Insulating a bedroom floor from below?!

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Hi all,

I have a 1960s bedroom extension above a very cold garage below, in my 1930s semi. Looks like the people who put the bedroom extension in didn't bother insulating the floor... so it's freezing in winter and no doubt massively leaking heat!

The bedroom has stripped and polished floorboards, they are all in good condition and seem to be original from the 1960s - so I'm a bit loath to damage them by tearing them up to install insulation from above.

I wondered whether it was feasible to do it from below? There are standard 9.5mm thick plasterboards on the ceiling of the garage, I've tried removing a few joist screws and they come out fine.

Would it just be a case of installing strips of Rockwool or similar, taping them in place if necessary, and then screwing the plasterboards back on?

** Is there a need for a damp proof membrane on the top of the joist spaces, ie. just below the floorboards of the bedroom? Would this be a problem because the tops of the joists are not accessible?

** Is there a need to install additional insulation sheets across the bottom to prevent thermal bridging of the joists? Would this prevent the ceiling plasterboards being screwed back on, due to the increased depth?

** Part of the bedroom has an en-suite bathroom which has a tiled floor, and from below there are various pipes on the garage ceiling which will make it very hard to remove the ceiling plasterboard. If I don't insulate below the bathroom, does that make the whole project pointless because all the heat will continue to rush out of the bathroom floor anyway??

Has anyone done this sort of job before??

Thanks very much for any tips!
 
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yes it perfectly possible to do that

Im not sure if you have to use fireproof material like rockwall

if you dont Id be tempted to use actis hybris insulation as its so easy to fit
 
If I don't insulate below the bathroom, does that make the whole project pointless because all the heat will continue to rush out of the bathroom floor anyway??
No. Heat rises, I doubt it's "rushing" out of the floor. Gaps that let draughts through would probably be more likely to cause a loss of heat than heat being conducted downwards.

As to the general point, yes, doing it from below is going to be a lot easier. I am sure that disrupting the garage by taking the ceiling down is a lot easier than disrupting the bedroom and bathroom by taking up the floor. Just hope it really is plasterboard and not asbestos insulating board :)
 
WNI thanks, yes good point about AIB I hadn't thought of that! I might need to send a sliver off for asbestos testing :(
 
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WNI thanks, yes good point about AIB I hadn't thought of that! I might need to send a sliver off for asbestos testing :(

Plasterboard is a pale pink colour and much softer than asbestos and has a paper/card at both sides - you can poke a hole in it with just a screwdriver. Asbestos is grey and a harder surface, it would need a drill to make a hole in it.
 
Your existing should be two layers of plasterboard or fire resistant board to comply with regs, 9mm board seems inadequate .
 

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