Roof timber durability for condensation risk
What it looks like
Failure to account for increased condensation risk under certain roof coverings, leading to the use of insufficiently durable timber and subsequent decay.
Why it happens
Within pitched roofs, particularly where continuous, impermeable coverings or membranes are used, the risk of condensation forming on timber components is elevated. To mitigate potential degradation, all structural timber elements in such conditions must be specified with enhanced durability, either through preservative treatment or by utilising naturally durable heartwood.
What it costs if it is missed
Within pitched roofs, particularly where continuous, impermeable coverings or membranes are used, the risk of condensation forming on timber components is elevated. To mitigate potential degradation, all structural timber elements in such conditions must be specified with enhanced durability, either through preservative treatment or by utilising naturally durable heartwood.
How to inspect for it
Confirm that all timber rafters, purlins, and other structural elements under impermeable roof coverings are either treated or of a naturally durable species.
How to prevent it
Within pitched roofs, particularly where continuous, impermeable coverings or membranes are used, the risk of condensation forming on timber components is elevated. To mitigate potential degradation, all structural timber elements in such conditions must be specified with enhanced durability, either through preservative treatment or by utilising naturally durable heartwood.
Basis in regulation
BS EN 350
Read the source
Last updated 23 August 2026. This is our editorial summary of publicly available regulation and site practice, not building control approval or a warranty determination.