10 TOP TIPS FOR BUYING PRESERVATIVE TREATED WOOD
Assume all treated wood is the same and you could be making a big mistake. Whilst one piece of treated wood may look very much like another the level of preservative protection could be very different. That’s because the British Standard for wood preservation (BS8417) requires that the level of preservative impregnated into the wood reflect the components end use and service life. An outdoor deck or fence post in ground contact for example will contain higher levels of preservative than an internal floor joist. The level of treatment reflects the risk of wetting and the onset of decay in service. Use a joist treated for an indoor application for say a garden deck joist and premature failure is almost inevitable.
BS8417 groups wood used in construction and landscaping into four ‘Use Classes.’ Use Class 1 is for internal applications where there is infrequent risk of wetting. Use Class 2 for internal applications such as roof timbers where the wood may be exposed to wetting, condensation or damp over its service life. Use Class 3 relates to wood exposed to the weather but not in direct soil or fresh water contact whilstUse Class 4 applications deal with the treatment of wood used in permanent contact with the ground or fresh water.
BS8417 further tailors the level of preservative treatment of a component by service life. The Standard provides for three desired service life periods of time - 15 years, 30 years and 60 years. Treated wood performs fantastically when it is treated correctly for the end use and desired service life. Always make sure treated wood is fit for purpose by following the WPA’s top tips:
10 TOP TIPS FOR BUYING & USING PRESERVATIVE TREATED WOOD
1. Always identify the application Use Class before ordering;
2. Tell your supplier, in writing on a purchase order preferably, that the wood must be impregnated in accordance with BS8417 for this Use
3. Specify the desired service life period you require: 15, 30 or 60 years. For external applications like fencing and decking 15 years is the
default standard. Longer desired service life components e.g. 30 years fence posts are usually treated to order so build this lead time into
your project plans.
4. Incising (symmetrical piercing of the surface of sawn timber ) is used to assist preservative penetration. Expect to see it on square sawn
posts treated for the higher 30-year specification in BS8417 (Round posts don't need incising to meet the 30-year spec.)
5. Ask your supplier to confirm on the delivery note/ invoice or provide a separate treatment certificate that the wood supplied meets your
6. When buying treated wood from stock always get the supplier to verify, in writing, which Use Class and desired service life standard it is
7. Never substitute wood treated for an indoor Use Class for an external Use Class – failure is inevitable.
8. For wood in permanent ground or freshwater contact Use Class 4 levels of protection must be achieved. Anything less and service life,
structural safety and customer satisfaction will be compromised.
9. Always buy a can of end grain preservative for sealing untreated wood exposed when cross cutting, notching or boring treated products
10. When third-party reassurance of fitness for purpose is required ask for components certificated under the WPA Benchmark quality
assurance scheme. Find sources here: https://www.wood-protection.org/quality-assurance/
IF IN DOUBT CONTACT THE WPA HELPLINE FOR FREE GUIDANCE
CALL 01977 558274 OR E-MAIL: firstname.lastname@example.org