Are there any timbers have an inherent spread of flame classification?
Is it possible to treat timbers for class 1/class 0?
Spread of flame and fire resistance have to be treated completely seperately as they are two different performance characteristics.
As far as "spread of flame" is concerned, fire doors must prove fire resistance rather than spread of flame performance.
In the Approved Document B, the performance rating for untreated timber or plywood with a density of more than 400kg/m3 is class 3, it is therfore essential any untreated timber will need test evidence to prove that it has a higher rating.
As a rule, timber requires treating to achieve the higher ratings, consideration should be given to a timber treatment specialist being consulted to guarantee the appropriate choice of method.