31 Aug 2023
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United Kingdom
Has anybody used or had experience with the specific brand, "Therma-Foil"?

I am considering using it as both some form of insulation and a vapor barrier. I have a suspended wooden floor, well ventilated below with air-bricks that are all clear. The company have assured me that I can lay 3mm hardboard onto my existing T&G floor and then lay the foil on top, then any laminate/carpet flooring can go on top of this.

I appreciate that this isn't going to give me as good an insulation value as 50mm-100mm of celotex between the joists, but under my circumstances this seems to me that it is an easy way of controlling draughts, vapour, noise and heat without lifting the entire floor nor crawling underneath shoving PIR between the joists.

Any experiences with this brand would be greatly appreciated.
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Is noise really a factor? or vapour? Vapour layers are important in highly insulative situations but this material isn't highly insulative so it isn't a significant factor here. Plus, most air loss will be around the perimeter and your underfloor is well ventilated so it really isn't a factor.

So the main benefit is reducing air loss (draughts) but that would be minimal through a laminate floor and, as vapour above, most will be around the perimeter anyway. If you really think it will be a problem, a poly sheet would be equally effective.

A decent quality laminate underlay would be just as good and will cost significantly less.
some form of insulation and a vapor barrier
Not thick enough to form an effective insulation layer but ok for vapour control if it's taped together with a suitably rated tape. Definitely no substitute for insulation in the other senses that you've used the word. Also, don't forget that joists are not great insulators, so insulating between joists does still leave significant thermal bridges to a cold area

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