I’m a homeowner in the west Toronto area collecting quotes to redo the flat roof on our 1974 house, and the proposals differ a lot in how they fix the slope. Before I pick one, I want to understand how each option affects the whole assembly, not just the membrane. Photos attached.

Current assembly (inside to outside):

Ceiling drywall

Kraft paper vapour retarder on R20 batts

Ventilated air gap

Roof deck

Torch-down mod-bit. A core test showed the deck is dry, with no insulation above it.

Ventilation:

Intake vents on the sides of the roof.

I suspect some bays dead-end where the flat section meets a sloped roof section

Another section runs into a wall at a different elevation, so those bays may not have a clear path out either

I’m not sure there is any real exhaust, as opposed to intake on one side and nothing on the other.

Problems:

About 800 sq ft across three flat sections.

Ponding in several areas

Scuppers clog constantly with needles, cones and leaves from a big pine next door.

A bathroom…