Insulate ceiling or not?

paddylonglegs

hello folks,

our 1970s bungalow had to be reroofed. New frame, new tiles etc, and new pitch to allow us to use upstairs as bedrooms.

The new roof will be getting insulated - 100mm rigid king span between rafters, and 50mm warm board over rafters is the advice.

Because the upstairs will now be getting used as habitable space, do I avoid insulating between the joists in the ground floor ceiling/upstairs floor? This had been insulated before the reroofing and thought it wouldn’t do any harm, but now I’m thinking it will prevent the upstairs getting heated and draw the heat upstairs when rads are on downstairs? There is the usual void at the stairs so I expect this will draw heat up.

So do I avoid insulating this area or does it really matter?

Any thoughts on this?

GreeBo

You only insulate (for heat loss!) on the exterior envelope of the building, so you would insulate your "new" floor.

You might use internal insulation for noise reduction however.

Is there a source of heat in the new space, if its a habitable space then it will need some source of heating or you will get a cold breeze coming down the new stairs as the warm aim comes up.

Presumably not all the roof space will be a warm space, where are are the water tanks etc. going and what prevision will there to be stop them from freezing and also keep the remaining cold space well ventilated?

Are you doing all the internal insulation yourself? If so, whats the plan for VCL and ventilation in the new space? The rafters will need to breathe behind your rigid insulation and you will need to use excellent detailing with foil tape etc. to prevent condensation, especially if you have no heat source up there.

Finally, if its going to be bedrooms then you need to met all the regulations etc. regarding fire safety.

Doop

If its already there I would leave it in situ, it will help with noise reduction. Presuming the new upstairs rooms will have their own heat source (rads). Ideally you want to keep the heat in the room it is created it. Ie the insulation will help the living rooms below stay warm.