Insulating Garage Ceiling

[Twin Dad]

Hi All,

I know the topic of insulating a garage has been covered many times but I can't find the answer I am looking for so here goes.

I have a garage with a room above. The garage ceiling is boarded in fire retardant sheet to provide protection to the room above. Unfortunately the void between the ceiling and the room above is not insulated.

I know that I could take up all of the carpet and T&G chipboard above, stuff it with the itchy stuff and then replace everything but that would actually be quite a bit of disturbance. From a building regs, safety or general practically point of view, is there any reason I couldn't overboard the garage ceiling with celotex or similar, leaving the fire proof board in situ thus maintaining fire protection for the room above. I would probably stick the PIR up temporarily with spray adhesive and then mechanically fix through the PIR, through the fireboard and into the ceiling joists. Tape and seal seems between boards.

Thanks in advance.

 

[^woody^]

is there any reason I couldn't overboard the garage ceiling with celotex or similar,

Yes, because it would be silly.

That's insulating the cold garage, which will do zilch. You still would have the cold floor void with a gale blowing thorough it. This has been discussed numerous times, the insulation needs to go directly under the floor deck to insulate the room.

And that's increasing the fire risk in the garage as celotex likes to burn.

 

[Twin Dad]

Yes, because it would be silly.

That's insulating the cold garage, which will do zilch. You still would have the cold floor void with a gale blowing thorough it. This has been discussed numerous times, the insulation needs to go directly under the floor deck to insulate the room.

And that's increasing the fire risk in the garage as celotex likes to burn.

Thanks Woody that is exactly why I asked. Fire risk is/was my main concern. If its a floor up job then so be it. It won't be the first time. Why though would the floor void be cold/have a gale blowing through. Where would that come from. Sorry if this is obvious, I can't visualise it. Thanks.

 

[^woody^]

There will be gaps around the joists and air will be leaking into and out of the void via the floor or ceiling too.

 

[Twin Dad]

There will be gaps around the joists and air will be leaking into and out of the void via the floor or ceiling too.

That's the bit I can't see. If the joists sit on hangers inside the walls, where will the cold air come from I had insulated below? The ceiling void isn't open to the elements. I can't visualise it but you're not the first person to say this, I'm sure its right - but it's bugging me.

 

[^woody^]

If the joists are on hangers then the chances of air gaps into the walls reduced, or removed. But there is still air leakage from any floor void which means it will be cold and draughty, and that is what needs to be dealt with by insulation within the void.