Timber is a versatile and high performance construction material that can be produced in most parts of the UK. ‘Sustainable construction timber’ has been written to help building designers and contractors source and specify local timber products. The report explains why local sourcing of timber is important, reviews the range of timber species and products currently obtainable in the UK and explores the ways in which local sourcing can be achieved within a construction project. Sustainable construction timber is applicable to designers and contractors wanting to source and specify UK grown timber products, people considering using their own timber on a construction project and those involved in building refurbishment or conservation. Research Report Sustainable construction timber Sourcing and specifying local timber Silvan House 231 Corstorphine Road Edinburgh EH12 7AT £13.00 www.forestry.gov.uk 1199964_Cover_Spread.indd99964_Cover_Spread.indd 1 119/04/20169/04/2016 117:517:51 1199964_Cover_Spread.indd99964_Cover_Spread.indd 2 119/04/20169/04/2016 117:517:51 Research Report Sustainable construction timber Sourcing and specifying local timber Ivor Davies European Union European Regional Development Fund Investing in a Smart, Sustainable and Inclusive Future Forestry Commission: Edinburgh 1199964.indd99964.indd i 118/04/20168/04/2016 08:4808:48 © Crown Copyright 2016 You may re-use this information (not including logos or material identifi ed as being the copyright of a third party) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence, visit: www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team at The National Archives, Kew, London TW9 4DU, or e-mail: [email protected]. This publication is also available on our website at: www.forestry.gov.uk/publications First published by arcamedia in 2009. This second edition published by the Forestry Commission in 2016. ISBN: 978-0-85538-945-1 Davies, I. (2016). Sustainable construction timber: sourcing and specifying local timber. Forestry Commission Research Report Forestry Commission, Edinburgh. i-vi + 1-54 pp. Keywords: construction, local sourcing, specifi cation, sustainable, timber, UK grown. FCRP025/PURE/MLG-1K/APR16 Enquiries relating to this publication should be addressed to: Forestry Commission Silvan House 231 Corstorphine Road Edinburgh EH12 7AT 0300 067 5000 [email protected] The author can be contacted at: Centre for Wood Science and Technology Edinburgh Napier University Merchiston Campus 10 Colinton Road Edinburgh EH10 5DT [email protected] Acknowledgements Producing this second edition of Sustainable Construction Timber would not have been possible without the support of Forestry Commission Scotland, Historic Scotland and the European Regional Development Fund (ERDF) through the East of Scotland European Partnership. The author is grateful for the advice and comments received from: John Alexander (Acsys Technologies), Gordon Callander (James Callander & Son), Dave Cook (Scottish Procurement Directorate), Roger Curtis (Historic Scotland), Stuart Goodall (Confor), Robert Hairstans (Edinburgh Napier University), Paul Hands (James Callander & Son), Alastair Kerr (Wood Panel Industries Federation), John Kissock (formerly of James Jones & Sons), Andy Leitch (Forestry Commission Scotland), Ian Pirie (James Jones and Sons), Una Lee (The Highland Council), Neil May (Natural Building Technologies), Paul McLean (Forest Research), Chris Morgan (Locate Architects), Derek Nelson (Forestry Commission Scotland), Dan Ridley-Ellis (Edinburgh Napier University), Steven Streets (formerly of UK Timber Frame Association), David Sulman (UK Forest Products Association), Deb Turnbull (Edinburgh Napier University) Mark Williams (HRI Architects), Peter Wilson (Timber Design Initiatives) and John Wood (Edinburgh Napier University). Unless otherwise acknowledged, all photographs are by Edinburgh Napier University staff or from the Forestry Commission picture library. The Forestry Commission will consider all requests to make the content of publications available in alternative formats. Please send any such requests to: [email protected]. Cover image: Scottish grown larch cladding on Culloden Battlefi eld Visitor Centre, near Inverness. Designed by Hoskins Architects. Photograph courtesy of Andrew Lee. ii 1199964.indd99964.indd iiii 118/04/20168/04/2016 08:4808:48 Contents Introduction 1 What is a timber building? 3 UK forestry and forest products 5 Sourcing and specifying UK timber 7 How to achieve fi tness for purpose 7 Design within constraints 7 Know who sells what to whom 10 Ensure the timber is legal and sustainable 11 Begin the procurement process as early as possible 11 Ensuring appropriate moisture content 13 Moisture content 13 Fibre saturation point 13 Equilibrium moisture content 13 Timber drying 14 Dimensional change 16 Shrinkage and movement 16 Construction detailing 17 Structural timber 18 Strength variation in timber 18 Strength grading 18 Strength classes 20 Strength classes of UK timber 21 Specifying UK grown strength graded timber 22 Growth rate and density 22 Service classes 22 Fire performance 24 Reaction to fi re 24 Fire resistance 26 Cavity fi res 26 Resistance to wood destroying organisms 27 Fungal decay and insect attack 27 Use classes 27 Natural durability 27 Durability classifi cation 28 Preventing biodeterioration 29 Timber in repair and refurbishment work 32 History of timber use in the UK 32 Selecting the appropriate timber for repairs 33 Moisture content of timber used in repairs 34 Grading structural timber in-situ 34 iii 1199964.indd99964.indd iiiiii 118/04/20168/04/2016 08:4808:48 Hygrothermal materials 35 Assessing moisture risks in existing buildings 36 Sourcing and processing timber yourself 38 Appropriate design 38 Log conversion 38 Strength grading 39 Drying 39 Machining 39 Resistance to wood destroying organisms 39 References 40 British Standards 41 Appendix 1: Carbon impacts of timber 43 Carbon storage 43 Embodied energy 43 Appendix 2: CE marking and local timber 45 Appendix 3: Timber sizes produced in the UK 46 Sizes of softwood sawn timber 46 Sizes of visually graded timber 46 Sizes of external cladding timber 46 Appendix 4: Substituting UK timber for imports 47 Appendix 5: Ensuring timber is legal and sustainable 48 European Union timber regulations 48 Placing UK timber on the European market 48 Forest certifi cation schemes 49 Timber procurement in the private sector 49 Timber procurement in the public sector 49 Appendix 6: Sources of further information 52 iv 1199964.indd99964.indd iivv 118/04/20168/04/2016 08:4808:48 Introduction Timber is a versatile and high performance construction • Minimising the carbon footprint of construction: timber material: is almost carbon neutral, has low embodied energy and can store carbon in the fabric of the building. • It has a high strength to weight ratio. • It is easily shaped and fastened. • Supporting the local economy: the use of locally sourced • It is available in a wide range of colours, textures, material supports a region’s woodland managers, timber densities and chemical compositions. processors and manufacturers. • It can be readily treated or modifi ed to increase its resistance to biodeterioration. • Helping local woodland management: income from timber • At the end of its initial service life it can often be reused sales helps support woodland management and expansion, or recycled. responsible management benefi ts wildlife and increased use of UK timber encourages more planting of trees. Timber is also renewable. This means that – uniquely among mainstream construction materials – it can be produced in • Stimulating timber demand: government policy in the most parts of the UK (Figures 1 and 2). UK – and particularly in Scotland – involves a signifi cant expansion of forest cover and, in order to achieve the targets In addition to a growing recognition of the immediate set, demand for timber products will have to increase. performance benefi ts of timber construction, the material’s popularity is also being driven by an increasing awareness of Finally, let us not forget that knowledge of where the timber climate change and the environmental consequences of has originated from can generate additional interest in a development. Accordingly, government policies supporting building’s design. timber construction span planning, forestry, sustainable development and climate change. Examples of where timber – and particularly local timber – can contribute to achieving these policies include: Figure 1 The headquarters building for Scottish Natural Heritage in Inverness uses locally sourced larch for the external cladding and solar shading. Keppie Design. Courtesy of Michael Wolchover. 1 1199964.indd99964.indd 1 118/04/20168/04/2016 08:4808:48 Figure 2 UK grown Douglas fir is used to spectacular effect in the roof trusses of Grizedale Forest Visitor Centre by Sutherland Hussey Architects. Courtesy of Sutherland Hussey Architects. 2 1199964.indd99964.indd 2 118/04/20168/04/2016 08:4808:48 What is a timber building? In the UK, the term timber frame describes a construction Figure 3 A timber-framed building during construction. system where all vertical and lateral loads are transferred to the foundations through a structural framework of small section timber studs sheathed with a wood-based sheet material such as orientated strand board (Figure 3). The framework is then