Technical Guidance Document A of the Building Regulations specifies that the requirement for strapping at ceiling level depends on the height of the apex and the thickness of the wall. Please note you must build the straps into blockwork as courses are being built. Straps to gable walls at rafter and ceiling level should be at centres less than 2m. Gable walls should be tied to roof timbers as illustrated in Diagram D4 below for stability. Please note: wall plate should have a width of at least 100 mm and a depth of at least 75 mm.ĭiagram D3 - Truss bearing strapping to walls Where wall plates are butt-joined, the trusses should be strapped (hold down straps) at no more than 400 mm centres on each side of the joint. Galvanised straps should be used to fix the wall plate to the masonry these straps should be at no more than 2 m centres or alternatively, the wall plate can be fixed using bolts at 1.2m centres. Trusses can be held down by fixing them directly to the wall plate using proprietary truss clips. Twisted galvanised vertical restraint straps are usually 30mm x 2.5 mm in cross section and should be included at the truss nearest the gable, and at 2 m maximum centres along the roof. EN : 2005 + A1: 2010 Eurocode 1 (Eurocode 1: Actions on structures - Part 1-4: General actions -Wind actions ). 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.
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