Partition walls - Insulate or not?

23 Sep 2015
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United Kingdom
Hi all,

My first post here, so thanks in advance for any tips.

I am currently upgrading my late 1960s bungalow. It has had two extensions in its life, both to the rear and the latter is a granny annex that sits below the ground floor on ground sloping away from the back.

Anyway, I am creating a kitchen diner and small bathroom in the annex and am unsure as to the best way to insulate it. I have 100mm of PIR foam insulation for the roof (cold flat roof with balcony area) and will have a 2" air gap below that for services and then plasterboard. I have also got some 1" PIR boards if I decide to put this above the plasterboard. The biggest problem is headroom, with only 2.1 ceiling height at the moment, I am limited to what I can install, particularly as the floor is to have an underfloor heating system installed.

The partition walls are 100mm concrete block and one of the bathroom walls consists of the original footings of the bungalow and concrete blocks, only the narrow end of the bathroom has Celcon blockwork (inner and outer, 2" cavity no fill). I had initially thought that insulating the partition walls with 25mm PIR would be a good idea to keep the bathroom toasty, but is there really much point and would a simple air gap between the 1" stud work and tile backer be sufficient?

Thanks again.
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