7.2 Pitched roofs

7.2.7 Joints and connections

Joints and connections shall be designed to ensure structural stability without undue movement or distortion.

Members should:

  • be accurately cut to fit tightly
  • not be damaged or split.

The following joints should be used at the main connections of traditional cut roof members:

Rafters to ceiling joists using a nailed lapped joint

The rafter should be birdsmouthed and skew nailed to the wall plate.

Rafter to purlin

A birdsmouth joint should be used, generally the purlin is fixed vertically.

Purlin connections

Support should be provided directly under the joint or a scarf joint used. Scarf joints should be made near to a strut so that the joint supports the longer span.

Scarf joint

Used to support the long span of the purlin.

Hipped roof joints

Angle ties should be used at the corners of hipped roofs to prevent the wall plates from spreading.

Where hip rafters are heavily loaded, eg carrying purlins, they should be jointed using dragon ties, or similar, to prevent the hip rafter spreading.

Diminishing truss support

Diminishing trusses should be adequately supported by one of the following:

  • by having a splayed bottom chord to ensure correct seating on the rafter or
  • by sitting on a continuous binder which is splayed to receive the diminishing truss (Figure 13) or
  • by sitting on 25mm x 38mm x 300mm long battens which are splayed to receive the diminishing truss (Figure 14) or
  • proprietary diminishing support brackets assessed in accordance with Technical Requirement R3.

Last updated: 2nd January 2024

Back to top ⇧