Dormer construction detail advice, please

[Tony L]

Here's an update of my diagram showing the dormer plan on top of the foundation plan (just so we can see how it all lines up).  Any comments on this (positive & negative) will be gratefully received.

 

Are there any colour conventions I’m flouting as I draw my diagrams (eg airtight layer is always shown in red) or does everybody just choose any colour they fancy as they make each drawing?  I’m using MS paint, & I can’t figure out how to get the neat S shaped squiggles that usually represent insulation.

[Russell griffiths]

Why build that wall solid, build it in a cavity to the same spec as the outer walls and continue it up past the roof line. 
I’ve got two large internal walls that pop up and suddenly become external walls, it was easier to use the same build method all around than swapping to a different build method for just 1.5m of wall poking up. 

[Tony L]

I don't think that's an option now.  For reasons I won't trouble you with (as there are so many), the B&B floor is already built, with the 215mm sleeper wall beneath.

 

Also, I wouldn't really want to waste space with a cavity wall inside the house when I'm sure there will be a solution based on a 100mm wide block wall.

[Russell griffiths]

Got to be timber then, insulation in the studs, some on the inside to bring it out to the right dimensions you need. 

[Tony L]

Thanks, @Russell griffiths. 

 

My understanding now is: I should build almost all of the dormer by continuing the ground floor cavity wall up to the flat roof on top of the dormer, as suggested by @ETC .

 

I made a mistake with my mark ups on the previous Sketchup & there’s a new one below showing the section that will be in timber, behind the diagonal orange lines.  I’m thinking the problem with lateral loads is now solved, because the outer edge of the timber section can be built off the pitched roof rafter, like a normal dormer.

 

The cavity will be closed off with a cavity closer, where the blue line is. My problem now is, how do I attach my first studs to the ends of the 100mm wide blocks on either side of the cavity, where the blue line is.  I don’t think I should be drilling into the ends of the blocks, in the same way you could drill into the face of a block wall.  Perhaps I should use L-shaped brackets fixing into the centres of the full block faces.

 

& should I put frame sealant on the ends of the blocks before offering up the timber stud or is there a better product to get these to fix together well & allow for the timber to expand & contract?  Perhaps this is not worth worrying about so long as I get my airtightness detail right across the masonry-timber junction.  Any thoughts on the above would be most welcome.