Timber framed (with dwarf wall) garage conversion - Insulation

[umpljazz]

I'm looking to convert half my garage into a 'habitable' room so will need to meet the regs for insulation. Looking elsewhere here, I can see the following layers are suggested...

From the outside in:

Cladding
25x50mm battens
building paper
9mm wbp ply
100mm studwork
100mm full fill insulation
vapour barrier
Internal finish

Currently however the walls consists of just...

Cladding
100mm studwork
Internal finish (ply)

Given the difference, it's looking like I'll need to remove the existing external cladding to add the building paper and ply.

My question is how best to handle the dwarf wall (roughly 6 courses above dpm) that the existing timber frame sits on, so that the resulting interior finish is flush across both parts? It's currenty a solid wall of 2 bricks thickness (with no cavity), so will require some form of insulating.

 

[noseall]

You will need to include a further 50mm of insulation across the studs internally in order to bring it up to standard. With this in mind you could allow the additional 50mm insulation to travel all the way to the floor. You could either squirt fixing foam behind the insulation first or use dab, depending upon how you chose to insulate. Both methods would require a supplementary mechanical fix in any case.

Also, use breather membrane instead of building paper.

Edit: Just read solid 9" wall. A similar method of insulating as above can be used externally depending upon how the timber framing is located on the dwarf wall.