Insulation for Attic room

I'm thinking of doing a DIY job on my attic room as presently it can be quite draughty. The internal finish consist of a 7-8mm grooved timber boards which are nailed directly to the rafters. There is a vapour barrier and only 150mm rockwool between the rafters.

I'm thinking the following:

1. Strip down the original timber boards.
2. Reinuslate.
3. Dryline using a 10mm gypsum boards.
4. Plaster.
5. Paint finish.

Could someone please recommend the thinnest insulation that could be fixed directly to the rafters, I could use in order to achieve the current building regs, best u-value. I have a height restriction in the attic of approx. 2m...so it needs to be some form of sheet insulation which I can lay under the plasterboard slabs

I would prefer not to remove the original vapour barrier\rockowool insulation, if possible.

Any thoughts, welcome

get this document

Thermal Building Regulations 2nd document
@ [broken link removed]

and [broken link removed]

Your looking for some sort of insulation backed plaster board to be fitted to the underside of the rafter.

For ease of installation I'm nearly sure you can get a 1200 x 600 board. From this laymans point of view you need to look at putting in at least the 2" insulation backed board.

davidoco said:

get this document

Thermal Building Regulations 2nd document
@ [broken link removed]

and [broken link removed]

Your looking for some sort of insulation backed plaster board to be fitted to the underside of the rafter.

For ease of installation I'm nearly sure you can get a 1200 x 600 board. From this laymans point of view you need to look at putting in at least the 2" insulation backed board.

Click to expand...

Thanks for that....I think the insulation between the rafters is 100mm moyisover (rockwool) with a 50mm air gap....I will confirm this later.

I would prefer to insulate it better...insulate,insulate,insulate....
Has anyone used a double layer of 50mm Kingspan insuation between the rafters.