Dormer Party wall - insulate stud or brick

[Rnvte]

Dormer cheeks are stud, including an internal stud wall enclosing the chimney breast to sloped roof.
Query: Plans say to scratch coat existing party wall and install insulated plasterboard.
Builder says not necessary, insulate just stud wall and use fireboard.

Thoughts? Thanks

 

[Terrywookfit]

I asked Inspector what would be acceptable on party wall last week.
Cheek is built on the party wall with 4x2 with 100mm kingspan ,18mm OSB. 2 x 9mm sheets of Superlux ,, Felt, Battens and vertical tiles.
She wants 3x2 battens on a D P M fastened to the brickwork with 50mm insulation between forming an air gap. then 50mm insulation over it and 12.5 fireline plasterboard and skim. All this on a 12" solid brick wall with the cheek above.
I was under the impression that the 18mm of "Superlux" was there to stop any fire spreading......It ought to at £136 a sheet !!

Should be warm though with !00 mm of foam insulation.

 

[^woody^]

Superlux" was there to stop any fire spreading......It ought to at £136 a sheet !!

You could have used some MgO board for around £30 each

 

[^woody^]

Thoughts?

The party will needs to be insulated as an external wall

 

[Rnvte]

Thank you all for replies…to clarify my query..the external portion of the party wall (the cheek sitting on the brickwork) is sorted up to render. That portion of the stud is insulated. The rest of the stud wall runs internally, and across the remainder of the bricked party wall and specifically the chimney breast. The gap is c.300mm. The brickwork is sound.
Woody, you seem to indicate following Terrywoolfit's provided advice which is to batten,insulate,fibreboard,skim. Then I insulate interior stud and plasterboard again…correct?
Thanks again.

 

[^woody^]

I don't really understand what you are describing in text. A diagram would be better. But in general, the walls, party wall, roof, dormer checks, whatever, surrounding the new loft need to be insulated to the standard of an external wall or roof.