Hi all-

I just subscribed here (all access yes!). What I’m posting below I recently posted on another site. I hope the cross-posting isn’t an issue but my question might be a better fit here. I’m also posting in general since I’m still learning and I’m going to have a lot of general questions over the course of this project. 

I have a brick detached garage–about 18×16 interior dimensions–built around 1937. It’s unfinished and I’d like to finish it so I can use it as a more comfortable workspace for projects. It has a gabled hip roof with the original slate roof. Baltimore, zone 4.

My question has to do with framing the walls and strengthening the roof so I can store odds and ends above (few hundred pounds at most). I’m considering using either (1) a system like insofast on the walls with an additional 1 or 1.5 inches of rigid foam for the walls/framing OR (2) conventional 2×4 stud framing 16″ oc. I’m aiming for at least R15 on the walls.

If I go with the more conventional stud framing, I’d use about an inch of CI rigid foam directly to the brick walls, then 2×4 studs attached to the concrete slab and at the top plate(?), with mineral wool or something similar in between the studs. I only have about 5.25″ between the brick and the garage door rails.

I have tons of questions, but for the sake of the post I’ll stick to one-ish question related to stud framing. What I’ve seen online is that the top plate of the studs attaches to the joists, but I don’t have joists in my garage. I have 3 rafter ties (2×6 actual) going width-wise and two rafter ties above those going front to back. On top of the brick wall are 2 pieces of wood, which I assume are serving as the top plate for the brick, and the rafters connect to them. They look like 2x8s each. One is slightly higher than the other. The wood plates connect to the brick by a variety of fixtures.  For completeness sake, the rafters are 2×6 actual with the hip rafters being 2×8 actual.

I created a Google album here (hope this is allowed): https://photos.app.goo.gl/4CFW2NoWK5opd42W8 

As I said, I want to be able to store some things above on the rafter ties, and I need a connection point for the top plate of the stud walls. I haven’t been able to find information that’s directly on point, but what I’ve read so far suggests that maybe I need to install more rafter ties–maybe 2×8 (16 or 24″ oc) since modern 2x6s will be smaller than what’s in there now?

I’m still not sure how the top plate of the 2×4 studs would connect to these new rafter ties. I haven’t been able to find good videos showing top plates of wood framing on a brick structure. I see certain metal ties that could be used to connect the stud double top plate to rafter ties. Maybe there’s a way to tie the stud plate into the wood plates on top of the brick? They are recessed, plus with the foam before the 2x4s I’d need something to span the distance.

I’m a visual person and I struggle with the technical terms, so if anyone responds–if you have pics or videos you can point me to that would be great.

One other note, I’ll insulate the roof as well but I’d like to avoid the weight of drywall or plywood sheathing so if I can leave the top layer of insulation exposed that would be preferable (was thinking rockwool comfort board). I mention that as the weight I add to the roof will most certainly factor into things here.  Thanks!

Matt