Insulation in Rafters

[BigHammo]

I have a small kitchen extension with a pitched roof (6M x 3M). My Building inspector has told me to install 100mm board insulation, in the rafters and 25mm insulation boards across these boards.

He also told me that I didn't need to insulate the joists. Having spoken to a few people, they said that this seems strange. Is this correct? I will have silver backed plasterboards on the ceiling and the insulation is silver backed both sides.

Cheers

 

[bondy]

when we build extensions with pitched roofs, we ALWAYS put 100 rockwool between joists and 150 rockwool across the first layer. the second layer is layed at 90 degrees to the first. this is accepted by our local building control office. (welwyn and hatfield. hertfordshire.)

 

[Static]

Are you using the loft space for bedroom etc??

 

[BigHammo]

No. it is a single story kiychen extension.

 

[Static]

You placing them between rafter (pitched timbers) or ceiling joists ?? if joists then thats normal

 

[BigHammo]

Rafters

 

[JohnD]

You will be using twice as much insulation to keep the loft space warm. I wonder if the inspector thinks that you will later want to use it as a habitable room? Is it big enough for that?

 

[BigHammo]

It is not big enough to put another room in. It also a 20 degree pitch 2.4 metres by 6 metres. So it is quite small. I am probably going to have to cut the kingspan to get it in the tiny space is this acceptable?