Garage roof insulation - why?

[Adam2]

Quick one - my architect has spec'd sloping insulation in the garage roof - it will NEVER be converted into a "room". A - sloping = more costly vs the timbers being at an angle so that's mad and B - why even think about this? To me seems a bit odd as the construction is regular single skin blockwork with the side against the house being the house's ICF exterior wall. It will house 1 of our MVHR units but I checked and the supplier says no problem in a regular garage. I would have thought that a garage constructed like this would get to external air temp quite quickly with or without an insulated roof as the double door will not be anywhere near air-tight.

 

Am I missing something in my understanding?

 

This only came to light when I asked for a drainpipe to be moved and saw the detail in the roof structure.

 

Thanks

[joe90]

What’s the roofing materials?, could be to stop condensation dripping inside. I used roofing felt under my metal roofing on my garage to stop any condensation dripping on my tools etc.

[Adam2]

Alwitra - single ply membrane I believe. I will of course ask them for reasons but wanted to quickly check here first

[scottishjohn]

attached to the main house  would my guess why it has to have  an insulated roof

[ADLIan]

If attached garage but unheated then no need to insulate roof (or floor or ext walls)

[mvincentd]

My architects also seemed to have particular difficulty unhooking themselves from the idea of future proofing the garage roof. I think they see it as a harder retrofit than insulating the walls.

[Adam2]

Thanks- will change this and save some money and time :-) Much appreciated

[scottishjohn]

so if this roof is  going to be a flat one  ,then one would presume its a GRP  skinned type 

tin roof needs a bigger slope or it won,t work  correctly 

so if it  is osb +grp and no insulation --you could easily get condensation on the OSB inner skin -- not a good idea 

I know cos that how my garage was built --hellish hot in summer and cold as hell in winter-I got seconds +co insulation and jammed it up between the rafters --

much more civilised now and no freezing of tap in there ,then bursts  in garage in winter 

the taper insulation does not give a big slope ,certainly much less than you would need with a tin one  and cuts out condensation problem 

something to ponder 

 

[mvincentd]

22 hours ago, scottishjohn said:

presume its a GRP  skinned type 

He said Alwitra, and given the sloping insulation spec I’d guess it’s warm roof construction....possibly in line with rest of house.  So maybe the insulation has to be outside the deck if at all.  I’d guess if tell architect to ditch insulation he’ll do a condensation risk analysis if any doubts.

[Adam2]

Thanks - very helpful info. @scottishjohn just not sure that only insulating the roof and  not the other 3 sides (1 side is against the house) will help with temp? Another factor is that the garage is mostly elevated - it extends out on a slope supported on a steel frame so the underside (beam+block) will get cold so adding to the argument I think that just insulating the roof may not make much difference