How does treated timber affect indoor air quality?
With mounting concerns over the quality of the air we breathe, a recent study examined the impact of timber treatments. Gordon Ewbank explains.
We now spend 90% of our time indoors and it’s widely accepted that the indoor environ-ment in our homes, schools and workplaces can have a significant impact on our health. And while recent governments have concentrated on making improvements to outside air quality through reduced vehicle emissions, until recently the focus on indoor air quality has lagged behind.
However, the issue of indoor air quality and its impact on health and wellbeing is now gathering momentum. In particular, questions are being asked about the effects of products used for construction, including timber.
The Wood Protection Association commissioned the BRE to look at preservative pre-treated wood used in construction. The study examined all the available scientific evidence, to help understand how treated timber performs in the context of air quality within buildings.
Preserved timber is present in a large range of construction products in our homes, including parts of the structural timber frame, roof trusses, window frames and tiling battens. These products do not usually extend into the living space but are integral to the building structure.
The tests found that emissions from treated timber were minor, due to the low volatility of the active substances in the treated wood. Moreover, as preserved timber products are not usually used within our living spaces, any emissions would need to pass through insulation, lining boards, plasterboards, paints or decorative coatings before they reach the indoor air.
The study concluded that preservative pre-treated wood poses no threat to indoor air quality, stating that: “The available scientific evidence suggests that emissions from preservative treated wood particles to air are small and, further to that, the complexity of the pathway from air within the building envelope/cavity to the indoor air compartment means that the concentration reaching indoor air is negligible. Thus, the evidence indicates preservative-treated wood poses no threat to indoor air quality.”
Timber remains one of the most sustainable building materials available and the safe and appropriate use of preservatives can help to enhance its performance for specific applications. Preservative pre-treatment extends the service life of wood for many years. At the end of the its life, treated wood can often be reused or recycled.
Gordon Ewbank is chief executive of the Wood Protection Association
Key points to consider when specifying treated timber
First, always ask the question, does the wood need preservative treatment? This will depend on what the timber will be used for, the potential risks and consequences of premature failure and the natural durability of the chosen wood.
Don’t assume all treated wood is the same. Make sure you choose the appropriate treatment for the end use of the timber by selecting the appropriate use class. For example, different treatments are appropriate for fencing or decking, joinery or structural applications.
An outdoor deck or fence post in contact with the ground will require higher levels of preservative than an internal floor joist for long-term protection. More details at: www.wood-protection.org/preservation/british-standards-use-classes.
The British Standard for wood preservation is BS 8417. This code of practice defines treatment by preservative and retention requirements by:
- The use class.
- The species of wood.
- The component description, for example fence post, cladding.
- The desired service life: 15, 30, 60 years.
The Wood Protection Association provides guidance on specification of all wood protection systems.