How to - insulate and air seal this….

[BadgerBodger]

Thoughts on a postcard…

 

I have a number of concepts which I’m sure will work but looking for fresh takes on how to take airtight AVCL line from door frame to Iinternal insulation (inner face) - gap circa 415 to traverse but only 20mm or so to work with…. 
 

Current lines of thought are to AVCL to frame behind build-up and use jacko/marmox board to form reveal with stop end bead to frame to restrain the board. 
 

Seems like a lot of work though. So if anyone has a cleaner solution from experience it’s welcome. 
 

Maybe the more slight frames were a bad choice. doesn’t leave much to work with. 

Problem occurs 13x to varying degrees albeit this is one of the tighter ones 

 

Edited yesterday at 15:51 by BadgerBodger
Clarification

[Iceverge]

That's very tight to get insulation in there but anything would be a great improvement to prevent condensation etc.

 

How many mm do you have to play with, it looks to be only about 15mm? 

 

I would get Marmox board and shim it level and screw it to the brick reveal, holding it back 5mm from the window frame. Squirt behind it with FM330 or other low expansion, airtight expanding foam. Then use a white acoustic/airtight sealant to seal the 5mm gap between the marmox and the window frame. 

 

The room side of the Marmox can be taped to the PIR. 

 

3MM Gypsum skim over the marmox then. 

 

Consider adding some kind of check strap or other stopper to the window sash to stop it hitting the reveal and cracking it afterwards.

[BadgerBodger]

Nice. Looks like I was half way there. 
 

Yeah, it’s deceptive but could be at little as 15mm so I was thinking 12 mm marmox and skim. 
 

Was hoping to avoid shimming though 🤣

[Iceverge]

That lead to yet another amusing and informative visit to urbandictionary.com

[Nickfromwales]

On 27/08/2026 at 17:58, BadgerBodger said:

Nice. Looks like I was half way there. 
 

Yeah, it’s deceptive but could be at little as 15mm so I was thinking 12 mm marmox and skim. 
 

Was hoping to avoid shimming though 🤣

Just dot & dab them on, using flexible, extended set tile adhesive, as I did for a previous similar project. Forget shims / screws, you'll be there forever trying to get all those reveals and heads plumb / level / square etc.