Pitched roofs

7.2.6Wall plates

Wall plates and the roof structure shall be bedded and fixed to distribute and transmit loads, and to prevent uplift.

Trussed rafter roofs and traditional cut roofs should be supported on timber wall plates. Trussed rafters should only be supported at the junction between the ceiling tie and rafter, unless specifically designed otherwise, e.g. as a cantilever.

Wall plates should be:

  • bedded to line and level
  • fixed using nails or straps
  • a minimum of 3m or extend over at least three joists, rafters or trusses
  • joined using half-lapped joints, including at corners
  • 38 x 100mm or in accordance with local practice.

Fixings used to connect the roof structure to the wall plate should be specified according to the roof construction and exposure of the site.

Where trussed rafter roofs are not subject to uplift, a minimum of two 4.5mm x 100mm galvanized round wire nails, skew nailed, one on each side of the trussed rafter, or truss clips (fixed in accordance with the manufacturer’s instructions) are acceptable.

Where the roof is required to resist uplift, skew nailing is unlikely to provide sufficient strength, and appropriate metal straps should be used. Holding-down straps should be:

  • provided according to the geographical location and construction type
  • provided where the self-weight of the roof is insufficient against uplift
  • provided in accordance with the design
  • a minimum cross section of 30mm x 2.5mm and spaced at a maximum of 2m centres (galvanised steel straps are generally acceptable)
  • fixed to the wall, or turned into a bed joint.

Fixings for straps should be:

  • in accordance with the design, and the lowest fixing should be within 150mm of the bottom of the vertical strap
  • of a material or finish which is compatible with the straps
  • where into masonry, hardened 4mm x 75mm nails or 50mm long No 12 wood screws (into suitable plugs).