Critique my insulated drylining approach

[Daveo119]

Hi,

I'd like to add some insulation to the external walls in a 1930s semi with uninsulated brick cavity.

I though the best method would be to remove the existing, heavily patched, lime plaster. Assuming the walls are flat enough:

50 mm foil backed PIR
Tape seams and expanding foam around perimeter
2x1 untreated batterns, 3x1 if I can get them
Long screws through batters and insulation
25mm PIR
12.5 mm pb

I'm not keen on d&d as I've never done it and seems more likely I'll end up with an even wall.

If the walls are bad i could go with treated 3x2 batterns on the cold side and pack them level? 50mm PIR infill?

Parge coat needed with a cavity?

Cheers,
Dave

 

[PrenticeBoyofDerry]

If the question is if to or not to parge coat, if you are battening out why would you think a parge coat would be required?

 

[Daveo119]

An excellent question, I've read it before but it was in relation to a solid wall.

Maybe I should have put it differently, what's the best method to insulate in my case assuming I get a pro to skim?

 

[PrenticeBoyofDerry]

The best way if possible would be to insulate externally, therefore not reducing sq footage in property, but this not always practical.
Your suggestion seem fair, but ideally I would prefer 50-75mm thermal insulation.
You could build either timber or metal stud along the external perimeter wall, these walls do not need to come in contact with the external wall but built just off it and fixed at floor, ceiling and end walls. Then the cavity between wall and stud can be insulated, then either board with foil back or put up a vapour check barrier for good measure.