Can I insulate this roof from the inside without foam and rot? 1896 brick house, box gutters, hipped roof (Zone 5)

A homeowner renovating an 1896 brick house near Pittsburgh asked for advice on insulating a tricky roof without spray foam. The house has a hipped roof with plank sheathing, shallow rafters, and built-in box gutters sitting over the brick on lookouts. Since the roof itself isn't being replaced, any insulation work has to be done from inside the attic space, which rules out some common fixes. The owner originally planned to insulate the knee walls (the short vertical walls that separate attic space from living space) but is now considering bringing the insulated boundary out to the brick itself, using mineral wool board paired with a smart vapor barrier membrane.

The sticking point is venting. Normally, roofs like this need a path for outside air to flow from soffit to ridge to keep moisture from building up in the sheathing. But here, the box gutters block that airflow at the eaves, and the hipped shape cuts off many of the rafter bays anyway. That raises the question of whether an unvented roof assembly using mineral wool and a smart membrane, instead of foam, can safely manage moisture in this climate without risking rot in the old wood sheathing. The owner also wants guidance on detailing the transition where the brick wall meets the roof.

This is a case study in a tricky, older-house retrofit problem rather than a program announcement, so there's no rebate or deadline involved. If you have a similar old masonry house with a roof that can't be vented conventionally, this discussion is a reminder that insulating from the inside raises real moisture questions worth working through carefully before committing to a method.