Minimising the thickness of dormer cheeks / sides

[rockmc]

Our builders are about to start work on our loft conversion. We have planning permission for two 180cm wide front dormers and we're keen that the sides / cheeks of these are as slim as possible to maximise the window space within.

Our architect has specified the following:
"Clad with clay plain tile hanging on battens on Tyvek SUPRO Plus on 12mm WBP Ply lining fixed back to 100 x 50 studs @ 400mm c/c. 100mm Celotex GA3000 between studs. Holes drilled in ply to improve ventilation"

The local building control inspector has accepted these specifications as meeting appropriate regulations.

I'd be very grateful for any recommendations of alternative materials / solutions which would still meet the regulations but allow us to reclaim more space?

Thanks very much.

 

[freddiemercurystwin]

You won't get much thinner than that, sounds perfectly reasonable to me. Maybe shave the timbers down to say 75mm if 75mm insul still meets the regs which I doubt but then they'll be getting a bit thin structurally. I really think its fine as it is.

 

[rockmc]

With the existing specification, how thick do you each wall would end up - taking into account tiles, plasterboard etc?
Thanks

 

[freddiemercurystwin]

! About 175mm.

 

[rockmc]

thanks very much for your help

 

[Chri5]

Each cheek will end up with 2mm plaster skim, 11mm plaster board, 100mm wood structire, 12mm surface sheet.

125mm

Then the baton and finishing surface tiles approx 40-50mm.

Have you thought about having the cheeks clad in lead ?

 

[rockmc]

I was considering zinc - looks like that will save me 20-30mm - is that right?

Also, the Building Control inspector told me today that he would accept Triso-Super 10 instead of the Celotex GA3000 for the dormer cheeks. Regardless of the merits of the product itself, it is clearly significantly thinner. Presumably the construction (specifically the 100x50mm studs) would need to be changed for me to benefit from this reduction in insulation thickness.

 

[freddiemercurystwin]

I was considering zinc - looks like that will save me 20-30mm - is that right?

Also, the Building Control inspector told me today that he would accept Triso-Super 10 instead of the Celotex GA3000 for the dormer cheeks. Regardless of the merits of the product itself, it is clearly significantly thinner. Presumably the construction (specifically the 100x50mm studs) would need to be changed for me to benefit from this reduction in insulation thickness.

Triso-Super is accepted by some BCs and not by others, as you say, the jurys still out on it! However as mentioned already you still need the timber studs anyway which you could maybe shave down a tad. You could change the tiles to something slightly thinner but really, does 25mm or so make that much difference? You're one of those pain in the a*se clients aren't you?

 

[rockmc]

I think I must be! Just been looking around at dormers that I feel look nice and they're all 100 years old without any insulation!
Thanks for the advice.

 

[Shytalkz]

Also, the Building Control inspector told me today that he would accept Triso-Super 10 instead of the Celotex GA3000 for the dormer cheeks.

Ahah, so sensible ones - other than Mikric - do exist then.

 

[freddiemercurystwin]

I think I must be! Just been looking around at dormers that I feel look nice and they're all 100 years old without any insulation!
Thanks for the advice.

And damp and cold inside, nice!