cross-laminated timber-introduction for specifiers

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WIS 2/3-61Wood Information Sheet

Cross-laminated timber:introduction for specifiers

Figure 1: Lenotec cross-laminated timberPhoto: Finnforest

CI/SfBRi2

Uniclass P52:NI

Although cross-laminated (CL) timber is commonly used in Continental Europe, it is a relatively new product in the UK. Yet early applications show that CL timber panel construction can be competitive, even in tall and long span applications where conventional timber framing was hitherto unsuitable or uneconomic.

Made by laminating lengths of timber, CL timber is the main form of solid wood panels (not all solid wood panels are cross-laminated). Wall, floor and roof elements can be pre-cut in the factory to any dimension and shape, including openings for doors, windows, stairs, service channels and ducts. The structures offer high thermal, acoustic and fire performance to satisfy ever-tougher building regulations. CL timber buildings have a very low carbon footprint because the wood locks away the carbon absorbed during growth. Wood is easy to machine and the material itself is a good insulator.

This Wood Information Sheet (WIS) is an overview of the subject with signposts to more detailed sources that are listed at the end. It highlights the design issues that specifiers should consider, except structural aspects that are covered in the companion sheet WIS 2/3-62: Cross-laminated timber: structural principles [1]. WIS 2/3-62 describes how the panels can be assembled into various configurations, the principal connection types and variants, and includes an overview of shrinkage, fire resistance, vibration and disproportionate collapse.

For more detailed guidance on the design of cross-laminated timber structures, refer to GD10: Cross-laminated timber – design guide for project feasibility [2].

Key points

Cross-laminated timber is now being considered where •masonry, concrete and steel have historically been the usual forms of construction.

These large solid structural panels form walls, roofs, floors, •and even lift shafts and stairs.

CL timber improves most of the key performance indicators •promoted by Rethinking Construction.

CL timber panel systems offer the many advantages of •off-site construction.

The panels are made from softwoods with strength grades •in the range C16 to C24.

The panels are suitable for Service Classes 1 (heated •internal) and 2 (unheated internal).

Routes for building services can be provided in the factory, •provided this is planned.

Erection is quick and uses lightweight tools.•

Airtight construction is relatively easy to achieve.•

Due to the large amount of CO• 2 absorbed and stored in the wood, CL timber systems offer enhanced sustainability performance.

Subject: Panel ProductsRevised: March 2011

(2-)

ContentsOverview•

Applications•

Benefits•

Manufacture and •pre-processing off site

Supply•

Configurations•

Hybrid forms•

Erection•

Design principles•



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WIS 2/3-61: Cross-laminated timber: introduction for specifiers

OverviewCross-laminated timber panels (Figure 1) have three, five, seven etc layers stacked on one another at right angles and glued together in a press over their entire surface area. Each layer is composed of softwood boards (of varying lamination thickness) glued together. Sometimes offcuts are used. The build up is symmetrical around the middle layer.

Although it looks like ‘jumbo plywood’, CL timber is a structural product. Panel thickness is in the range 50–300mm, but panels as thick as 500mm can be produced.

There is no current British or European standard for CL timber, but a standard is likely to be published in 2012.

ApplicationsThese large solid panels form walls, roofs, floors, and even lift shafts and stairs. The building envelope can be easily clad with other materials such as timber, brick, mineral render or composite panels. CL timber is now being considered where masonry, concrete and steel have historically been the usual forms of construction.

Although CL timber has a promising future in multi-storey construction (Figure 2), it is likely that low-rise non-residential buildings will be its main application (Figure 3). See the Configurations section for known and potential end-uses.

CL timber is suitable where an internal exposed timber surface offers an aesthetic or acoustic benefit, such as exhibition spaces, places of worship, sports halls, theatres and dwellings.

The practical and current code limit for platform timber frame is seven storeys. In contrast, CL timber is a solid panel, capable of resisting very high racking and vertical loads, and is not limited in height by any building code. TRADA Technology has published a scheme design for up to 12 storeys (see GD10) and feasible building height may increase in the future, subject to consideration of long-term movements.

Figure 2: Apartments with 8-storey CL timber structure at 24 Murray Grove, London

Drawing: Waugh Thistleton Architects

Figure 3: School of the Future at BRE uses CL timber panelsPhoto: Re-thinking (Willmott Dixon)



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Table 1 shows approximate span and height capabilities of the mainstream structural materials.

Material Floor span capability

Height capability

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 20m

CL timber panels 8m for panels 12 storeys

Figure 4 shows how CL timber extends the potential for timber in structures previously possible only in other materials.

020

4060

8010

0H

eigh

t (m

)

5 10Span (m)

Concreteframe

Steelframe

Cross-laminatedtimber Masonry

Platformtimber frame

Benefits

Project outcomesCross-laminated timber improves most of the key performance indicators promoted by Rethinking Construction [3]. CL timber projects have the potential to reduce time and cost, and have predictable outcomes, few defects, few hazards that impact upon health and safety of the workforce and neighbours, high productivity and high level of customer satisfaction. This is largely because the panels are ‘built off site’ under factory conditions and are easily assembled.

It is important to consider the impact that a CL timber structure will have on the entire construction process and the whole-life cost of the building. Detailed comparison with other schemes may show that, when all outcomes are considered, a building with a CL timber structure is quicker, cheaper and safer to build, and has a lower whole-life cost (see WIS 4-31: Life cycle costing [4]).

CL timber structures require no wet trades and are assembled with a crane (needed to lift the panels into place) and lightweight power tools. This presents a low risk of hand-arm vibration injuries.

Fixing decorations and fittings to plain CL timber walls is easier to achieve than with timber frame, concrete or masonry walls.

The relatively low level of noise and disruption on a CL timber site offers advantages on infill sites where the impact on neighbours is an important consideration.

Table 1: Span and height capabilities of mainstream structural materials in multi-storey buildings

Figure 4: Span and height capabilities of mainstream structural materials in multi-storey buildings



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Building servicesThere is no site-cutting of timber elements, provided adequate coordination has been undertaken at design stage. And the installation of building services can be much simplified and, again, done with lightweight power tools.

StructureThe structural benefits are many:

high axial load capacity for walls due to the large bearing area•

high shear strength to resist horizontal loads•

dead weight reduces the need for mechanical holding down to •resist overturning forces

buckling in the plane of the wall is unlikely, except for isolated •columns and piers

contributes to fire resistance•

shallow floors•

structural fixings are easy to provide and likely to achieve their •design capacity

few defects due to the inherent robustness of the panels during •transport and construction

enhanced airtightness•

in some situations, second fix items and cladding can be fixed •directly to panels using lightweight power tools.

Insurance-backed warranties are available.

Figure 5: Lenotec panels in productionPhoto: Finnforest

Manufacture and pre-processing off siteFigure 5 shows a CL timber manufacturing process.

Various adhesives are used to bond together the laminates. Formaldehyde-free panels are available. If glue specification is critical, check with manufacturers.

Panels can be manufactured with their outer layers orientated in either direction relative to the production length (Figures 6 and 7).

When specifying to minimise offcuts and waste, consider the manufacturer’s preferred production sizes and transport limitations.

Figure 6: Orientation of the outer layers transverse to the production length, such as walls

Figure 7: Orientation of the outer layers longitudinal to the production length, such as floors and tall walls

Panels can be up to 20m long and 4.8m wide but transport constraints normally govern panel size. Within the UK, size is generally limited by the length of an articulated lorry and by the need to notify the highway authorities. A maximum length of 13.5m and width of 3m is generally considered practical, but beware of limits dictated by site layout and access. It is also necessary to consult all highway authorities on route through other countries.

Some suppliers offer curved panels with a minimum radius of 8m. Transportation becomes more expensive for curved panels because fewer panels can be stacked on any single load.



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MachiningThe manufacturers have various methods of joining adjacent wall and floor panels on site (see WIS 2/3-62) including rebates, notches and half-lapped joints in the edges of the panels.

Panel rebates and openings are cut by computer numerical controlled (CNC) routers. Manufacturers can incorporate cut-outs for windows, doors, ducts and chases in the factory.

As with all pre-fabricated methods of construction, a design freeze is essential in order to ensure that all openings are correctly incorporated into the panels. Avoid late modifications to openings or additional service runs. Modifying panels on site can be costly and time consuming and may affect their structural integrity.

SupplyCL timber panels are currently imported from Germany, Austria, Switzerland and Sweden but, as the local market develops, a UK plant producing CL timber from local timbers may become viable.

There are at least seven suppliers in the UK (Table 2).

Table 2: Suppliers and products

Supplier Origin Product

B & K Structures Binder HolzAustria

X-LAM

Web: bkstructures.co.uk

Donaldson & McConnell Various Various

Web: donaldsonandmcconnell.co.uk

Eurban Schilliger Holz Switzerland

Crosslam

Web: eurban.co.uk

Finnforest Finnforest MerkGermany

LenoTec

Web: finnforest.co.uk

James Jones & Sons Binder HolzAustria

BBS

Web: binder-jones.co.uk

Kaufmann Mayr-Melnhof KaufmannSwitzerland

BSP crossplan

Web: mm-kaufmann.com

KLH UK KLHAustria

KLH solid timber panels

Web: klhuk.com

Stora Enso UK Stora EnsoAustria

CLT

Web: clt.info

Typical material propertiesProperties vary according to the manufacturer and basic materials.

Wood is normally spruce, but larch and pine may be available. The common strength grades (see WIS 4-7: Timber strength grading and strength classes [5]) for the laminates are in the range C16 to C24 and at least one manufacturer offers ‘glulam’ grades GL24H to GL28H.

Moisture content (MC) at delivery is typically 8–14%.

Designers will find that working stresses are low due to the large cross section (see GD10).

Classification of the surface quality of the panels follows BS EN 13017-1 Solid wood panels. Classification by surface appearance. Solid wood panels. Classification by surface appearance. Softwood [6].

CL timber can be supplied for visible or hidden applications:Standard Grade (or non visible quality) surface is suitable for •lining and typically has top layers corresponding to Class C.

Interior Grade (or residential visible) surface is suitable for •exposed residential internal structure and typically has top layers corresponding to Class AB.

Some manufacturers have a third grade, Interior Grade (or •Industrial visible) surface that is suitable for exposed industrial internal structure and typically has top layers corresponding to Class BC.

Surfaces are supplied either sanded or planed, depending on manufacturer.

The density depends on the timber species and is typically in the range 470 kg/m3 (spruce) to 590 kg/m3 (larch) at 12% MC.

CL timber is inherently more stable than the solid wood elements from which it is made. Fissures due to changes in moisture content are unlikely to appear in Service Class 2 conditions (see Eurocode 5 [7]).



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ConfigurationsCL timber panels have been used in:

structural and non-structural wall elements•

multi-storey structures with or without concrete•

substructure•

solid partitions, with and without linings•

floor (ceiling) elements•

parapet wall elements formed from balloonframed•

wall panel elements•

roof elements•

room-in-the-roof sloping panels•

cantilevered floors, eg balconies•

curved load-bearing structure•

load-bearing lift shafts•

stairs (• Figure 8).

It may also be possible to use CL timber panels as pre-insulated wall and roof cassettes, but care would be needed to avoid damaging the insulation in transit.

Room in the roof construction (see WIS 0-12: Room in the roof construction for new houses [8]) highlights the opportunity for prefabrication. Where a roof is required to have a simple arrangement of continuous ridges and gable ends, a room in the roof can be formed using CL timber panels. A breathable roof underlay and rigid insulation will normally be located above the CL timber panels to give a ‘warm roof’ construction which can be prefabricated as an insulated cassette.

CL timber sloping roof panels are typically supported by external walls or eaves purlins and ridge beams (Figure 9). The CL timber panels must transfer vertical load to the wall plates and purlins and ridge beams using suitably engineered fixings. The ridge beam can be omitted where there is sufficient provision to resist the horizontal thrust of the roof at the eaves using a thrust plate and floor diaphragm. Figure 9: CL timber roof panels supported on ridge beam

Photo: James Jones & Sons

Figure 8: CL timber staircasePhoto: Stora Enso/DMH



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Hybrid forms CL timber and platform frame timber frame can be combined to produce a more efficient structural form.

External non-loadbearing walls comprising highly insulated panelsIn this form, CL timber floor panels span parallel to external walls so that external walls can be highly insulated non-loadbearing ‘infill panels’ (Figure 10). Take care with potential differential movement between the loadbearing and infill panels.

direction of floor span

non-loadbearing panels

Figure 10: Non-loadbearing walls

CL timber floor and roof componentsTimber frame walls or concrete or masonry basements may support CL timber floor slabs where a thin floor section is needed. However for low-rise construction, the increased load-bearing capacity of CL timber wall panels may offer no structural advantage over conventional stud framed walls, but the appearance may be preferred.

For basement construction, a concrete or masonry structure should also be provided below external ground level with the CL timber floor slabs bedded onto mortar and DPC at least 150mm above finished ground level.

Engineered timber floor structuresThese can also be combined with CL timber wall panels where a lightweight floor/roof structure is more appropriate or where an exposed CL timber wall panel is an aesthetic requirement.

Composite Timber/Concrete FloorsCL timber floor slabs can also be used to form wood/concrete composite floors, where the CL timber slab is used as a permanent formwork with horizontal shear transfer between materials being provided shear plates and screws.

Hybrid CL timber productsThese include:

Lenostrand (Finnforest) – a cross-laminated OSB product•

Leno K (Finnforest) – a cross-laminated product containing a •central layer of Kerto laminated veneer lumber (LVL).

ErectionCL timber structures offer reliable on-site programming due to large prefabricated panel elements.

Figure 11 shows typical panel bedding onto a concrete base.

Figure 11: Lowering wall panel onto levelling plates and grout beddingPhoto: Stora Enso/DMH

Where site storage is limited, panels can be delivered to site and erected using a ‘just-in-time’ approach. As panels arrive, a small team of erectors cranes them into position directly from the lorry using preinstalled lifting points (Figure 12).

Figure 12: Panel lifting pointsPhoto: Stora Enso

While installation in wet weather is inconvenient, rain has no immediate effect on the panels as they will dry quickly. Provide protection for panels that are left exposed to weather after erection (Durability and finishes).

Aerial transport may be the most practical in some locations.



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Design principles

Structural design principlesSee WIS 2/3-62.

Incorporating building servicesPanels can incorporate pre-formed service routes for small services such as electrical wiring. These may be routed through the rebates at the interfaces between two adjacent panels or be drilled and rebated into the panels to order. Services may also be routed in chases on the surface of the panels which are premilled into the panels in the factory.

Early coordination with the architect and building services engineer is essential to take advantage of this service.

Alternatively, building services may be routed in a cavity formed by a layer of plasterboard fixed to battens on the face of the CL timber wall or a suspended ceiling supported from the underside of floor panels.

Underfloor heating pipework or other services that run above the floor panel can be accommodated within a screed.

Thermal performanceThermal mass can reduce the variation in temperature over the daily cycle, although other factors such as ventilation, solar gain and insulation must be taken into account. When the design maximises passive solar gain through glazing or from heat generated in the building’s use, the thermal mass of the CL timber can be used to collect and store energy during the day for emission later in the cycle. Important properties are thermal conductivity (rate of transferring heat) and specific heat capacity (ability to retain heat). For example, CL timber and lightweight concrete block materials have a similar thermal conductivity while CL timber has a greater specific heat capacity. Therefore, a 70mm CL timber panel has a thermal mass similar to 100mm lightweight block.

Unlike conventional timber framing alone, CL timber makes a contribution to the U value. For example, a 100mm CL timber panel of density 500 kg/m3 has λ value 0.13 W/mK.

Therefore to achieve the target U value 0.35 W/m2K under the current Building Regulations, a 100mm CL timber panel (with 12mm plasterboard, 25mm service void, 50mm cavity, brick cladding and no thermal bridging) would require 75mm mineral wool insulation or equivalent (Figure 13).

Designers must assess the risk of condensation. A well ventilated cavity and ‘breathable’ insulation will be needed.

AirtightnessThermal performance will be compromised if the construction does not achieve adequate airtightness. Because CL timber construction would not normally include a vapour control layer, the system relies entirely on the detailing of joints to achieve airtightness. Joints that are merely screwed together may suffice but this will depend on ‘true’ surfaces and good workmanship. Airtightness is normally achieved with either pre-compressed foam tape within the joint or breathable tape across the outside joint. Pre-completion testing may be needed to demonstrate compliance.

Acoustic performanceWhen considering sound transmission through party walls, CL timber panels are more similar to lightweight masonry construction (where the mass of the wall contributes to the acoustic performance) than timber frame wall panels (where the layers of plasterboard attached to the panels will provide much of the sound reduction between dwellings).

Consult manufacturers for tests on various configurations. In the absence of test data, it is safe to conclude that CL timber walls with plasterboard (similar to what would be used on timber frame walls) will provide acoustic performance well in excess of what the Building Regulations require. Pre-completion testing may be needed to demonstrate compliance.

When protecting against external noise (which is not covered by the Building Regulations), designers may take account of the acoustic resistance of the CL timber, although the transmission via

50 75 100 25 12.5

cladding

typicaldimensions

cavity

breather membrane

insulation

CL

optionalservice void

plasterboard

Figure 13: Typical section with insulation



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the windows may dominate. Consult manufacturers for tests on various configurations.

CladdingCladding systems for CL timber structures are of three types:

Fixed directly (not self-supporting).• This system would comprise cladding battens and insulation screw fixed directly to the CL timber.

Framed from the CL timber (not self-supporting).• This system also relies on battens to support the cladding but includes a secondary batten within the insulation to support the cladding. A single deep batten is a simple solution but it presents a cold bridging problem. A layered system of battens at right angles (with insulation in corresponding layers) is preferred to minimise cold bridging.

Self supporting.• This system relies on secondary framing (independent of the CL timber wall panel) to transfer lateral loads by spanning between floors and roof levels.

WIS 1-50: Wood cladding for building refurbishment [9], describes cladding systems with external insulation in more detail.

Durability and finishesDurability of CL timber panels will depend on the timbers used for its manufacture and the level of exposure to the weather. WIS 4-28: Durability by design [10] sets out design principles that enhance the durability of timber structures.

Heartwood durability is: for spruce, not durable–slightly durable; for pine, slightly durable–moderately durable; or for larch, moderately durable. Sapwood portions are not durable against fungi or wood boring insects.

Since both sapwood and heartwood are present in CL timber, panels will be liable to decay if their moisture contents exceed 20% for an extended period of time. Therefore, it is important that these timbers are not exposed to continuous wetting by providing a drained and vented cavity behind cladding. Structural timber must be at least 150mm above finished ground level.

CL timber panels are not suitable for long-term external exposure and a separate cladding system is necessary. Consult manufacturers about durability of particular products.

When specifying in situations prone to weathering, follow the principles in WIS 2/3-60: Specifying timber exposed to weathering [11].

CL timber is suitable for service classes 1 (heated internal) and 2 (unheated internal) in Eurocode 5.

Where CL timber is used as an external floor, such as a cantilevered balcony, protect the top and exposed edges with a water-proof membrane.

Protect CL timber panels at ground floor soleplate level using a DPC and/or treated timber.

When specifying exterior finishes of CL timber panels, follow WIS 2/3-1: Finishes for exterior timber [12], taking account of the finish on the panels as supplied.

If panels are to be exposed in service, take care to avoid water staining and mechanical damage during transport, storage and installation, as blemishes can be difficult to rectify.

SustainabilityCheck that the wood used in CL timber panels is from managed, sustainable forests. Manufacturers supply chain of custody certificates under the FSC or PEFC schemes (see WIS 2/3-58: Sustainable timber sourcing [13]).

Using wood from managed, sustainable forests is one of the best ways to reduce a building’s carbon footprint. The Edinburgh Centre for Carbon Management estimates that between 0.7 and 1.1 tonnes of carbon dioxide is saved for every cubic metre of wood used instead of other building materials.

The more wood is used, the nearer the construction moves towards being carbon neutral. Buildings made with solid wood panels in walls, floors and roofs are likely to have a negative carbon footprint. In other words, the carbon absorbed as the trees grow exceeds the carbon associated with all the materials in the building. This is because such large volumes of wood are used in construction. (Note that wood has negative carbon intensity only if the timber is taken from a sustainably managed source.)

The UK Government’s PAS 2050:2008 - Specification for the assessment of the life cycle greenhouse gas emissions of goods and services [14] is a Life Cycle Assessment methodology that can attribute a negative Greenhouse Gas Value to materials that capture carbon, either through their biology or through their chemistry. This means that timber can be described as carbon negative if the amount of carbon captured is greater than that emitted through its lifecycle.



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The locked-in carbon (known as sequestered carbon) may offset some requirements for renewable energy expected by building authorities. This can have a significant advantage because of the space and plant required to accommodate a renewable energy supply.

When the eventual decay of the wood is taken into account, a wood structure will usually have a lower net emission than others. Figure 14 compares the net carbon emitted over the life of timber and other structures.

Car

bon S

tora

geE

mis

sion

Growth Use in structure

Carbon emitted by processingCarbon emitted by combustion or decay

Net carbon emission

Time

The shaded area above the line represents the net amount of carbon emission locked away in the wood stucture.

Cellulose-based structure

Figure 14: Impact of cellulose materials on carbon storage and emission

Over the life of a timber structure, the net amount of carbon locked away is reduced by processing energy during construction and finally by decay or burning in a biomass energy system at the end of its life cycle. The net emission is generally lower than with other materials because the processes for preparing wood and constructing wood buildings are not energy intensive.

An analysis of the total carbon footprint of a building should also take account of the non-renewable energy consumed by users, which will be affected by the thermal performance of the building.

At the end of the building’s life, the CL timber panels may be suitable for re-use or recycling (see WIS 2/3-59: Recovering and minimising wood waste [15]). The untreated wood and the glues used in CL timber panels make the product suitable as a biomass fuel.

Car

bon Sto

rage

Em

issi

on

Extraction Use in structure

Time

The shaded area below the line represents the net amount of carbon emitted by the structure.

Net carbon emission

Non-Cellulose–based structure



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ReferencesWIS 2/3-62: 1. Cross-laminated timber – structural principles, TRADA Technology, 2011

GD10: 2. Cross-laminated timber – design guide for project feasibility, TRADA Technology, 2009

Rethinking construction: the report of the construction task force3. , Department of Trade and Industry 1998

WIS 4-31: 4. Life cycle costing, TRADA Technology, 2008

WIS 4-7: 5. Timber strength grading and strength classes, TRADA Technology, 2011

BS EN 13017-1:2001 6. Solid wood panels. Classification by surface appearance. Solid wood panels. Classification by surface appearance. Softwood, BSI

BS EN 1995-1-1:2004+A1:2008 7. Eurocode 5. Design of timber structures. General. Common rules and rules for buildings, BSI

WIS 0-12: 8. Room in the roof construction for new houses, TRADA Technology, 2003

WIS 1-50: 9. Wood cladding for building refurbishment, TRADA Technology, 2009

WIS 4-28: 10. Durability by design, TRADA Technology, 2004

WIS 2/3-60: 11. Specifying timber exposed to weathering, TRADA Technology, 2008

WIS 2/3-1: 12. Finishes for exterior timber, TRADA Technology, 2005

WIS 2/3-58: 13. Sustainable timber sourcing, TRADA Technology, 2007

PAS 2050:2008 14. Specification for the assessment of the life cycle greenhouse gas emissions of goods and services, BSI

WIS 2/3-59: 15. Recovering and minimising wood waste, TRADA Technology, 2008

Other readingBIP 2181:2008 Guide to PAS 2050. How to assess the carbon footprint of

goods and services, BSI

TRADA TechnologyChiltern House Stocking Lane Hughenden Valley

High Wycombe Buckinghamshire HP14 4ND UK

t: +44 (0) 1494 569600 f: +44 (0) 1494 565487

e: [email protected] w: www.trada.co.uk

About TRADAThe Timber Research and Development Association (TRADA) is an internationally recognised centre of excellence on the specification and use of timber and wood products.

TRADA is a company limited by guarantee and not-for-profit membership-based organisation. TRADA’s origins go back over 75 years and its name is synonymous with independence and authority. Its position in the industry is unique with a diverse membership encompassing companies and individuals from around the world and across the entire wood supply chain, from producers, merchants and manufacturers, to architects, engineers and end users.

Our aimTo provide members with the highest quality information on timber and wood products to enable them to maximise the benefits that timber can provide.

What we doWe seek to achieve this aim through active and on-going programmes of information and research. Information is provided through our website, an extensive collection of printed materials and our training courses.

Research is largely driven by the desire to update and improve our information so that it continues to meet our members’ needs in the future.

Whilst every effort is made to ensure the accuracy of the advice given, the company cannot accept liability for loss or damage arising from the use of the information supplied.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner.

TRADA Technology is contracted by the Timber Research and Development Association to prepare and publish all Wood Information Sheets.


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