Typical timber roof member dimensions
50 mm
Standard timber roof member sizes, such as minimum 100x50mm for struts, 32mm thick for valley rafters, and rafter cut plus 25mm for ridges and hips, are generally acceptable
Standard timber roof member sizes, such as minimum 100x50mm for struts, 32mm thick for valley rafters, and rafter cut plus 25mm for ridges and hips, are generally acceptable. For non-standard configurations or critical structures, an engineer must design timber sizes in accordance with structural requirements.
Basis in regulation
BS 5268
Read the source
How to check it on site
Measure key timber members to confirm they meet minimum specified sizes, or match engineer's drawings.
Common failure
Use of undersized timber members, particularly for critical elements like valley rafters, without engineering justification.
Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.