Q I had a company out to give me a quote for treating some woodworm. They confirmed I have a small area (approx 1/2 of kitchen floor) affected. In the process they discovered I also have wet rot in some of my floor joists and they need to be replaced. The cause is leaking pipes under the bathroom & also the fact that some of the joists have been resting on wet masonry. I'm unsure if the masonry is simply wet because of the leak or if there is an additional cause. They have quoted me a substantial sum for replacing the joists with treated ones and replacing the floorboards. They didn't mention anything about needing to improve the subfloor ventilation so I'm not sure if this is an issue. I have another specialist firm coming out to quote but don't imagine they will be much cheaper. As I am about to start building work I ran the problem passed my builder who says he can replace the joists & sections of floor affected at a fraction of the cost (he's carried out this type of work before). I am also having a new bathroom & kitchen installed; the pipe work will be renewed & re-routed so this should solve the problem of the leak. My questions are
1. Do I have to improve sub floor ventilation? I have a semi bungalow (approx 1930s) that currently has 4 louvre style air bricks measuring 9" x 6", 2 at the front of the property & 2 at the rear. There aren't any on the side. I have a couple of stairs at the front so it's not possible to have 1 under the front door.
2. Will the builder have to use specially treated joists? If so what should they be?
3. Can wet rot develop into dry rot?
4. Once areas affected by woodworm & wet rot have been replaced,
a) Will any type of fungicidal treatment need to be applied?
b) Should entire subfloor level be sprayed with insecticide? (Bore holes only present at sub floor level)
A Thank you for your many questions. I answer below your questions in the order raised:
1. You can never have too much sub-floor ventilation. We would expect there to be more vents than two in the front and rear. We would expect there to be one every 1.5 metres of exterior walls if all floors inside are suspended timber floors. It sounds like, but we cannot be certain without seeing, that the wet rot was caused by timber in direct contact with damp sub floor masonry - not the lack of ventilation.
2. The builder does not have to use specially treated timber but industrially pre treated timber is the best and probably worth the small additional cost (labour will be the same)
3. Wet rot does not change into dry rot. They are totally different fungi with similar but different requirements.
4. a) It is not possible to apply by surface application an effective treatment that will prevent future fungal decay. Do not let yourself be talked into this. If you keep the timbers dry and well ventilated no wood rotting fungi can develop.
4. b) A sub floor area is open/interconnected and it is therefore possible that woodworm is present in other areas as well. Is it possible to crawl underneath to check? Only spray all floors if it is justified.
Hope the above is of assistance to you.