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Guidance on insulating cellar ceiling

Postby s.w.webb1 » Tue Jan 05, 2021 10:55 am

We have a cellar (2.7m * 2.6m) below our kitchen, currently there is 40mm SuperQuilt stapled to underside of the floor joists between the cellar & kitchen (not installed particularly well by the looks of it - lots of air gaps, no tape on joints etc).

I'd like to be able to board out the ceiling in the cellar to give it a bit of a better finish, but ultimately it's only for a workshop, not for a livable room.

What approach would you recommend? I'm leaning towards replacing the SuperQuilt with insulation I can fit between joists (wool type or celotex/board type) & then fix the plasterboard straight to the joist. Joists are 160mm. What level of insulation would I need to provide & do I need it to be backed with a vapour barrier? Do I need an air gap above/below the insulation?
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Simply Build It

Postby stoneyboy » Wed Jan 06, 2021 9:58 pm

Hi S.w.webb1
Probably easiest to fit expanded polystyrene between the joists. Hold it in place by fixing battens to the joists under the sheets. Leave a gap above the sheets for services.
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Postby B4Less » Mon Jan 25, 2021 3:24 pm

Yes, I would install insulation between the joists, but then I would also put back up the superquilt before you board over. No need then for vapour plasterboard. Make sure you tape the joints of the superqiuilt this time. Also, airflow is essential so might be a good idea to have two air vents 1 in and 1 out and counter batten your ceiling so your air can move around. This will avoid any buildup of condensation.
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