Sell the right treated timber

Sell the right treated timber

David Hopkins, CEO of Timber Development UK, explains why merchants need to double check that they’re selling correctly treated timber to their customers.

Not all timber is the same. Some species of timber are more durable, while others are less prone to shrinking or warping, and so are better placed for use in certain building work applications. Certain timber products are factory treated with preservatives to extend their useful life and make them safer to use in certain applications. These treatments can help to protect against wood-destroying organisms such as fungi or insects, and against damage caused by exposure to the elements.

It is essential that builders choose the right type of timber, especially when using it in an external, structural setting. Using the wrong treated timber can have serious consequences in terms of safety and durability.

Making the right choice is even more important when the builder is purchasing timber for a structural use, especially when it’s going to be fitted outdoors, perhaps as fencing, a joist, or part of a timber decking substructure.

The British Standard for wood preservation, BS8417, has created a number of Use Classes to help builders and merchants identify which treated timber should be chosen for specific uses. Three of the most common are Use Classes 2-4:

Use Class 2 – (Above the ground or DPC, covered): covers timber for interior use in a dry environment, such as battens, framing, joists, roofs
Use Class 3 – (Above the ground): covers timber for exterior applications above ground, such as deck boards, cladding, and fence rails. Use Class 3(u) indicates uncoated wood, while Use Class 3(c) indicates coated wood, such as on a painted timber window.
Use Class 4 – (In ground contact): covers wood used on, or in, the ground and for external structural support, such as fence posts, deck posts, joists and beams, whether or not it sits on other materials, like an under-deck weed-suppressing membrane.
To help merchants better understand which timber should be sold for which use, Timber Development UK members who supply preservative-treated softwoods have committed to clearly mark the relevant Use Class application on their sales and delivery notes, as well as their invoices. This commitment has been in place since 1 April 2021 as part of our Code of Conduct, so check your supplier’s documentation today and, if you can’t see evidence of the Use Class, contact them straight away.

You might also have seen timber labelled previously as being ‘green treated’, but this phrase does not include enough information to correctly identify where the product should be used. If the timber products in your yard do not have a Use Class, or are just labelled as ‘green treated’, contact the supplier and ask for written confirmation of the Use Class application, otherwise you risk the timber being used incorrectly.

Make sure your branch staff are aware of the Use Class system, so they can help make sure their customers always pick the most suitable timber for the job.

Timber Development UK and the Wood Protection Association have published Guidance Notes to help everyone in the supply chain understand the different treatment preservatives and why they matter. You can download them from

This article was originally published in the March issue of Builders’ Merchants’ News