I’m an electrician by trade but am in the middle of a remodel and addition of a house in southern Ontario that we intend to live in with our family of 4.

I will lay it all out for you and then ask a couple questions. I have done tons of reading but am having trouble deciding on a few things.  The forum’s wealth of knowledge and experience would be greatly appreciated!

We are talking about a 2 Story house with block wall foundation and poured concrete floor in the basement. 2×10 4 ply laminated beam for main floor with 2×10 joists. 4” tongue and groove sub floor on the main floor.

2nd story is 2×8 joists with old crate planks (mostly 3/4”) for a subfloor that will definitely be replaced!

The roof is 2×4 rafters with collar ties and a knee wall. The upper floor overhangs the house 21” on all sides. So that’s the roof overhanging on the sides and the floor joists overhang front and back.

Outer walls are 2×4 framing with mostly 12” wide plank sheathing. Currently has vinyl siding which is to be replaced.

Addition is to be a 20×24’ garage with bedroom above.

The biggest things I’m struggling with is exterior wall assembly. Initially I was planning for closed cell spray foam 3”. A new wrb on exterior, then exterior insulation and a vented rain screen. Likely with a cement board style horizontal siding. It has come to my attention that exterior insulation with cc spray foam is a no no because it can’t dry inward due to the spray foam. What are people suggestions? I’d prefer not to lose more room on the interior otherwise flash and batt would work well I think. Also, am I better with peel and stick wrb or not? I’m concerned with the peel and stick sticking to the old planks with so many seams.   It would provide a good air barrier though. What are your thoughts on header hangers to save on wood around windows and add more insulation?

Second biggest problem is leveling the main floor. It varies up to 1 1/4”. The 2×10 joists are attached to the beam with a square cut out and sitting on 2×4. It seems as though they are sagging at the attachment point. The only thing I can come up with is to detach each joist, sister a small piece and reattach it to the beam with a double joist hanger. Thoughts?  If I go this route how long would the sistered pieces need to be? There are a few spots on the subfloor to patch and I was thinking about attaching new subfloor sheathing over the existing after the patches are in. Do you think that’s a good idea? If so should I screw to the old subfloor or to the joists below. The intention is to have engineered hardwood flooring.

Next, the sloped ceilings on the 2nd floor. I intend to strap an extra 2” on the existing 2×4 giving a 6” cavity for cc spray foam. The roof sheathing is 12” wide 3/4“ thick planks. Is there anything to watch out for or is there a better way to insulate? Where the slope meets the outer walls it overhangs. Is it better to spray the overhang and soffit or put up a backer board flush to the sheathing and essentially extend the wall to the sloped ceiling and then spray foam?  Any other ideas?

Last, the house has a 5 year old gas furnace that is capable of heating the whole house.  I am concerned with its ability to condition the space above the garage.  It is 20×24 master bedroom with a walk in closet and master bath. I would love to put in a VRF heat pump\AC that could do the whole house and use the current furnace as an air handler and backup for extra cold times but i don’t think that’s in the budget.  Currently i think the best plan is to use the furnace as is and if needed add a mini split to the room above the garage.   Any concerns jump out to people?  I will either run ducts to the garage bedroom under the joists and spray foam the underside of them therefore keeping them in the conditioned space or use floor trusses and run them through that.

Any and all help would be much appreciated!!  I have attached some pictures in order to make things more clear  let me know if you need to see something else!

Thanks so much in advance!