Heat loss from pitched roof in garage conversion

[lorry75]

Hi, we had the garage converted about a year ago to add space with an open kitchen dining room. Since its been done, its always been cold. Floor was floating floorboards, chipboard then underlay, laminate flooring. jablite insulation laid over concrete floor and a dpm. Blockwork added to the to the external walls and the cavity wall filled with rockwool. I know the pitched roof was fitted with 50mm celotex pir board, 12mm plasterboard but it still doesnt seem to be well insulated enough.there are also 2 velux windows fitted. We get alot of sound leakage and it can loss 6 to 7 degrees heat loss overnight, on really cold nights in the far end of the extension. The other morning which was a frosty start, i took a few pictures before the heating came on, to see any heat spots on the roof. ( back of the house not south facing) Which there was, could this be down to poor insulation around the velux windows, or poorly fitted celotex boards, (not taped, openings for downlights) ive attached some pictures. We do have the boiler in the garage blowing off over the side of the garage conversion, but dont think this the reason for the frost melting at the front of the extension it looks to me like heat leakage is coming from inside.

Can anyone give advice on what would be required to fix this.

 

[Alastairreid]

Vaulted ceiling? you need 120mm insulation as a minimum, floor 100mm.

 

[foxhole]

Where I used celotex insulation in roof space I used 125mm.100mm between joists and 25mm over the top .

 

[lorry75]

Thanks for the replies. Yes it is a vaulted ceiling, I'll double check on the celetex board measurement, as not 100% sure now if it was 50mm. Ive found pictures from when it was getting fitted and the off cuts look bigger than 50mm. If this is down to the thickness of celotex, would this be easier taking the roof tiles/membrane off and doubling up on the insulation from above or just opening up the plastered ceiling below and adding from below, obviously more mess and cost for plastering.

 

[lorry75]

Hard to tell just now without getting back on the roof, but in this pictures the offcuts look bigger than 50mm.

 

[Mr Chibs]

I've a recent vaulted ceiling with three velux... I too put 100mm in between and another 50mm after (inside), can confirm it's warm.
I've also got a suspended wood insulated floor, with rockwool.

Yes, at a quick glance it looks smaller than 100mm... my guess is 70/80mm

 

[Mr Chibs]

You'll probably need to keep the air gap beneath the roof membrane, and therefore your rafter depth will determine what room you've got left for insulation, from memory my air gap is 50mm, so 100mm of foam fits nicely in a 150mm rafter.

Not sure which I'd like to do most, tiles off of plasterboard... have you got head height to add more celotex to inside? any lights in the ceiling??

 

[lorry75]

I'll have a look when i get home and see if i can get measurement of the rafters and the depth of the celotex boards. We definitely have the head height to add addition insulation from below. We do also have downlights fitted.

 

[lorry75]

Measured the exposed rafters in the front end of the garage and they are 150mm, trying to measure the pir board through the downlight hole, this is coming in around 80mm.

 

[catlad]

I fitted a large flat roof skylight just before christmas and when I came down at the end of the day the sparky had
put 6" holes in the kingspan everywhere to accommodate the spotlights!!!
The easiest solution would be to fit insulated plasterboard over your existing ceiling at this stage.
And then Bill the person who built it.