matteo Thun claims that wood is the material of the 21st century, and, as

the sole regenerable material used in architecture and design, one could hardly imagine being

without it (Thun, 2010, p.554).

It seems hard to disagree with him, since it is acknowledged that wood is the oldest and the

most widely used building material. It can be found almost everywhere in the world, and its

characteristics make it suitable to be used in a broad range of applications.

Around a third of Europes total land area is covered in forests; the figure is around 16% in

Scotland, with predominance of species such as Sitka Spruce and Scots Pine (Wilson, 2001).

Softwoods Hardwoods

Sitka Spruce Pines (mainly Scots Pine, but also Lodgepole and Corsican) Larches (mainly European and Japanese) Douglas Fir Norway Spruce

Oaks (pedunculate and sessile) Beech Sycamore Ash Elm Birch

Table 1. Most common commercial tree species in Scotland (adapted from Wilson, 2001).

One of the greatest aspects of timber is that it is a renewable resource: if the wood resource

comes from sustainably managed forests, it will be available indefinitely. Thanks to sustainable

forestry practices, Scotland, for instance, is growing more timber than it harvests (Wilson 2001).

As we engage with a sustainable agenda, it seems appropriate to carefully evaluate a

construction material whose environmental benefits are matched by few others. The Edinburgh

Centre for Carbon Management estimates that for every cubic metre of timber used instead of

other building materials, between 0.7 and 1.1 tonnes of carbon dioxide is saved (TRADA

Technology, 2008, p.9).

The aim of this report is to provide a review on the whole range of derivative timber products, to

which we can inclusively refer to as engineered timber, with regards to their sustainability

potential. With this scope, a comparison of the ecological impact of timber structures with other

construction methods namely steel and concrete is reported in first instance.

After an overview of the engineered timber products and their general characteristics, the report

focuses on how those products behave environmentally, according to their degree of technology

and processing from the original material - wood. An overview of the products assessment and

application in sustainable construction is presented. In the last section, some observations on

the role of timber in contemporary architecture, more specifically on how engineered timber

applies to modern methods of construction and reusable/adaptable structures, are followed by

two case studies that are representative of the novelty of application.



2. Ecological impact of timber and other construction methods

Comparative analysis is probably the most effective means to assess the ecological footprint of

different construction methods. The short summary here presented includes seven different

Life-Cycle Assessment studies on residential buildings, that compared timber frame with

alternatively steel and concrete structures in terms of energy use and green-house gas

emissions (the latter expressed as Global Warming Potential, or GWP) (Eriksson, 2004).

Cradle to gate

Recyclable energy

Total energy use excluding usage phase

GWP (CO2 equivalent)

1 Environmental Assessment of Trhus 2001, Trtek

Trhus 2001 960 1460 -530 30

Concrete design 2260 490 1770 400

2 Residential Case Study, Athena Sustainable Material Institute

Wood design 1140 280

Steel design 1740 - - 340

Concrete design 2520 - - 420

3 Environmental Impact of a Single Family Building Shell, Minneapolis

Wood design 969 n/a - 207

Steel design 1604 n/a - 309

4 Environmental Impact of a Single Family Building Shell, Atlanta


Steel design 810 n/a - 170

5 Environmental and Energy Balances of Wood Products and Substitutes, ECEFAO


Brick design 1090 n/a - 840

6 Energy Use and Environmental Impact of New Residential Buildings, Lund Institute of Technology

Wood design 4540 2160 2380

Concrete design 3020 1120 1900

7 LCA of Building Frame Structures Environmental Impact over the Life Cycle of Wooden and Concrete Frames, Chalmers Univ. of Technology


Concrete design 1430 n/a - 110

Table 2. Results summary for LCA studies (data retrieved from Eriksson, 2004).



The results of comparative analysis are clear: timber frame structures perform significantly

better, with respect to energy use and GWP. In order to reasonably quantify the differences

between the cases, the boundaries for the LCA cases were divided into four categories, as

indicated below.

- Excluding energy recycling - Including wood feedstock energy

- Including energy recycling - Including wood feedstock energy

- Excluding energy recycling - Excluding wood feedstock energy

- Including energy recycling - Excluding wood feedstock energy

1 Case 1a Case 1b

2 Case 2

3 Case 3

4 Case 4

5 Case 5a Case 5b

6 Case 6a Case 6b Case 6c

7 Case 7a Case 7b

Figure 1 Energy usage differences between timber, steel and concrete structures (adapted from Eriksson, 2004).

Figure 2 GWP differences between timber, steel and concrete structures (adapted from Eriksson, 2004).

0

500

1000

1500

2000

2500

1a 1b 2 3 4 5 6a 6b 6c 7a 7b

Energy difference (MJ/m2)

Steel - Wood Concrete - Wood

050100150200250300350400

1a 1b 2 3 4 5a 5b 6 7

GWP difference (Kg/m2) - CO2 equivalent

Steel - Wood Concrete - Wood



3. From tradition to innovation: engineered timber

The development of engineered timber has been historically related to economic advantages.

Investigation and research on ways and means of using the wood more efficiently has generally

been considered to be driven by the increasing cost of sawn timber and green logs.

Despite constantly increasing their efficiency, sawmills still produce considerable amounts of

residues - from 35% of each log - in forms of low grade logs or thinnings, chips, slabs and

sawdust (see table 3); those can be used to manufacture many kinds of wood-based panels.

Tree part or product Portion (%)

Left in the forest:

Top, branches and foliage 23

Stump (excluding roots) 10

Sawdust 5

Sawmilling:

Slabs, edgings and off-cuts 17

Sawdust and fines 7.5

Various losses 4.0

Bark 5.5

Sawn timber 28

Total 100

Table 3. Division of a typical tree harvested for sawn timber (source FAO).

While that is certainly true, it would be it quite reductive to consider the technological progresses

on timber solely in terms of economic savings. To respond to a need of diverse applicability and

improved performance, the construction industry has identified manifold technical reasons to

guide the application of engineering processes onto sawn timber and overcome its

shortcomings.

Mechanical properties

Wood is an orthotropic material, having unique and independent mechanical properties i.e.

elastic, strength, vibration properties - in the directions of three mutually perpendicular axes:

longitudinal (fibres direction), radial and tangential. Moreover those differ greatly from species to

species. Engineered timber products offer more homogeneous properties and consequently

they find much wider application in a variety of building elements (Kretschmann, 2010).

Dimensional limitations

They are part of its nature and are counted as weaknesses only in comparison with materials,

such as steel and concrete, that offer considerable structural spans.



Performance, structural properties and dimensional stability

Direction to grain or board length

Parallel (%) Perpendicular (%) Thickness (%)

Solid timber

Douglas fir negligible 2.0-2.4 2.0-2.4

Beech negligible 2.6-5.2 2.6-5.2

Plywood

Douglas fir 0.24 0.24 2.0

Particleboard

UF bonded 0.33 0.33 4.7

PF bonded 0.25 0.25 3.9

MF/UF bonded 0.21 0.21 3.3

Fibreboard

Tempered 0.21 0.27 7-11

Standard 0.28 0.31 4-9

MDF 0.24 0.25 4-8

Table 4. Dimensional stability of timber and boards. Change in dimensions from 30% to 90% relative humidity (adapted from Dinwoodie, 2000).

Bending Strength (MPa)

Bending Stiffness (MPa)

Thickness (mm)

Density (kg/m3)

par. per. par. per.

Solid timber

Douglas fir 20 500 80 2.2 12700 800

Plywood

Douglas fir 4.8 520 73 16 12090 890

Douglas fir 19 600 60 33 10750 3310

Particleboard

UF bonded 18.6 720 11.5 11.5 1930 1930

PF bonded 19.2 680 18.0 18.0 2830 2830

MF/UF bonded 18.1 660 27.1 27.1 3460 3460

Fibreboard

Tempered 3.2 1030 69 65 4600 4600

Standard 3.2 1000 54 52 - -

MDF 9-10 680 18.7 19.2 - -

Table 5. Strength properties of timber and boards (adapted from Dinwoodie, 2000).

Optimise the use of the renewable resource

The manufacturing processes of wood-based panels use a very high percentage of the initial

log through thinnings, chips, slabs - thus making full use of the resource and minimising waste

(Thoemen et al., 2010).



Engineering wood products can be divided in four main categories:

1. Structural Timber Composites

Double and triple laminated beams

Glued laminated timber

Parallel strand lumber

2. Laminates

Cross Laminated Timber

Solid wood panel

Laminated Veneer Lumber

Plywood

3. Fibre composites

Hardboard

Softboard

Fibreboard (MDF)

4. Particle composites

Oriented Strand Board (OSB)

Wood particleboard (or chipboard)

Cement-bonded particleboard

Laminated Strand Lumber (LSL)

Figure 3 Various composite products derived from timber (Stark et al., 2010).



Double and triple laminated beams (Duobeams and Triobeams)

They consist of two or three timber lamellae, rigidly

bonded together after visual or machine strength

grading. After being glued, they are side-dressed and

chamfered on 4 sides. Individual lamellae can be

finger-jointed. (HFA, OG 2010b)

Glued laminated timber (Glulam)

Glued laminated timber is manufactured from

laminates of sawn timber, or lamellae, kiln dried,

planed and glued together with parallel fibre

orientation.

The process of finger jointing allows individual

laminates to be end-jointed to produce long lengths.

High resistance and dimensional stability properties

make glulam particularly suitable for elements bearing

high stresses or spanning large distances. The choice of the adhesive has to be accurate in

order to fulfil the European standard requirements for loadbearing timber components. (HFA,

NEU 2010b)

Parallel strand lumber (Parallam)

It is manufactured from 3 mm thick and 15 mm wide

strips of veneer, bond together with phenolic resin.

The strips are bundled with fibres oriented primarily

parallel to the major axis of the beam. They are

processed in a continuous press to form an endless

beam.

Parallel strand lumber is designed to be used in

structures with long free spans. PSL elements can be

bonded together, to obtain components with large

cross-sections. (HFA, NEU 2010c)

Figure 4 (HFA, OG 2010b)

Figure 5 (HFA, NEU 2010b)

Figure 6. (HFA, NEU 2010c)



Cross Laminated Timber: a deeper look

Cross Laminated Timber (CLT) consists of several

layers (3, 5, 7 or more) of softwood timber planks,

also called lamellas, joined with glue or through

dowels. The directions of the grain of adjacent

planks form an angle of 90, with a symmetrical lay-

up around the middle layer. Planks may be joined by

edge-gluing and may also be finger-jointed in the

longitudinal direction.

CLT is now being considered where masonry, concrete and steel have historically been the

usual forms of construction, presenting some key advantages:

it is dimensionally stable, solid and capable of resisting very high racking and vertical loads,

extending the potential of timber in structures previously possible only in other materials

(see Table 1). Furthermore, its combination of strength, ductility and light weight makes it an

excellent construction system for anti-seismic buildings;

it eliminates the main disadvantages connected with normal wood construction, such as

swelling, shrinkage, warp, and creep;

short assembly time at the site, with consequential economic benefits, since it is

manufactured off-site, under factory conditions and with efficiency automation;

it can be standardised to be used for ceilings, roofing or walls or can be designed for tailor-

made components of the entire buildings (big companies like RikoHaus and Rubner produce

catalogues of tailor-made prefabricated wooden houses);

good thermal properties: unlike conventional timber framing alone, CLT makes a

contribution to the U value. It has similar thermal conductivity and greater specific heat

capacity than lightweight concrete block materials;

high thermal mass; when the design maximizes passive solar gain, CLT is suitable to be

used to collect and store energy during the day for emission later in the cycle;

very good acoustic insulation;

because its manufacturing process consumes low amounts of electricity, CLT has very

favourable ecological assessment. Overall the utilization of adhesives is very limited, which

also reduces the total impact on the environment. Formaldehyde-free panels are largely

available on the market.

(HFA, NEU 2010a; TRADA Technology, 2011)

Figure 7 (HFA, NEU 2010a)



Material Floor span capability Height capacity

Steel 7m for metal deck floors > 100 storeys

Concrete 9m for solid slabs > 100 storeys

Masonry 7.5m for hollow core floor 7 storeys

Platform timber frame 6m for engineered timber joists 7 storeys or 20 m

CLT panels 8m for panels 12 storeys

Table 6. Span and height capabilities of mainstream structural materials in multi-storey buildings (TRADA Technology, 2011)

Solid Wood Panel

It is a multi-layered board, with a symmetric lay-up

consisting of parallel outer layers and at least one core

layer, oriented perpendicularly to them. The individual

lamellae are sorted, planed prior to their assembly into

the boards, thus minimising swelling and shrinkage

due to climatic changes (HFA, OG 2010g).

Laminated Veneer Lumber (LVL)

LVL is manufactured in a continuous process, that

consists in bonding individual - spruce or pine

veneers with their individual ends offset and with fibres

primarily in the same direction. PF resins are generally

used as adhesives.

LVL finds application as bracing element in load-

bearing floors and ceilings, and can be used in the

same applications as glulam (HFA, OG 2010c).

Figure 8 (HFA, OG 2010g)

Figure 9 (HFA, OG 2010c)



Plywood

Veneer plywood

Plywood is a panel consisting of an assembly of layers

glued together, usually odd in number (3, 5 or 7) and

not exceeding 7 mm in thickness. Each veneer is laid

down with its grain at right angles to the adjacent

layer, and all the veneers are orientated with their

plane parallel to the surface of the panel. Plywood is a

very versatile product: it offers high strength to weight

properties and it performs well under severe exposure conditions; the choice of the adhesives

for its manufacturing determines the panels suitability for internal or external use.

Four types of plywood are commonly available in the UK: marine plywood (BS 1088), structural

plywood, utility plywood, decorative / overlaid plywood.

Production varies depending on several factors, but it usually includes the following sequence of

processes:

Log conditioning

Peeling

Clipping

Drying

Jointing or veneer repair

Grading

Adhesive application

Pressing

Trimming, filling and sanding

Core plywood (Blockboard / Laminboard)

Blockboard uses for its core strips of wood, each not more than 30 mm wide; laminboard cores

are composed of strips of veneer on edge (or occasionally strips cut from plywood). The strips

are laid separately and glued or otherwise joined together to form a slab. One or more veneers

is glued to each face with the direction of the grain of the core strips running at right angles to

that of the adjacent veneers.

Introduction of block or laminboard manufacturing facilities by ply mills is aimed to utilise

residues to produce low cost types of panel suited to interior purposes. The technique of

manufacturing core plywood developed alongside the plywood industry from the turn of the

century and the method of production is similar to that for plywood.

(HFA, OG 2010f; TRADA Technology, 2003; Thoemen et al., 2010)

Figure 10 (HFA, OG 2010f)



Fibreboards

They are manufactured from fibres of ligno-cellulosic

material. According to the manufacturing process, they

are divided into two main categories: wet process and

dry process boards.

Wet process boards

Generally produced without the addition of a synthetic resin; the primary

bond derives from the felting of the fibres and their inherent adhesive properties.

The boards are classified according to their density:

Hardboards: > 900kg/m3

Mediumboards: 400kg/m3 < < 900kg/m3

Softboards: 230kg/m3 < < 400kg/m3.

The production process is essentially as follows:

Chipping

Reduction to fibres

Board (wet lap) forming

Pressing and curing (hardboards and medium boards)

Curing insulating board

Finishing

(TRADA Technology, 2003; Thoemen et al., 2010)

Dry process boards

The dry process was developed from the traditional wet process and the fibre is produced in the

same way. However, an adhesive is added to the fibres and they are dried to below 20%

moisture content before mat forming and pressing. Differences in the production process are:

Resin application

Drying / storage

Mat-forming

Pressing

Trimming and sanding

Figure 11 (HFA, OG 2010d)



Medium density fibreboard (MDF)

In MDF the fibres of ligno-cellulosic material are felted together with the primary bond normally

derived from a bonding agent. The properties of the material can be modified or enhanced by

changing the composition of the synthetic binder or by incorporation of other additives during or

after manufacture.

MDF is the most common dry process board. The particular machining and finishing attributes,

combined with good working properties and a wide range of available sheet thicknesses and

sizes allow MDF to find multiple applications in construction, e.g. skirtings, architraves, window

boards, wall linings and decorative facades.

(HFA, OG 2010d; TRADA Technology, 2003; Thoemen et al., 2010)

Oriented Strand Board (OSB)

OSB is a multi-layered wood-based composite, with

each layer made from long slender wood strands

bonded by a polymeric adhesive. Similarly to plywood,

the strands are orientated in each layer in the main

axis of the board. Due to the high aspect ratio of the

strands (length to width up to 10:1), the board's

bending strength is particularly high in the direction of

the strand.

Oriented Strand Boards are widely used for wall sheathing, flooring underlays, roof sheathing

and decking. Four classes of boards are defined according to BS EN Standards, serving from

general purpose to heavy duty load-bearing for use in humid conditions. However they are not

recognised in the standards as being suitable for exterior use.

The process of producing wood strands and of aligning them along the length of the board was

developed during the 1970s in Germany and replaced the original waferboard production. OSB

manufacture has many similarities with that of particleboard. It includes:

Debarking

Waferising, strand cutting and drying

Blending

Mat forming

Pressing

Trimming, conditioning and sanding

(HFA, OG 2010e; TRADA Technology 2003; Thoemen et al. 2010)

Figure 12 (HFA, OG 2010e)



Wood particleboard (or chipboard)

Wood particleboard is manufactured from small wood

particles or particles from lignocellulosic raw materials

and a binder (usually a synthetic resin). The particles

are not aligned in a particular way, but generally

oriented parallel to the plane of the board. It is usually

referred to in the UK as chipboard.

Boards can be of uniform construction, of graded

density or of distinct 3 or 5-layer construction. Their

final thicknesses vary from 3 to 50 mm.

The European Standard (BS EN 312) defines six categories of boards, according to their

suitability: from furniture to loadbearing types and humid interior conditions.

The production of wood particleboard originated in Germany at the beginning of the 20th century,

following the discovery of synthetic thermo-setting adhesives. It entails mechanically breaking

up wood mostly green logs - and reconstituting it by the means of the adhesives.

The process is usually highly automated and is not very demanding in terms of raw materials

and skilled labour (unlike, for instance that of plywood).

The basic stages are:

Debarking

Chipping or milling (often from green logs, but at the present time increasing levels of

recycled timber are being used)

Drying

Sifting / particle classification

Glue blending

Mat forming

Pressing

Trimming and sanding

Extruded Particleboard

(HFA, OG 2010h; TRADA Technology, 2003; Thoemen et al., 2010)

Figure 13 (HFA, OG 2010h)



Cement-bonded particleboard

Cement-bonded particleboard is a wood composite

consisting of small wood particles and a mineral

bonding agent (e.g. Portland or magnesite cement).

Boards are manufactured as single-layered or multi-

layered and also as sandwich composites (e.g. in

combination with rigid foam or cork insulation boards).

Boards density can vary according to finality; they can

be used for thermal and acoustic insulation, as internal

walls or load-bearing and bracing panelling.

Thanks to the mineral content, cement-bonded particleboard offer a superior behaviour in fire

and are suitable for exterior use: they are highly resistant to weathering, insects and fungi.

The production is quite different from other particleboards, because wood content is low (20-

30% by weight) and the boards are pressed at a relatively low temperature. It includes the

following stages:

Raw materials

Flaking and milling

Sifting / screening

Blending and forming

Pressing and curing

Trimming, maturing / conditioning

(HFA, OG 2010a; TRADA Technology, 2003; Thoemen et al., 2010)

Figure 14 (HFA, OG 2010a)



Structural Insulated Panels (SIP)

Structural Insulated Panels are prefabricated lightweight building units. They combine

engineered timber with rigid foam, thus providing structural support and thermal insulation in

one system.

They are sandwich panels made of:

face layers

core layer 70 to 250mm

face layer

Two high density face layers, e.g.:

- oriented strand boards, such as OSB

- cement particle board

with thicknesses of 8 to 15mm.

A central core of rigid cellular insulation e.g.:

- Polyurethane (PUR) - Polyisocyanurate (PIR) - Phenolic foam (PF) - Expanded polystyrene (EPS) - Extruded polystyrene (XPS)

Like other massive timber elements, SIPs can serve as walls or roof.

They are usually manufactured off-site, due to the fact that a high quality standard of production

is needed to meet their performance requirements.

Two different fabrication techniques exist:

1. The foam core is pre-cut and is cold pressed between two facing OSB boards, after the

application of the adhesive.

2. The foam is poured into pre-spaced facing, thus binding them together.

SIPs are often employed as principal loadbearing components and are currently used in

domestic and light industrial construction of up to three storeys. SIPs are a very interesting

modern method of construction; thanks to their characteristics they can meet markets pressing

demands for thermal efficiency and speed of construction. (Hairstans, 2010; BRE, 2004)



4. Ecological impact of engineered timber products and wood-based panels

Figure 15

Figure 16

Figure 17

Figure 18. * values take into account the storage of carbon in wood

145447628

166022442538

45425214

236125802403

31372409

Duo&Trio, sawn, air-driedDuo&Trio, sawn, kiln-driedDuo&Trio, planed, kiln-dried

Glue laminated timberCLT (UF adh)CLT (PF adh)

Plywood (UF adh)Plywood (PF adh)

OSB (MUPF/PMDI adh)OSB (PF adh)

Particleboard dryParticleboard humid

Cement-bonded p.board

Abiotic resource [g Sb eq]

6071

120210

310307

358353

265269

156158

88







Photosmog [g C2H2]

206895

202236271

459538

296250

206270

804







Global Warming Potential [kg CO2 eq]

-775-728-701

-571-810-775

-504-424

-740-786

-875-788

281







Global Warming Potential [kg CO2 eq]*



Figure 19

Figure 20

Figure 21

Figure 22

Figures 15-22 show the assessment of ecological impact for engineered timber products (collected and adapted from IB, 2002).

144344

649175016741818

32883612

25681983

17221960

2586







Acidification [g SO2 eq]

1732

70173

148148

298297

177172

149149

256







Over-fertilization [g PO4 - eq]

30810121381

333546025339

939211115

48685476

49047738

4397







PEI non-renewable [MJ]

87409293

1212519640

2174221740

2740627402

1738217367

1359312103

6346







PEI renewable [MJ]



It is relevant to look more in detail at the Global Warming Potential, expressing the percentage

contributions of each process. This represents quite effectively the level of technology

embedded in each wood-based product, and consequently it can reveal how manufacturing

processes affect the ecological footprint of engineered timber.

Figure 23 Chart showing the GWP potential for wood-based products (collected and adapted from IB, 2002).

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Glue Laminated Timber

Cross Laminated Timber

Plywood (PF adh)

OSB (MUPF/PMDI adh)

Particleboard P5 (PF adh)


Breakdown of GWP contributions

Other

Transport

Electric Energy

Thermal Energy

Adhesives

Raw materials



1.5

2

1

0.5

0

-0.5

-1

sawn timber

(65% moisture)

sawn timber

(12% moisture)

structural solid timber

softwood (15% moisture)

laminated beamssoftwood(12% moisture)

glue-laminated timbersoftwood (12% moisture)

three-ply board

OSBplywood chipboard P2

technology input

glob

al w

arm

ing

pote

ntia

l [K

g C

O2

equi

vale

nt]

wood-cementboard

MDF

Figure 24 Chart showing the GWP potential for wood-based products (adapted from Hartwig et al., 2009).

As indicated on the charts, it can be stated in conclusion that the more processed is timber, in

manufacturing engineered products, the higher the loss of ecological benefits - in terms of LCA

and GWP - associated with its native properties. This challenges the popular idea that wood-

based products can be universally sustainable, regardless of their application in construction

(see table 7).



Material / application Columns / beams

Load-bearing/ planking

Dry screed

Interior finish

Furniture Ecological Assessment

Solid wood panel

o o -

favourable

Low to moderate potential impact in most environmental criteria. Considerable energy consumption during the kiln drying of timber. The product is untreated product and has a low proportion of binding agent.

Glue-laminated timber

+

gen. favourable, weaknesses

exist

Low impact in most of the environmental criteria, although the substantial amounts of electricity consumed during the manufacturing process result in a high acidification potential. Use of adhesives is relatively low.

Veneer plywood; Blockboard/Laminboard o o + +

medium favourable

Manufacturing process of veneers is energy intensive, esp. with regards to electrical energy. Adhesives are used in a high proportion and form an important part of the product; they further contribute to the total environmental impact.

Laminated veneer lumber - -

medium favourable

High potential impact in most of the environmental criteria assessed, due to a very energy intensive manufacturing process; adhesives contribute to total impact.

Laminated flat-pressed board + + o -

gen. favourable, weaknesses

exist

Low impact in most of the environmental criteria, although it presents high acidification potential. The relatively high use of adhesives contributes to the total environmental impact, since they might contain formaldehyde.

Cement chipboard

o o o

medium favourable

Very high potentials in GWP, acidification and over-fertilization. The high energy consumption in the manufacture of the binding agent (cement) contributes significantly to the overall impact. Boards are not recyclable.

Oriented strand board (OSB) + + o

favourable, weaknesses

exist

Low to moderate potential impact in most of the environmental criteria assessed, thanks to a moderate utilization of adhesives. Nevertheless the manufacturing involves a considerable consumption of electrical energy.

Medium-density fibreboard (MDF)

- - medium favourable

Made from thinnings. High proportion of adhesives that might contain formaldehyde.

+: low environmental impact o: low environmental impact - : high environmental impact, compared to other products.

Table 7. Applications and environmental assessment for wood-based products (Hartwig et al., 2009; IB, 2002).

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