Technical Guidance

Question:

Do mono-pitch trussed rafters, bearing in the web of a steel joist, need to have solid blocking like floor joists, or is the longitudinal bracing, nailed on top of the ceiling joists sufficient?

Considerations:

• Diagonal bracing is provided to triangulate the roof structure and provide resistance to the lateral forces acting on the roof members.

• The Trussed Rafter Association technical handbook says that the diagonal bracing should be fixed to the wall plate.

• BS 5268 : Part 3 ‘Code of practice for trussed rafter roofs’ refers to the bracing being fixed to the wall plate.

• BRE good building guide No. 8 describes methods of fixing the bracing to the wall plate.

• NHBC Standards clause 7.2 - D5(c) says diagonal bracing should be fixed to wall plate.

Answer:

The diagonal bracing should be fixed to the wall plate.

• Where possible the bracing may extend over the wall plate and be fixed with two nails, or

• If the bracing cannot extend over the wall plate it can be cut on a splay and fixed to the top of the wall plate with a 30 x 5mm bent galvanised steel strap, twice nailed to each member.