DIY Doctor UK DIY Forums

Hi. Hope I'm posting this in the right forum group. Please move if not. Thanks.

We're renovating a room in our home that was previously converted by other occupiers. The room is dry lined but without any insulation apart from, possibly, cavity wall insulation. I plan to remove the plasterboard and insulate the wall before relining.
Question is that I want to maintain the width of the single garage width room as much as I can. Can someone advise on possible solutions? Thin Kingspan/Celotex perhaps? Superquilt type products with possible insulated plasterboard? Are there any downsides with the solutions I'm considering ie condensation? I'm a bit stuck with what to do next here and any advice would be really appreciated.

Hi temps,
Once you have stripped back to the original single skin wall you will need to fit a breathable membrane, battens, celotex or similar between the battens, at least 50mm celotex over the battens and plasterboard..
I'm assuming you are not applying for building regs approval.
Regards S

Morning Stoneyboy.

The garage was converted by previous occupiers more than 20yrs ago. Is it still necessary to apply for retrospective planning permission? The construction spec is cavity wall, brick and breeze block. I have had a look on the outside wall and there is no obvious sign of cavity wall insulation although I know the rest of the house does have it.

Bearing in mind the construction of the wall and the aim of me maintaining the width of the room so far as possible, would SuperFoil/Quilt be sufficient? Would I still need to put a breathable membrane in too as you suggested?

I appreciate the assistance.

Hi temps,
No need for planning, I was referring to building regs approval which you do not need.
Since you have confirmed you have cavity walls to your garage a breathable membrane is not necessary.
The easiest solution would be to redo the dry lining using plasterboard with insulation bonded to it. Don't forget to put a couple of screws in each sheet once the boards are in place..
Regards S

Standard PIR insulation like Celotex and Kingspan is the most popular option for this application. It has excellent thermal performance and relatively cost-efficient. If you're building a stud wall, the best practice is to insulate between and on the face of the studs with a thinner layer usually 25mm. The thinner layer on the face of the studs will help combat thermal bridging which occurs at each stud. A 25mm air gap is recommended between the insulation and the inner face of the external wall to combat condensation risk. Vapour controls layers along with associated tapes are recommended to the warm side of the insulation as an added layer to combat condensation build-up.