Best minimal Insulation options for Bathroom

[Ed21]

HIya, 

Got a fully tiled small bathroom and want to add some insulation on the inside of the outer wall which is cavity. 
It will have an extractor, but going to be a lot of warm water and condensation.

Plan was to use thicker foam cement tile board of around 30mm*, but as these are XP was thinking if it would i
be better to go for 25mm PIR on the wall and use 6mm or 10mm backing boards on top.
Same thickness just better insulation.  

Any issues with the second approach? 

Rgds Ed

*About the thickest I can get away with 

Edited March 1, 2021 by Ed21

[SteamyTea]

Stick to building regs

https://www.planningportal.co.uk/info/200135/approved_documents

Edited March 1, 2021 by SteamyTea

[MikeGrahamT21]

22 minutes ago, Ed21 said:

HIya, 

Got a fully tiled small bathroom and want to add some insulation on the inside of the outer wall which is cavity. 
It will have an extractor, but going to be a lot of warm water and condensation.

Plan was to use thicker foam cement tile board of around 30mm*, but as these are XP was thinking if it would i
be better to go for 25mm PIR on the wall and use 6mm or 10mm backing boards on top.
Same thickness just better insulation.  

Any issues with the second approach? 

Rgds Ed

*About the thickest I can get away with 

 

The problem with PIR is you need to physically fix it with mechanical fixings, which will give thermal bridging. Your better off with a 30mm cement tile board such as marmox which can be fixed using tile adhesive alone (though check with manufacturer to be sure)

[nod]

45 minutes ago, Ed21 said:

HIya, 

Got a fully tiled small bathroom and want to add some insulation on the inside of the outer wall which is cavity. 
It will have an extractor, but going to be a lot of warm water and condensation.

Plan was to use thicker foam cement tile board of around 30mm*, but as these are XP was thinking if it would i
be better to go for 25mm PIR on the wall and use 6mm or 10mm backing boards on top.
Same thickness just better insulation.  

Any issues with the second approach? 

Rgds Ed

*About the thickest I can get away with 

As long as the foam on the back of the insulated plasterboards is pink in colour You can use drywall adhesive to fix it to the wall Then tile directly Onto it 

[Ed21]

Thanks for the replies guys 

Ok looking at it again wall has been cement rendered above a bath (coming out), but not below. 
It's got two layers of tiles and window is coming out + it's needs an extractor & will have one big
shower instead.
Think best to take the lot off back to brick/flat screed and that saves 15/20mm. With render and
tiles gone that means can boost the  thickness and use 50mm Marmox or cheaper Q Board.
So XP thicker than was going for with a 6mm board/25mm PIR sandwich and should rum out at
about the same. Can stick this on so no breakthrough ?

Ed

Edited March 1, 2021 by Ed21