Insulation - Does 100mm + 50mm = 150mm

[ecopod]

Hello to all,

I'm putting 150mm full fill insulation (Kinspan/Celotex) between rafters. I can get a load of relatively cheap 100mm Kinspan (K7) and was wondering if BC is okay with adding separate 50mm layer - 32.5 insulated plasterboard will go over the top. Only other factor is all boards are foil backed so at the sandwiching face foil will be touching foil.

Many thanks in anticipation.

 

[noseall]

No problem. Be sure to fit the boards as snug as possible.

Why the full fill?

The usual scenario is to leave an air gap on the cold side, say 25-50mm, so that moisture rich air can be dealt with either via breathable roofing membrane or vents.

A typical detail would show 100mm between the rafters with a further 40mm underdraw.

 

[Chukka63]

im currently installing 75mm between and 50 below the rafter and 12.5mm plasterboard.

 

[ecopod]

Thanks for quick replies.

Full fill is specified by architect, using breathable membrane on 18mm sarking and insulation pushed right up to sarking. Actually putting in a couple of 140's as I need a couple of cables run in ceiling.

 

[PrenticeBoyofDerry]

Don't forget to have cable calcs done, for any de-rating of cables that are totally surrounded by insulation. As this does effect the current carrying capacity of cables.

 

[ecopod]

Prentice, thanks for pointer. I'm planning on doing as much of the inside work as I can but the electrics are being left to the pro's.