Hi,
I live in a 1930s semi which has a void underneath the living room that is about 6 foot deep. Although the wooden floor is carpeted, would it help to insulate underneath the floor with something like celotex between the joists? If so, do I need to leave a gap between it and the floor and/or put any membrane layer somewhere? The void has a concrete floor that has always been bone dry.
Grateful for any advice as to me the living room does not seem to heat up to well.
TIA
Yes, definitely.
If so, do I need to leave a gap between
The void should be ventilated to teh outside world. it is advisable to put a vapour barrier between the joists and the flooring above the insulation.
What I would do is to lift the floor, nail battens to the joists to support the insulation, at the right height to bring the celotex panels flush with the joist tops, and then tape over the joists and panels with celortex foil tape.
The floor is less relevant than walls, typically, but easier to sort out.
Do you mean that the vapour barrier should run underneath the floor over the joists and insulation? i.e. directly beneath the floorboards?
And lay the barrier over that before putting the floorboards back down?
I should have mentioned I can access the void and could work from below without lifting the floorboards.
TIA
yes.
Ah. In which case take a chance, and simply slap the insulation up and between with a dab of no more nails?
And use some mastic to _utterly_ seal any gaps. Its not as good as overall vapour barrier, but should be good enough.
(snip)
Many thanks for the info. Wil try and get round to it as soon as the weather warms up a bit :-))
Best regards.
With a six foot void, make an access and work from below is probably easier.
In article , ZeitGeist writes
Celotex is the easy option but you could do it for a lot less with rockwool, you have plenty of working space and will have plenty of joist depth to take the less effective insulation. You can support Celotex with slant driven 4" nails or rockwool with hardboard and battens.
I have done this with fibreglass and didn't bother with the vapour barrier.
I think polystyrene is ok for ground floor
Dear ZG I disagree with the other posters for the following reason: the vapour check needs to be on the warm side of the insulation and all timber needs to be inside that or you will find a potential condensation trap made What to do? Slap 2" (or more up to 4") of TP 10 or the like (PU foam with foil) UNDER the floor to the joists with long stainless fixings (the pink ones used for outside insulation adapted to suit) or screws and large 2" plate washers in plastic Fill any gaps well but preferably dont have any - good interference fits - If gaps inevitable at say edges use foam gun above and below
That should do it
Make sure void is well vented to ouside
If you want a super job put rockwool addtionally in between the joists
Chris
correct
The point is to ckeep most and cold separate.
Since both are needed to get condensation.
Think roof rafters They are all on the cold side..
If you use foil-backed Celotex (or Kingspan, which IME is more robust), and tape the joints over the joists with foil tape, then you have installed a vapour barrier.
Regards Richard
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