Dormer insulation

[Steveshouse]

I am in the process of insulating my dormer, the cheeks consist of tile - felt ( I don't know if it is breathable - is there a way of finding out?) - thin covering of wool insulation - then stud 50mm deep.

I would appreciate advice on the triangle bit of the cheek It is 50mm deep and I would like to put in 50mm celotex but am unsure if I need an air gap?

I am also insulating the walls to the eaves and was wondering if putting 100mm wool in the stud and covering with 25mm celotex then 12.5 vc plasterboard is ok? Am I ok to stick the 100mm to the purlin (photo uploaded)

Many thanks
Steve

 

[tony1851]

For the main walls of the dormer, if your studs are around 100 deep, put 100 quilt between, and finish internally with vapour barrier stapled to joists, 25 Kingspan (or equiv.) and plasterboard + finish.

 

[Steveshouse]

Thanks for the reply would i be ok sticking the quilt to the purlin which runs across the back of the stud work?
Also, would you know if the cheek would be ok with no air gap or should I leave 25mm air then 25mm celotex in the stud then 25mm over stud then vc pb

Thanks
Steve

 

[tony1851]

Thanks for the reply would i be ok sticking the quilt to the purlin which runs across the back of the stud work?
Also, would you know if the cheek would be ok with no air gap or should I leave 25mm air then 25mm celotex in the stud then 25mm over stud then vc pb

Thanks
Steve

The exposed dormer cheek should be insulated to the same standard as the front. Two x 25 kingspan will not comply.

 

[Steveshouse]

I want to put 50mm between the stud then 25mm over stud and 50mm making it 75mm in total my concern is do I need an air gap. I can't put anymore studding on as it would come over the window
Thanks
Steve

 

[tony1851]

I want to put 50mm between the stud then 25mm over stud and 50mm making it 75mm in total my concern is do I need an air gap. I can't put anymore studding on as it would come over the window
Thanks
Steve

Don't need an air gap anywhere. Just a vapour barrier on the warm side of the insulation.

 

[Steveshouse]

Thanks for the speedy reply Tony
I will fill the space with 50mm celotex cover with 25mm celotex then 12.5 vapour check plasterboard.
Just going back to previous post will I be ok putting the quilt up against the purlin then 25mm celotex then 12.5 vapour check plasterboard

Thank you
Steve