Do any timbers have an inherent spread of flame classification? And how do I treat timbers for class 1/class 0?
Spread of flame and fire resistance are two quite separate performance characteristics. Fire doors must prove their fire resistance rather than spread of flame performance.
In Approved Document B, the typical performance rating for untreated timber or plywood with a density of more than 400kg/m³ is class 3 and therefore any untreated timber will need test evidence to prove that it has a higher rating.
In general, timber will need treatments to achieve the higher ratings. It is recommended that a timber treatment specialist is consulted to ensure that the most appropriate method is chosen.
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