Extension insulation

[chuckalicious]

I have had a small extension built which has a vaulted ceiling.

The roof insulation installed was some form of Celotex foil backed stuff that was fairly thick.

However we have found that although it heats well, it cools down very quickly, more so than the rest of the house. Having seen the amount of insulation in the build I had expected it to be like a hotbox.

This morning when I went out I noticed that my main roof (which isn't vaulted and is insulated with glass wool) was frosty but the extension was wet. Could this highlight an issue?

 

[John D v2.0]

Probably the air is just circulation around the celotex. So it's not doing anything.
Rather like sitting next to a warm duvet, you have to wrap yourself to keep warm.
Basically need to seal all the gaps round the edges for it to do anything.

 

[chuckalicious]

Not what I wanted to hear. Is this something I should be raising with the builder?

 

[John D v2.0]

Yes you paid good money for the insulation and it's not doing anything. Failing that you can get someone else's to fix it.

 

[chuckalicious]

I've sent him the photo but I cant imagine he will say anything other than that is normal. To say otherwise would mean he would have to fix, put new plasterboard up, replaster and then redecorate.

 

[chuckalicious]

He has replied saying as there is no ceiling in the extension even with the insulation there will be a bit more heat loss than the rest of the house, which has a ceiling and thus a big, vented gap between it and the roof itself, which would explain the difference.

He suggests raising the issue with the architect....

 

[John D v2.0]

It's true, but that wouldn't make it cool down quickly. Unless the walls are internally insulated, there should be plenty of thermal mass.
An idea, on a windy way get some smoke pen (incense or something) and see where the air currents are going in that room. Maybe there are actually draughts behind the plaster board going up there.

 

[chuckalicious]

The construction, from inside to outside is plasterboard, block, insulation on outside of block, cavity, brick. Should be plenty of thermal mass there I'd hope.

 

[chappers]

But your little extension stuck on the side of your house has loads less mass and when heated contains loads less heated air so will cool much quicker.
By the exact method described by your builder which is correct

 

[chuckalicious]

But your little extension stuck on the side of your house has loads less mass and when heated contains loads less heated air so will cool much quicker.
By the exact method described by your builder which is correct

It certainly makes sense, maybe I was just hoping for too much. Would that still.explain the warmer roof?

 

[datarebal]

how thick was "fairly" thick?

 

[chuckalicious]

how thick was "fairly" thick?

Still have some in the basement. Will measure and let you know.

 

[John D v2.0]

But your little extension stuck on the side of your house has loads less mass and when heated contains loads less heated air so will cool much quicker.
By the exact method described by your builder which is correct

It's the mass to external area that matters, the air has little thermal mass. However good point that there's more roof:wall ratio, do you think that would be so noticeable?

 

[chuckalicious]

Architect also agrees with the builder (the 2 are not connected) so I guess that's how it is and I was just expecting too much.