External bathroom wall insulation

[Steve82]

Hi

We have a west-facing bathroom wall which we have taken back to brick. We're confused about the best way to insulate the wall and reduce the risk of damp from the inside (or outside!).

The current plan is to build a stud wall (studs at 300mm intervals), fit Celotex in between the studs (pushed back and attached to the brick to leave an air gap) and then board out using 12.5 mm Marmox - taped joints and tiled from floor to ceiling.

Not sure if this is the best approach? Would I be better using a rockwool type insulation? Do I need to use a vapour barrier? I've been advised not to dot and dab Marmox boards in this case, but would this be an option?

The wall is double brick with a cavity.

Any advice will be gratefully received!

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[freddiemercurystwin]

Fit studs at 400 centres with foil faced Celotex or Kingspan in between. Fully fill the void, use as thick as insulation as you can afford/internal space are prepared lose but don't bother with any more than say 70mm. Tape the joints and across the studs with foil tape to maintain the vapour barrier. Behind the shower or bath or anywhere where else the tiles will get wet use Aquapanel. Elsewhere use moisture resistant plasterboard. Ensure a good extractor fan is properly installed and is used.

 

[Steve82]

Thanks so much for the quick reply! Because space is an issue we're thinking of making a 40mm deep stud and using 25mm Celotex board. Would it be worth filling the remaining space with another form of insulation?

We've chosen Marmox boards because they're "waterproof" and have inbuilt insulation - mainly worried about damp at the moment.

 

[freddiemercurystwin]

So use 40mm insulation in the 40mm void, no need for an air gap. No need for Marmox, Aquapanel is fine for all wet areas and MR is fine for everywhere else.