Climate Zone 6-Low pitch insulation questions.

This is a contractor's question posted to an online forum, so it doesn't call for any action from a homeowner. But it's a useful window into how tricky older buildings can be to insulate well, especially if your own house has a low-slope or flat roof.

The post describes a historic brick building in Iowa being remodeled, where the roof slopes from about 4 feet of attic space down to almost none at the back. The old roof had thick spray foam insulation on the deck along with a coating, and the attic below was vented with rotating roof vents and insulated with paper-backed fiberglass between the ceiling joists. Because the building is brick, there's no easy way to vent air out the sides.

The roofing crew plans to strip off the old foam and coating, fix any roof deck damaged by trapped moisture (condensation), and install rigid foam insulation on the outside of the deck rated at R-25, a measure of how well insulation resists heat flow, then cover it with a new waterproof roof membrane. The contractor is now weighing how to insulate the attic space itself to reach R-49 overall, considering options like spray foam versus fiberglass or mineral wool, and is unsure how best to insulate the brick attic walls.

If you own an older brick building or a home with a similarly shallow, hard-to-vent roof, this kind of layered insulation and moisture problem is worth keeping in mind when planning your own roof or attic work.