A separate design to calculate uplift should be carried out based on Irish Standard I.S.

If a roof has a pitch of less than 15 degrees and/or the site wind speed is greater than 26 m/s and/or the building is located in an exposed location (and there is reason to believe high wind speeds may occur), additional vertical restraint straps may be required. Twisted galvanised vertical restraint straps Trusses should not be notched to seat on wall plate. 105-1: 1977 Wire and cut nails for building purposes, staggered and fixed at either side of the truss, should be used to fix each truss to the wall plate such that no damage to the punched metal plate fixings occurs. In some cases, fixing using nails may be permissible.Īt least 2 wire-round nails more than 100 mm in length and 4.5 mm diameter, and in accordance with I.S. Usually, the instructions will include fixing the trusses to the wall plate using proprietary truss clips or strapping to both the wall plate and the masonry wall. The manufacturer’s instructions should be followed when erecting trussed rafters. The overhangs illustrated are acceptable if the manufacturer’s recommendations are followed when bracing the rafters and joists.ĭiagram D2(a) - Diagram illustrating overhang of a truss Approval from the truss manufacturer must be sought where special design is necessary. Unless the trusses are specifically designed, the truss must be supported directly on the ceiling chord immediately below the intersection of joist and rafter.

Rafter spacing for metal roof