Retrofit insulation to studwall fixed to external wall

[matw2]

I'm redoing a couple of rooms at the back of our property. It's flat with a few more above it, 1970s construction. The exterior walls (2 one room, 1 in the other) for these two back rooms very thick (est. 20-30cm) and strong concrete, as it is supporting 3 floors above it.

These walls had plasterboard sitting on a frame of 2 inch batons - with no insulation. I've removed the plasterboard, and going to put it back after new wiring goes in place. I had planned not to disturb the stud frame but just put mineral or natural wool insulation (50mm) in between the studs and then either vapour layer or vapour backed plasterboard. I understand this is not "optimal" as the existing frame might still cold bridge, but it will at least be better than what was there before (just an airgap).

However, some research suggests that it is not correct to put the insulation in so that it touches the external wall as the lack of an airgap is a problem for condensation: ideally I should be leaving an airgap between the existing wall and the insulation.

Frankly I'm now a little confused about the best approach to take. I would prefer not to increase the depth of the stud wall. Advice?

 

[ajrobb]

Crown DriTherm is a full fill cavity insulation bat. It is treated so it doesn't wick water from the outer leaf.

Don't bury wiring in insulation. I suggest you check in Electrics UK.

 

[matw2]

Hey, that's great - and I can see them my preferred supplier's site, even better.

I'm aware of wiring in insulation thanks to my copy of the IEE onsite guide, but always good to get a reminder.