Timber frame buildings: a guide to the construction process

1 Timber frame is a modern method of construction (MMC) using standardised, prefabricated timberwall panels and floors commonly in use in manydeveloped countries which bears no relation toits Tudor post and beam namesake. Nor does itbear much relation to the form of softwoodframing common in the 19th and first half of the20th centuries. This modern method ofconstructing housing and other buildings usesadvanced breathable membranes, insulation andvapour control layers along with careful detailingto ensure durability. Building regulationrequirements for thermal, acoustic and fireperformance are all incorporated into the timberframe frame offers a number of advantagescompared with most other forms of construction . The package delivery of a completeweathertight structure consisting of inner leaf,internal partitions, floors and roof, within apredictable timetable, helps in meetingconstruction schedules Timber frame construction provides readyroutes for wiring and plumbing, significantlyreducing the time required for these operations The Timber frame acts as a template, withpredetermined openings.

2 This reduces settingout and results in dimensional and doors can be fitted easily construction processes can be undertakensimultaneously, with work, such as wall lining,starting much earlier in the build is taken off the critical pathTimber frame buildingsA guide to the construction processDigest 496 Timber frame is a well proven, versatile construction method with the following key benefits: offsite construction method fast erection reduction in overall build programme reduction in risk of delays ease of project planning reduction in site storage requirements reduction in site waste use of a sustainable building material achieves a high BREEAM or EcoHomes early involvement of the Timber frame specialist from project conception, an optimised design solution and build programme can be technical description of Timber frame construction is givenon pages 10 and Reynolds and Vahik EnjilyBRE Centre for Timber Technology and ConstructionFTimber frame housing under construction at Madley Park,WitneyThis Digest is not intended to provide guidance on all themany checks required for Timber frame , nor specifictechnical guidance on the structure and detailing.

3 Forguidance on site checks refer to the UK Timber FrameAssociation publication, A pocket guide to Timber frameconstruction(UKTFA, 2004). Timber frame can lead to reductions in sitestorage requirements and site waste It facilitates increased flexibility in theconstruction project as a whole. Through fasterbuild programmes, it can lead also to higherturnover Timber frame allows prefabricated floor unitsor cassettes to be installed. It also allows thepre-assembly of trussed rafter roofs on the safeworking platform of a lower floor Using floor cassettes ensures that all the joistsare set at the same level and correctly , offsite manufacture enhancesquality and speed of construction as well assafety on site Internal trades can continue, irrespective ofprogress on the external envelope, and in arelatively clean environment Less risk of delays through bad frame is one of the fastest methods ofconstruction.

4 It is quite common for a semi-detached unit to be completed from concretefoundation slab to weathertight stage, includingroof battens and felt, in only 4 or 5 days. Thistimespan can be shortened if required. Offsitefabrication processes allow the delivery to site ofstructural Timber panels for both external andinternal walls, and floors, on a just-in-time frame suppliers often include in thepackage the roof trusses, gable spandrel panelsand gable ladders; and may also supply and fit the windows, doors, staircases, insulation andcavity the early involvement of the Timber framedesign, fabrication and erection team, togetherwith appropriate project planning, the advantagesin productivity offered by this method can berealised (Figure 1).2 Case study 1 Main Contractor: Bellway HomesProject: Thames Gateway, Purfleet.

5 Mixed social and private housing comprising365 flats and housesBenefits experienced from Timber frame compared with traditionalmethods: shorter overall build time more flexibility in programming the build sequence finishing trades completed earlier less affected by poor weatherSpecial consideration was given to the following: using experienced erectors using good quality Timber ensuring accuracy of sole plate fixing and correct packing for levelsTypical construction time for a block of five terraced houses, from slab tocompleted roof structure, was 10 study 2 Main Contractor: Leadbitter ConstructionProject: Madley Park, Witney. Mixed private and housingassociation properties (see photograph on page 1)Phase 1: 41 units comprising two-bedroom and three-bedroom flats, town houses and bungalows. Half thesite was traditional build, half Timber frame .

6 Thetimber frame half was completed 10 weeks ahead ofthe schedule for the traditional build programme (total contract period was 56 weeks)Phase 2: 59 units, all in Timber frame . The first 34 unitswere completed 12 weeks ahead of scheduleBenefits experienced from Timber framecompared with traditional methods: consistent delivery ability to meet decreasing contract periods more project control construction process less affected by weather easier to plan following trades fewer construction problemsTypical construction programme for a two-storeyblock of three two-bedroom houses was to:Day 1: erect the ground floor including the first floor deckDay 2: erect the trussed rafter roof on the first floor deckDay 3: remove the roof and complete first floor wall panelsDay 4: place the roof; complete the fascias and soffitsDays 5 and 6:complete roof tilingThe procurement and construction processProject inceptionTimber frame can be considered for the followingmarkets: private housing, including flats social housing, including flats commercial buildings (eg hotels, offices,schools and hospitals).

7 In many cases residential developments are mixed,with a requirement for the inclusion of client s reasons for considering Timber frameinstead of a traditional method may be acombination of any of the following: responsibility for the design of the mainstructural element, apart from the foundations,is covered by the Timber frame specialist supervision of workmanship is theresponsibility of the Timber frame manufacturerreducing the workload of the main contractor a single point of purchase for the Timber framepackage, including the roof, helps to reduce themain contractor s estimating and purchasingworkload a versatile and capable building system sustainable construction a predictable build programme firm datesestablished for deliveries make site planningeasier, particularly on sites with difficult access speed of project turnaround a reduced risk of delays predictable costs health and safety compliance overcoming traditional skills shortages overall qualityThe priorities of these drivers depend on the typeof client and the nature of the project, and maychange with differing market conditions and forother reasons over the lifespan of the project.

8 Thepriorities may also be different for differing roleswithin the Timber frame industry provides a variety ofservices. Most firms produce floor and wall panelsto order, and may also provide full design,fabrication and erection services for the wholestructure including the roof. The Timber framespecialist has responsibility for the design of thestructural frame which is usually offered as a lumpsum fixed instructionPlanning approvalTender issueTender acceptanceConcept designInitial evaluationProject planningPreliminary designDetailed designFinal engineering evaluationDESIGN FREEZETARGETS METCostTimeQualitySafetyProject stagesTimber framesupplier sinvolvementClient benefits Meet building regulations Meet sustainability and environmental targets (eg BREEAM and EcoHomes ratings) Optimised solution Tailored specification Reduced design and detailing input Improved buildability Reduced waste Reduced costs Predictable costs Predictable build programme Just-in-time delivery More control Greater flexibility Increased completions Greater productivity Build programme met Less affected by weather Easier to plan following trades Clean working environment Health and safety Speed of buildFigure 1 Typical Timber frame procurement and construction processComponent manufactureDeliveryCompletionErectionIns pectionHandover Building ResearchEstablishment EnvironmentalAssessment Method.

9 Phases staged to suit build programmeInitial evaluation and concept designThe client should provide at an early stage thefollowing: building usage and loadings performance criteria for floors and walls cladding type roof type and covering eaves and verge details door and window details outline architectural drawings level of prefabrication required site details including any constraints on access,deliveries and lifting health and safety information proposed build programme and start dateEarly interaction between the client (or developer)and the Timber frame designer will facilitate aneconomical approach that provides an optimisedsolution, reducing material waste. Many timberframe clients have found that a partneringapproach, from project inception through tocompletion, has produced a specification tailoredto the construction method.

10 This can result inreduced construction costs, increased buildability,and minimises any potential design andspecification the concept design stage, Timber framemanufacturers can provide indicative prices andoutline build client, the Timber frame manufacturer anderector should agree on risk assessments andmethod planningKey milestones should be agreed in advance toallow the Timber frame manufacturer to plandesign and fabrication processes, deliveries andsite erection efficiently. The reduction indowntime for the manufacturer helps to minimisecosts to all parties, reduces uncertainty, and allowsthe build programme to be adhered plan an effective build programme, the timberframe manufacturer (who generally provides anerection service) will need to receive the fulldetailed design information in good time.