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Treating Woodworm in Insulated Suspended Timber Floors

Question: We have a suspended timber ground floor above an accessible (around 4’6 foot high) cellar and I have insulated about half of it between the joists with fibrous insulation. What worries me (when the state of the world isn’t enough!) is that we have some live woodworm; every May we find a few beetles crawling about, and I fear I may have given them just the sort of environment they like, close, a bit damp, and undisturbed. Would I do better to remove the insulation and put bamboo strip flooring on top as we have had done in the hall? What do you think?

Answer: Woodworm in elderly suspended wooden floors is very common. You are fortunate in having accessibility to be able to deal with the problem easily. The course of action I would recommend would be to carefully take out your insulation and stack to reuse, brush the underside of the timber floorboards and the joists to remove debris such as spiders webs, and then to apply 2 coats of borate salt solution, such as Borotreat 10AQ,  either using a large paint brush or hand spray. Even though borates are a relatively ‘benign’ preservative it would be advisable to wear protective clothing and mask, and of course always read the instructions. This action will kill the beetle when it next exits the timber. For extra insurance you could apply the same solution to top of the floorboards.

Insulating suspended ground floors particularly where they are easy to access is one of the most cost effective measures one can do to cut your carbon footprint. I would suggest insulating the whole of your floor will make for a far more comfortable house. Laminated flooring on top of you existing floorboards has the added advantage of cutting draughts.

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