Valley construction follows the design set out in Fig. 3.10, a principal truss being located on the ridge line of the intersecting roof in place of the double rafter illustrated. With equal span and pitch intersecting roofs, purlin lines will coincide and they can be fixed together with a steel connector as indicated in Fig. 3.11. Unequal spans will mean a hanger from the higher to lower purlins and/or additional support
again as indicated in Fig. 3.11. Support may also be required for the main roof principal truss if there is no wall on the normal plate line. It is not generally possible to support this principal from the first principal truss of the intersecting roof unless it has been specifically designed to carry the additional load. It is more likely that a steel or timber beam must be employed within the roof space, using a special steel shoe designed to carry the end of the principal truss. Figure 5.6 illustrates this junction. A beam beneath the truss is a more easily constructed detail, but its depth may restrict headroom below.
Care must be taken with this steel shoe design and the positioning of the supporting beam, to allow adequate 'end-distance' for the rafter to ceiling joist connector discussed earlier. Also the positioning of the truss to shoe locating bolt should ideally be identical to the bolts used to assemble that particular joint. Assembly on site would then require temporary removal of one of the joint retaining bolts whilst the truss is temporarily supported. A slightly longer bolt is passed through the steel shoe and the truss to complete the joint.
Lighter weight steel standard hangers can be used to support rafter and ceiling joist, although the location of the supporting beam may be such that an extended length of support in the shoe similar to that used for trussed hangers may be required to give adequate bearing to the supported structure members.
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