I think this is the right place to ask as this is about constr tech and insulation so here goes…

Question about my 850 sq/ft cottage/home (currently used as a 10 day/month cottage year round) heated with oil.
Located in Kenora, Ontario, Canada P9N0E7. It sits on a concrete pony wall (poured directly on granite) with a 2×6 wall averaging 4.5 ft (all conditioned and insulated) for a basement crawlspace.

Standard early-90’s 2×6 home construction, no exterior foam, tri-pane windows and a double pane sliding door to east side deck.

The design is simple, a 5/12 (gable) roof covers the home, the ridge line runs North/South. its roughly 30 x 27.

The east side has two rooms; the MBR (at the south end) and the living room .

Both of these rooms have a sloped ceiling. I can see the pitch is the same on the inside as the exterior so its probably (I don’t know for sure and don’t know how to find out) a vented 2 x 10 or maybe 2 x 12 sandwich with this lay up (which is typical around here)…

interlocking 1 x 6 cedar
5/8 drywall
vapor barrier (6 mil poly was standard and is visible on exterior wall openings)
fiberglass batts to fill the roof bays; maybe leaving a gap at the top for ventilation (but maybe not)
7/16 or maybe 1/2 plywood on roof deck covered by a single layer of very tired asphalt shingles.

the west side of the house has (from S to N) kitchen, bath, 2nd bedroom, all under a standard 8′ flat ceiling.

I have been in the attic (south side of house has a gable door which allows access to flat roof) I can see one layer of R20 then R12 fiberglass insulation here.

My plan is to blow cellulose on top of the fiberglass to a total of about R60.

Since the shingles are coming off this spring I would appreciate some ideas on how to increase the insulation on the east side of the house (the sloped roof).

I considered adding 1″ or 2″ of rigid foam to the exterior roof deck then recover with OSB or plywood but wonder if that is smart since I don’t know the roof stack up on the east side.

Also, if the roof deck gets 2 and 1/2 inches taller on the east side how does one mate with the new vertical gap at the ridge line; I assume there is no point in adding foam to the exterior of the west side since that is a flat insulated ceiling.

It occurred to me that adding the foam to the interior might work! Any thoughts?

The reason this was discarded as a possibility is the ceiling is finished with interlocking cedar boards and to lose that would be a tragedy. Besides the roof deck is bare when shingeling so that seems like a better place to put it….if it works there.

THANKS 🙂