Angled walls

[blue96bird]

I am in Cleveland, Ohio and the second floor of my house has full ceilings in all of the bedrooms and bath but there are walk-in closets that line the sides. These closets have a 96" inner wall and an outer wall that is comprised of a 57" lower wall and a 50" upper angled wall. I have blown-in cellulose in the 57" lower walls and there is the equivalent of R-38 in the second floor ceilings/attic floor. There is no insulation whatsoever in the 50" upper angled walls. Therefore, this time of year the closets are freezing cold.

The reason that I have not yet addressed this is because I am unsure if and how these upper angled walls should be vented. There are no soffit vents and I don't see any practical way to vent them because there is no overhang at the edge of the roofline. The inside surface is finished (wood lathe/plaster) and the roof is 1x planks with a couple of layers of asphalt shingles on top.

Can I insulate either with spray foam (closed cell or open?) and disregard venting? Or, should I install baffles against the roof surface and slide batts between the baffles and wood lathe? Either should be reasonably possible without any demo because I can see right down the cavity to the gutter line from up in the attic.

[pushkins]

I doubt you'll be able to successfully slide batted insulation down the void especially with lathe, all it takes is a simple nail or splinter to catch the insulation and it will start bundling back on itself leaving a void.
IMO the spray foam would be a more successful option.
To baffle or not with the use of spray foam is still a sketchy question and there are plenty of arguments on both sides of the question. Building inspectors can have their own preference as well.
As you have no soffit venting allowing airflow through this area (or any soffit to install one in in the future) I would think that the spray foam from lathe to sheathing would be the best option.

[clofembece]

You dont want to sandwich the insulation between 2 layers of poly, any moisture in there will be trapped in there. Id do the cold walls for sure, the shared warm walls to your neighbours.. Id only poly your side if their side of the insulation isnt polyd.