The shoe consists of a flat galvanised steel plate which is fixed to the underside of the rafter seating where it bears on the wall plate. To overcome at least the horizontal thrust from the roof structure and its imposed loads, a sliding truss clip or 'glide shoe' can be used. We are now back in effect to a collar roof (see Fig. The extended rafters then act as a beam which deflects to give an element of lateral movement. Unlike the conventional truss which is fully triangulated by virtue of its bottom chord fixing the top chords together, the raised tie roof completes its triangulation at the flat ceiling to sloping ceiling intersection. The raised tie roof truss imposes a horizontal load onto the wall plate and wall when loaded. a greater raise to the tie than is generally practical with methods 1 and 2, above. This particular detail allows a greater length of sloping rafter, i.e. 7.13), this time taken from Wolf's technical manual. (3) Use the plated chord discussed in 'Innovation', above (see Fig. This at least leaves the truss itself using relatively lightweight timbers, but it does mean that the bird's mouth becomes a difficult joint to cut on site. additional pieces of timber) nailed or bolted to each side of the rafter from the wallplate to the first node joint. If, however, it necessitates the use of 47 mm timber then clearly all the truss members must now be 47 mm, and there is a significant cost implication brought about purely by the need to overcome a structural problem occurring in the sloping ceiling area of the truss. (1) Increase the cross section of the top chord over the whole of the top chord length if this can be done by using 36 mm stock sections then there is no major cost implication. All plate producers have three alternative solutions: The extended rafter sections clearly carry the whole of one side of the truss, necessitating a larger section of timber for the sloping ceiling length.
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