Is this BR-compliant for garage conversion walls?

[Gooman]

I saw this suggestion on another site, and it looks like a good shortcut but I have doubts as to whether it would pass Building Regs ... any opinions?

 

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Start by sticking the cellotex to the walls and taping the joins with waterproof tape. A blob of ‘no nails’ in the top corners should hold them up while you work. Then install the cellotex for the floor. Then install the chipboard on top. Then fix battens through the wall cellotex into the brickwork (so the battens sit on the chipboard floor) and screw plasterboard over the top. Taping the joins of the cellotex makes the cellotex itself the vapour barrier so no need for another sheet of plastic.

 

It would save time as there's no cutting of PIR to fit between battens (and arguably gives slightly better insulating properties).

 

Wiring could be fixed in conduit taped or glued to the PIR before fixing plasterboard.

[ProDave]

Wiring would go in the battened service void between the celotex and the plasterboard. No need for conduit unless you want it.

[andyscotland]

I'm currently doing a garage conversion - single skin pebbledashed blockwork. Ecotherm advised that for my construction it would be better from a damp/condensation risk perspective to batten the insulation away from the wall. Their dot and dab detail is more designed for cavity walls. So 25mm battens fixed through strips of DPC into the block, then continuous PIR, then another run of 25mm battens screwed through to the battens behind, then plasterboard.

 

I submitted it with Ecotherm's u-value and condensation risk calcs and didn't get any questions from building control (in Scotland) at the plans stage.

 

As you say it does make a fair difference to have the insulation continuous without thermal bridges.

[Gooman]

Answering my own question ... I contacted Celotex technical, and they say that although normally they wouldn't advise putting PIR straight onto a wall <200mm (this is a single-skin 100mm wall), as this is a party wall and isn't strictly external the dot&dab approach should be fine.

 

Which is great, as it will save a lot of time and avoid any thermal bridging.

[PeterW]

Don’t bother with adhesive or dot and dab - get a couple of cans of the low expansion gun foam and a plant sprayer with water in it. 

 

Squirt a line of foam on the boards, then spray it with water and leave for 5-10 mins to expand. 

 

Then lift the board to the wall and the foam will bond the board on. Also foam between the board edges and it’s not going anywhere. 

 

Battens can be added once it’s all gone off. Foil tape the joints for good measure - what are you doing about  the ceiling ..?

[Gooman]

New roof on the part of the garage that's being converted, as otherwise the ceiling will be too low. Leaving that job to my builder.

[PeterW]

Ok but how will you tie the ceiling insulation to the wall insulation ..??

[Gooman]

TBC, but likely a cold-roof with PIR between joists and PIR/plasterboard combo over, sealed at the edges joining with the wall insulation.

 

So order of build is likely to be:

• New roof construction
• Insulation on walls (dabbed)
• Insulate between ceiling rafters and run wiring for ceiling lighting
• Insulate floor + chipboard
• Insulate ceiling with PIR/plasterboard and seal all joins
• Battens to walls and fix plasterboard

[Gooman]

Further answer to my own question ... local Building Regs folks have advised me that I will need sound insulation between the new room and the garage next door. A 10mm stud wall with PIR board on top (not between) will provide this.