Services in TimberFramed Construction

Guidance for a defect-free interface

Compiled by Jeremy Vibert, Barbara Keyworth andRoderic Bunn

InterfaceEngineering

Publications is aCo-Construct

initiativesupported by

What is Co-Construct?Co-Construct is a network of five leading construction research and informationorganisations - Concrete Society, BSRIA, CIRIA, TRADA and SCI - who areworking together to produce a single point of communication for constructionprofessionals.

BSRIA covers all aspects of mechanical and electrical services in buildings,including heating, air conditioning, and ventilation. Its services to industry includeinformation, collaborative research, consultancy, testing and certification. It also hasa worldwide market research and intelligence group, and offers hire calibration andsale of instruments to the industry.

The Construction Industry Research and Information Association (CIRIA )works with the construction industry to develop and implement best practice,leading to better performance. CIRIA's independence and wide membership basemakes it uniquely placed to bring together all parties with an interest in improvingperformance.

The Concrete Society is renowned for providing impartial information andtechnical reports on concrete specification and best practice. The Society operatesan independent advisory service and offers networking through its regions andclubs.

The Steel Construction Institute (SCI) is an independent, international, member-based organisation with a mission to develop and promote the effective use of steelin construction. SCI promotes best practice through a wide range of trainingcourses, publications, and a members advisory service. It also provides internet-based information resources.

TRADA Technology provides timber information, research and consultancy forthe construction industry. The fully confidential range of expert services extendsfrom strategic planning and market analysis through to product development,technical advice, training and publications.

For links to all Co-Construct members go to www.construction.co.uk.

Services in Timber Framed ConstructionCopyright of all material is this publication rests with TRADA Technology andBSRIA. Guidance appearing in the orange text boxes is copyright TRADATechnology, while all guidance in blue text boxes is copyright BSRIA.

Photographs and illustrations in this publication were provided by BSRIA andTRADA Technology unless otherwise credited.

Cover Illustration: A timber-frame house, courtesy ScandiaHus.

This publication was part-funded by the Department of Trade and Industry underthe Partners In Innovation (PII) collaborative research programme. The viewsexpressed in this publication are not necessarily those of the DTI. Final editorialcontrol and publishing responsibility of this publication rested with BSRIA.

©BSRIA/TRADA IEP6/2005 January 2006 ISBN 0 86022 650 6 Printed by Multiplex Medway Ltd

All rights reserved. No part of this publication may be reproduced, stored in aretrieval system, or transmitted in any form or by any means electronic or mechanicalincluding photocopying, recording or otherwise without prior written permission ofthe publisher.

1SERVICES IN TIMBER FRAMED CONSTRUCTION

Timber frame provides all the advantages of modern methods ofconstruction: project cost savings, quality build and reduced reliance onsite labour. In the UK, most timber frame is prefabricated off-site, whichoffers factory-quality accuracy and efficient use of materials.

To exploit these benefits detailed pre-planning and co-ordination isrequired between members of the design team. It is also vital to integrateservices concepts into the design at an early stage.

Timber framed construction was primarily developed in the UK forhouse building, although it is also widely used for buildings such ashotels, clinics, nursing homes, student accommodation, and offices.Following changes to the fire safety regulations in England and Wales in1991, multi-storey timber-frame buildings of seven and eight storeys arenow possible.

Compared with many large industrial buildings, most timber framestructures are not highly serviced. However, this does not mean thatservices are unimportant. They are fundamental to the comfort ofoccupants, have a significant effect on construction and running costs, anddirectly influence a building’s CO2 emissions.

The timber frame designer and manufacturer need detailed informationon the proposed services, such as space and weight requirements,dimensions, and proposed routes, so that these can be taken into accountin the panel layout. Equally, the services designer needs to understand theconstraints inherent both in the materials used and in the buildingsystem.

Everyone involved in the construction and the fit-out of a timber framedbuilding should have some understanding of the structure, the way that itis put together and how it works.The sequencing of operations on siteshould not be assumed to be the same as other forms of construction.

This publication is intended to encourage best practice for the installationof services in timber framed buildings. That said, there is more than oneapproach to providing buildings that will perform well in service, andmore than one solution to meeting the needs of the Building Regulations.Hence the details included here may differ from those used by individualcompanies in the industry and which may be equally acceptable.

Barbara Keyworth, TRADA TechnologyRoderic Bunn, BSRIA

December 2005

Introduction

2 SERVICES IN TIMBER FRAMED CONSTRUCTION

Introduction 1

The clients’ guide to timber framed construction 4Key issues 4

External walls 4Internal walls 4Party walls and floors 4Ground and intermediate floors 5Thermal, fire and acoustic performance 6Differential movement 6Services zones 7

Notching and drillingSolid timber joists 8Engineered timber joists 8Stud frames 8Roof members 8

Fixing to timber-framed walls 8

The clients’ guide to mechanical building services 10An introduction to building services 10

Plant space allowance and co-ordination 10Plant allowances 11Zoning 12Fabric airtightness issues 12Thermal comfort 14Radiator heating 14Underfloor heating 14Ventilation 16Windows and ventilators 16

Window installation in timber frame 17

Contents

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3SERVICES IN TIMBER FRAMED CONSTRUCTION

Further reading to support this guide

Standards for structural and services design

Glossary for definitions of terms

Advice about the characteristics of timber structuresis given by TRADA Technology in orange-tinted textboxes.

Advice about the interface issues of mechanical andelectrical services with timber structures is given byBSRIA in blue-tinted text boxes.

Comments marked by � link to the timber framesections listed under see also.

Comments marked by � link to the servicesengineering sections listed under see also.

Comments marked by denote a link common toboth services engineers and timber frame specialists.

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Links to services sectionsLinks to structural sectionsLinks to common sections

� Essential services engineeringmessages from the guide

� Essential timber frame messagesfrom the guide

See also

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The clients’ guide to electrical building services 18 Electrical systems 18

Earthing 18Bonding 18Metering 20Wiring 20Wiring in party walls and floors 20Installing sockets and switches 21Installing downlights 21

Issues to address when installing building services 22Drainage and plumbing 22

Soil and vent pipes 22Water storage tanks 22Water service pipework 22Party walls and floors 23

Gas installations 24Gas meter boxes 24Gas installation pipework 24Gas appliance installation 25Balanced-flue boilers 26Open flues 26Chimney breasts and stacks 26

Metal chimneys 28Clearances 28

Further reading and standards 30

Glossary of terms 31

Key timber-frame watchpoints

Key services watchpointsHow to use this guide

4 SERVICES IN TIMBER FRAMED CONSTRUCTION

1

Prefabricated timber-framed construction uses timber studs and rails, together with a wood-based sheathing, to form a structural frame which transmits all vertical and horizontal loads tothe foundations. Although the exterior cladding is non-loadbearing, it may contribute to wind resistanceand will weatherproof the building while providing the desired external appearance. Cladding can besupported on foundations or fixed to the timber frame.

Timber framed constructionThe clients’ guide to

Platform-frame is most commonly used in theUK. Each storey is framed with floor-to-ceilingheight panels with the floor deck used as theerection platform of the next storey (Figure 1).

Most UK timber frame wall panels arefactory prefabricated and delivered to site as akit.They vary from open panels of studs andsheathing to complete units includinginsulation, wall linings, membranes, andpossibly also windows and services. Floorsmay be prefabricated or built on site. Roofsnormally employ trussed rafters or sometimesprefabricated panels.

External wallsExternal wall panels are constructed fromvertical studs, normally 89 x 38 mm or 140 x38 mm, at 400 or 600 mm centres, nailed withsimple butt-joints to top and bottom rails. Thesize of the studs may be governed more by thethickness of insulation, than by structuralneeds.

Key issues

In multi-storey construction, multiple studsare used at lower storeys to carry the loads tothe foundations. Wind bracing is usuallyprovided by a wood-based board sheathing,typically oriented strand board (OSB), nailedto the external face of the frame (Figure 2).Other wall designs have been developed thatuse wood-based boards or fibre-reinforcedgypsum boards. These are fixed on the internalface of the studs to provide the wind bracing.

Internal wallsInternal walls may be built using a stud framelined on both sides with plasterboard or othersheet material. Internal walls that provide windbracing may be sheathed with a wood-basedboard.

Party walls and floorsCompartment or separating walls (also partywalls) are usually constructed from two separatestud frames with mineral wool insulation.

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See also

Timber Frame Construction reference,page 30 See further reading, page 30

Further reading on page 30

Standards on page 30

Glossary on page 31

Timber-frame panel structuresrely on both vertical andhorizontal framework forstructural performance

Membranes and linings play a vitalrole in the fire, acoustic andthermal performance of thestructure

Key timber frame watchpoints

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Room linings comprise at least two layers ofgypsum-based board applied with staggeredjoints to achieve fire and acoustic performance.

Compartment or separating floors (partyfloors) are constructed using solid timber orengineered timber joists using variouscombinations of other proprietary elements toachieve the required fire and acousticperformance. Details for these issues areincluded in the Building Regulations and relateddocuments.

Ground and intermediate floorsSuspended timber, suspended concrete andground-supported concrete ground floors areall used for floors. In timber frame, theintermediate floor generally acts as adiaphragm to transmit wind loads to the wallstructure. In platform frame, the floor zoneextends to the external wall cavity.

Although solid timber joists are typicallyused in low rise housing, prefabricated timberengineered I-joists or metal web joists areincreasingly being specified in medium risedevelopments.

Figure 1: The various elements ofplatform-frame construction. ©TRADA.

Figure 2: An external wall of a timber frame structure, showingsheathing on the outer face of the frame. Alternative wall designscan be found in TRADA’s Timber Frame Construction Book.

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Ventilated cavity

Internal lining Vapour control layer

Insulation

Timber stud

Sheathing to studframework

Breather membrane

Cladding

Services engineering issues

Timber frame issues