Source: Timber Trade Federation
Understanding use classes & applications.
Do your staff know each timber’s Use Classes?
Preservative treatments for all timbers, including garden products, fall into various use classes depending on their application. Make sure your staff are trained to use the material with the correct level of treatment for the customer’s end use.
Use Class 4 treated timbers as an example include decking joists and posts, and timbers in ground contact such as fence posts and agricultural timbers. Use Class 3(u) treated timbers are for use above ground in fully-exterior situations, for example deck boards that are not in contact with the ground, claddings and fascias. Use Class 2 timber treatments are for timbers used in covered situations. Examples are tiling/roofing battens (slatings), framing timbers, internal joists and roof timbers.
Treatment colours & cut ends
The Use Class is the key to using a fit for purpose product. The colouring of a timber treatment, for example ‘green’ or ‘brown’, does not define performance. Advise your customers that cut ends of treated timber need to be resealed using an end grain coating to maintain the integrity of the treatment long term. Such coatings are also an opportunity for extending services to clients.
Rule change: Substructures
The British Standard covering decking joists and substructures is changing during 2020. In future, all decking substructure material needs to be treated to Use Class 4 for use in ground contact.
Suppliers will need to segregate stocks of deck joists away from stacks of standard carcassing, which can often have the same dimensions. Standard carcassing is only treated to Use Class 2 for interior use so will fail if used outside. Check with your supplier that you’re using material with the correct Use Class treatment, and make sure all your staff are aware of the changes.
New technology in treatments
For fence posts intended for Use Class 4 treatment, incising allows greater penetration of the preservative treatment into the wood. The timber is kiln-dried carefully to a particular moisture content, then multiple fine saw cuts at varying angles are made into the posts. This combination allows the maximum take-up of the treatment.