Between floors insulation queries

13 Aug 2015
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United Kingdom
After some advice regarding insulation between floors in a full refurb of our recently purchased house.

Under the floors upstairs would it be suitable to lay 100mm of rockwool between joists? Or is it recommended to use an insulation with acoustic properties too?

Downstairs is a mixture of solid and suspended floors. There is good ventilation under the suspended floors, is it recommended to have any sort of insulation under the floorboards to stop drafts etc coming up?

We also have a single story kitchen extension with a pitched roof. Everything is stripped currently, with only a newly screeded floor in place and ceiling joists exposed. I would obviously like to insulate the ceiling to stop the heat going in to the ceiling void, but I also want to board out some of the area too. Would 100mm rockwool between joists with chipboard flooring above be sufficient?

Thanks in advance.
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Rockwool has pretty good sound proofing properties, so would be the best solution, but I can't remember if I used 100, or 170 when I did the same sort of job. You'll want 100mm celotex in the kitchen roof space, but if the floors just been screeded, what's being boarded.
Ok thanks.

I mean some of the floor space in the kitchen ceiling void will be boarded to provide some storage. Just wondering if 100mm of rock wool between joists will be sufficient for heat retention in the kitchen? Wanted to avoid 100mm celotex if possible due to cost, but if it will be far superior then I will be prepared to pay out for it
You're trying to insulate the storage area, but with 100mm of rockwool, you'll stil be losing het up there, so you maybe need to think about treating it in the same way as the roof itself. Search for insulation seconds on eBay, and you can pick up some bargains. Rockwool is good for laying down, but not so good for pushing up into a void, as it tends to try and fall down, and you really want about double the rockwool as you do for celotex, but I'd go for 80 to 100 of celotex or equivalent. How much of the ceiling will be boarded.
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First off why do you want to insulate between floors? If for sound then use a rockwool sound insulation product such as RWA45. Incidentally that will give heat insulation as well. But unless this is between a garage and house say you don't want to heat insulation. Why would you want to heat insulated say lounge to bedrooms? The air will still move from heated part of the house to unheated and then unheated will get damp. Typically a house has 40-60% RH at 20C which is 100% RH at ~13C.

Also, building regs will say you kitchen ceiling should have 270mm of insulation (normally 100mm between joists and 170mm laid at 90 to joists) but if it is not a new extension then anything is better than nothing. You can get loft legs to raise boards above the insulation.

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