View
218
Download
3
Category
Preview:
Citation preview
CREATING ROOFSCAPES WITH TRUSSED RAFTERSTrussed Rafters have become part of the modern buildingvocabulary. Around 95% of all new house roofs are constructedusing trussed rafters as are an increasing proportion of roofs fornondomestic premises such as offices, retail outlets, hospitalextensions, leisure developments etc.
The trussed rafter form of construction is well known for itseconomy, off site prefabrication, speed of erection and theminimal environmental impact of its timber base. What is notalways so readily recognised is the flexibility and adaptability ofthe system and its ability to cope with a wide range of roofshapes such as hips, intersections, corners etc without the needfor any special forms of construction. The variation in roofingstyles possible with trussed rafters is unlimited.
Within this Product Data Sheet are a series of standard detailsof differing roof styles. These are the most commonlyconstructed roof shapes and the detailed solutions indicate away of achieving them. It must be stressed that these are notabsolute solutions but simply give an idea of how roofscapesmay be easily achieved.
It is hoped that by showing these few solutions users andspecifiers will see that many differing roof profiles may besolved using the same simple, readydesigned techniques.
However, it must be stressed that each specific case will haveits own individual characteristics and readers are stronglyrecommended to contact a TRA Member fabricator/designer asearly as possible in a project in order to discuss a detailedsolution.
Sheet No.6 May 2007P R O D U C T DATA S H E E T
Duopitch Hipped ‘L’ return
‘T’ intersection Dormer Dogleg Monopitch
Overlaid hip Gablet Dutch or Barn hip Mono ‘L’ return/hip
PA G E 2
Fig. 1 Flat top hip
Fig. 2 Typical ‘T’ intersection
Hip boards to be birdsmouthedover the compound girder of flattop trusses and over thewallplate
Compound girder of flat toptrusses permanently fixedtogether
Standard trusses to main roof
Flat top trusses supplied withextended rafters for site cuttingto suit hip boards
Noggings to be nailed to ceilingjoist and side of jack rafter
Monopitch trusses supplied wthextended rafters for site cuttingto suit hip boards
Infill jack rafters to be aminimum of 25mm deeper thantrussed rafter rafter members toallow for birdsmouthing atwallplate
Infill ceiling joists
Lateral bracing
Jack raftersshown in partonly for clarity
Set of multiple diminishingvalley frames nailed directly tothe main trussed rafters. (Theinternal members of the valleyframes are omitted for clarity)
Compound girder of ‘Howe’trusses permanently fixedtogether
Standard trusses with eavesoverhang removed on ‘T’ side
Standard trusses to main roof
If a loadbearing wall or beamis available to span betweenpositions A-A to support thestandard trusses of the mainroof, the ‘Howe’ girder can besubstituted by a standardtruss on the ‘T’ return roof
A
A
Fig. 3 Typical ‘L’ return
PA G E 3
Fig. 4 Overlaid hip
Ridgeboard
Set of multiple mono valleyframes (smallest omitted forclarity)
Compound girder of multipletrusses permanently fixedtogether
Compound girder of flat toptrusses permanently fixedtogether
Lateral bracing
Standard trusses with eavesoverhang removed on hip side
Set of multiple valleyframesincluding two special flattop frames to spread imposed load
Standard trussed rafters
Standard trusses to main roof
Compound girder of flat toptrusses permanently fixedtogether
Hip boards to be birdsmouthedover compound girder of flattop trusses and over wallplate
PA G E 4
T R U S S E D R A F T E R A S S O C I AT I O NP.O.Box 571Chesterfield S40 9DHTel & Fax: 01246 230036email:info@tra.org.uk
www.tra.org.uk
This product Data Sheet has been produced to give some ideas on how trussed rafter construction may be adapted in order to provide arange of roof intersections within the overall roof structure. However, it must be stressed that these are typical solutions and each roofwill have its own individual characteristics, readers are strongly recommended to contact a TRA Member fabricator/designer as early aspossible in a project in order to discuss a detailed solution.
More details on trussed rafter construction are contained within the TRA ‘Technical Hanbook’ which is a priced publication available fromthe Trussed Rafter Association at the address given below.
The guidelines within this Data Sheet are issued in good faith but without liability and its use is entirely at the user’s risk.
Fig. 5 Dogleg intersection
RidgeboardRidgeboard supportledgers nailed tocompound girdertrusses
Standard trussesto main roof
Binders
Infill ceilingjoists
Compound girder trusses permanently fixedtogether
Infill rafters to be25mm deeper thantrussed raftermember to allow forbirdsmouthing atpurlin and wallplate
Standard trussedrafters to main roof
Compoundgirder truss
Purlin
Purlin support securely nailed tointernal truss member. Minimumsize to be 60mm x width ofcompound truss
The five roofscapes illustrated on this Product Data Sheet are those most commonly constructed.There are many other ways of framing hips, corners, and intersections etc with trussed rafters.Please contact your TRA trussed rafter fabricator for details. Throughout this document requiredwind and stability bracing has been omitted for clarity
Common raftersomitted forclarity
Recommended