Insulating pitched roof which already has some foil quilted insulation above the rafters

[gtawebb]

Hello, I'm looking to improve the insulation in a bedroom.

I was planning on adding rigid foil backed insulation between the rafters and then over boarding it with insulated plasterboard.

I have now cut into the ceiling to check rafter depth and I've found that it already has some quilted foil membrane / insulation (superquilt?) above the rafters. Unfortunately the rafter depth is only 3 inches.

Is it ok to put rigid insulation between the rafters under the quilt and would a ventilation gap be need between the two layers. If so this wouldn't leave me much insulation depth!

I had previously been hoping for 50m ventilation gap with 100mm rigid insulation between rafters and then 37.5mm insulated plaster board.

I think I might need to now go for 25mm ventilation gap with 50mm rigid insulation between rafters and then 37.5mm insulated plaster board. At least the quilted layer should also be helping?

Any suggestions for the best way forward would be much appreciated. Photo attached.

Many thanks.

 

[JohnD]

Is this a habitable loft conversion you mean?

 

[gtawebb]

It's already a bedroom, I'm just looking to improve the ceiling and wall insulation as it is difficult to heat the room effectively.