how to insulate a semi-external block wall

[ps]

Hi,
I have a 1920's house with attached garage which has a single pitched roof.

This roof void is used as a walk-in loft space, accessed via my sons room on the first floor. This wall (between my sons room and the loft space) is only of single block construction, and therefore makes my sons room very cold.

I want to insulate this single block wall on the loft side (because my sons room is already decorated etc).

1) Which thermal board would be appropriate? Since I'm going to all the effort I might as well get the u value down to approx 0.3; so I'm guessing ti will have to be at least 50mm.

2) With regards to interstitial condensation, should I use a VCL, or simply attach the PIR boards to the block wall on wood battens, thereby leaving a small air gap for moisture to drop down. I've had conflicting reports.

many thanks

[ps]

does anybody have any ideas, as I'm still getting conflicting reports.

One company for eg, said I should leave a small air cavity between insulation and wall to let moisture run down.

Quinn Therm said that I should fix their boards directly to the wall and tape up to form a VCL.

I've contacted Celotex today, but haven't got a reply yet.

Any further thoughts anybody?

[Quint1983]

Hi, SuperQuilt on battens will give you a u-value of 0.32, this is what i have just used. very easy.
Cheers