Pitched roofs

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Adequate restraint shall be provided to support the structure, distribute roof loads and prevent wind uplift. Strapping shall be of adequate strength and durability, and fixed using appropriate fixings.

Restraint straps, or a restraining form of gable ladder, should be used where required to provide stability to walls, and be installed in accordance with the design.

Lateral restraint straps should be located:

  • for homes up to and including three storeys (two storeys in Scotland), at a maximum spacing of 2m
  • for homes four storeys or over, fixed at a maximum spacing of 1.25m.

Lateral restraint straps should be fixed to the roof structure by either:

  • fixing to solid noggings using a minimum of four 50mm x 4mm steel screws or four 75mm x 4mm (8SWG) round nails, with one fixing in the third rafter (Figure 1), or
  • fixing to longitudinal bracing members using eight 25mm x 4mm steel screws evenly distributed along the length of the strap (Figure 2). Alternatively, 100mm x 25mm timber members, fixed over four trusses and nailed in accordance with Clause 7.2.9 can be used where the position of the strap does not coincide with a longitudinal binder.

Lateral restraint straps should be:

  • ordered and supplied according to the design, i.e. the correct length and number of bends and twists
  • provided at rafter level on gable walls, where the home is of masonry construction (larger or separating walls may require restraint at ceiling level)
  • protected against corrosion in accordance with BS EN 845-1 Clause 6.1.11 Table 4 (sherardised straps or fixings are not acceptable in Northern Ireland and the Isle of Man)
  • of sufficient length to be fixed to a minimum of three trusses
  • a minimum size of 30mm x 5mm and have a minimum anchorage downturn to 100mm (or proprietary straps)
  • fixed with the downturn on a substantial piece of blockwork, preferably fitted over the centre of an uncut block
  • in accordance with BS EN 1995-1-1, where the home is of timber frame construction.

In framed roofs, as an alternative, purlins and pole plates can be used to provide restraint where the timber abuts a gable construction. Where purlins are used to provide restraint, the maximum permissible spacing is 2m unless the design shows otherwise.

Gable ladders can be used to provide restraint to the external wall where:

  • there is blocking between the last trussed rafter and the inner leaf (maximum 2m spacing)
  • the soffit board is cut carefully and then fixed securely to restrain the outer leaf.

Proprietary straps should be:

  • In accordance with Technical Requirement R3
  • Installed in accordance with manufacturer's recommendations.