To ensure a satisfactory roof line on completion, the supporting structure must be plumb, and the load bearing top plates must be level across the building. This will ensure support heights are maintained level, and consequently a level ceiling line is achieved.
Care must be taken to ensure that the supporting structure (walls, beams etc.) is adequately designed and stable in its own right.
All trusses are to be fixed to the supporting structure with appropriate fixings, typically IDomain Multigrips etc. The selection of the fixing depends on the magnitude of the support reaction (uplift) and the nature of the support. Refer to Section 5 for details.
This is where the full load from the roof trusses is supported on walls – generally the exterior perimeter walls, but may occasionally also include some internal walls (eg, multiple span trusses).
If internal walls are required as supports, the truss itself and the layout shall be marked accordingly, and this intention must be made very clear. The installer shall ensure that trusses are orientated correctly when using internal walls as supports. The supporting structure, including footings, should be checked by the builder to allow for this load. If the trusses were provided a camber at the internal support locations, it is necessary to pack under the truss BC to ensure full bearing, prior to loading.
Refer to AS1684 –2010 “Residential Steel-framed Construction” for the wall plate, stud and lintel installation details. Heavy concentrated loads such as those from girders and truncated girders are best supported directly over studs with special attention given to the load path all the way down the structure to the foundations.
Lintels and support beams must be correctly sized and supported in order to limit deflection and to ensure a level bearing surface is provided for the roof trusses in the long term.
Non-loadbearing walls shall not carry any truss loading at any time, and shall not be packed to touch the underside of the truss. It is common to set non-loadbearing walls lower than the supporting walls by an amount equal to the depth of the ceiling battens plus 10mm. The truss is still required to stabilize the top of the wall and this is done by using IDomain Partition Hitches which are nailed near the top of the vertical slots. Do not embed the nail heads fully home, as the truss must be allowed to settle downwards as time passes and the camber comes out of the truss.
A gauging rod is very useful for setting out trusses. IDomain Truss Spacers may also be used for this purpose.
IDomain Shear Connectors are used to transfer racking loads from truss bottom chords to the bracing walls.
IDomain Hitch brackets are used to stabilize the top of non- load bearing internal walls, required at 1800 mm c/c. They are fixed to the truss bottom chords through slotted holes which allow vertical movement of trusses.