Insulation between batterns or old brick wall

G

GC129

Member
Heya, can't seem to find a conclusive answer on this online...

I'm boarding up external wall (in an ensuite behind the toilet) of a building which is 100 years old.

I have batterns on the wall to fix the plasterboard too.

If I use plaster board with a vapour barrier, what insulation can I stick in-between the batterns? From what I've read, something like polystyrene wouldn't be breathable and could cause issues.

Alternatively the wood fiber insulation looks like an option, but everywhere charges £70 for delivery!

Cheers!
 
I would use PIR (eg cellotex), If battens are 25mm, You may need to pack them slightly and then infill with 25mm PIR. If you have room for thicker battens or can double them up the more insulation you can put in the better. Lots more U value than polystyrene. As you say, use foil backed plasterboard .
 
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Thanks @Mark DM - would there need to be an airgap between the PIR and the external brick wall?

I know compressing insulation such as rockwall reduces its effectivness, but would putting that in between the batterns cause any damp issues? Insulation was more of an afterthought as it's only a small wall and very small ensuite so don't want to take up too much space!


Thanks @Larry_129 - didn't see they had those. Unfortunately I can't really afford to lose 100m of depth though.
 
If there is incoming air and its able to circulate and vent between the insulation and surface ( eg. Roof voids) then yes at least 25mm and ideally 50mm . However, if a wall is being battened and insulated and its sealed against the ceiling above and floor below and there are no damp issues then I see no point leaving a static void . Lined many external walls using this method usually with 25mm Inc around bay windows etc and never had any issues.
Rockwall slabs have around half the insulation value of PIR.
 
Look at kingspan k118 brochure, doubt you have put DPM under battens but never mind. As long as the plasterboard as some sort of VP behind and the external wall is resilient to water penetration damp should not be an issue.
 
Here's a photo of the wall, which is right up to the roof rafters.

There's quite a big hole around the soil pipe (not made by me...) on the internal wall, and an air brick on the external wall. Not sure whether it's best to fill this up with expanding foam or leave as is?

If air gap is needed, presumably acceptable to fix PIR onto batterns and then vapour plasterboard ontop of the PIR?

Hard to know if damp was an issue before as the previous installation had the extractor fan just extracting into a void between a stud wall and this brick wall...!! Hence the mould marks that can be seen on the wall here.

Thanks for the advice!
Screenshot 2024-03-13 at 19.21.07.png Screenshot 2024-03-13 at 19.22.07.png
 
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