Hi. I'm after some advice on methods of installing insulation board behind plasterboard. I've just removed a fitted wardrobe from an external wall of my 1940s semi and the plaster behind was blown so I've removed it back to brick. It's a cavity wall on the first floor and appears to be dry. As it's an external wall I want to insulate it internally before plastering. From what I've read the usual way to do this would be either to install battens and then insulate between them and plasterboard over the top, or dot and dab insulation backed plasterboard. However, I got a plasterer in to quote for the job today and he said he would use separate insulation board (Kingspan or similar) which he would sandwich between the wall and plasterboard, using mechanical fixings through both plasterboard and insulation into the wall to hold them in place. He would then skim over the top. He says he's used this method in his own home. As everything I've read on the Internet talks about either dot and dab or battening (both of which presumably leave a gap between the wall and insulation) I'm wondering if his method is just cutting corners or is a sensible approach. Is there any problem with not having a gap? Are there any other problems with this method? Any advice much appreciated!
Using the battens has the advantage of being able to shim them out to create a perfectly plumb wall when finished, but doesn’t provide the best insulation value. If the wall is reasonably level, fixing plasterboard over sheets of kingspan is my preference, it’s certainly not a corner cutting exercise as it presents more complications but costs less in materials and labour time. If your plasterer is suggesting this method and you’re happy with his quote, go for it.
Thanks Hausfix. That puts my mind at rest, it just seemed strange that it isn't suggested as a method anywhere that I can find. I wondered if the need for more fixings meant more cold bridges which might be an issue? I will probably go with the quote as like you say it's cheaper in materials. I'd be interested to know what the additional complications it presents are that you mention? Many thanks.
The complications are mainly due to the method of fixing. Screwing drywall screws straight into timber is simple, however, having to drill trough the plasterboard and insulation whilst holding it in place, then knock a wallplug in and then fix with a long screw all without damaging the delicate plasterboard surface dozens of times isn’t easy. Cold bridging through the surface area of the timber battens is far greater than the screws.
I usually have a spade blade under the bottom of the plasterboard, step lightly on the spade handle to lift the board into place, move the handle with your foot left and right to position the board. Or you could use the proprietary tool. My preferred method is to batten and insulate between with a vapour barrier over. That allows shimming to level and provided fixings for future use every 600mm.
It occurs to be that there is no facility in his method for trueing up the wall surface which battens or d&d would both give. (Of course you might have perfect walls already)
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