Thread: Does a metal roof on wood purlins require insualtion next to the metal.

I inspected a house yesterday that was a warehouse turned into a house. It had a metal roof that was screwed to wood purlins spaced about 16" apart +/0. So a lot of the bottom of the metal was exposed. I come from the commercial industry where we had to have condensation blankets on the underside of a metal roof to prevent condensation. The attic in question was insulated at the joist with batts. It had small gable vents and ridge vents w/ sofit vents. Is that acceptable to not have anything directly against the metal with so much exposed? Ty6pically I see metal roofs on plywood not spaced 1x4 purlins.

Originally Posted by ren ramsey

I inspected a house yesterday that was a warehouse turned into a house. It had a metal roof that was screwed to wood purlins spaced about 16" apart +/0. So a lot of the bottom of the metal was exposed. I come from the commercial industry where we had to have condensation blankets on the underside of a metal roof to prevent condensation. The attic in question was insulated at the joist with batts. It had small gable vents and ridge vents w/ sofit vents. Is that acceptable to not have anything directly against the metal with so much exposed? Ty6pically I see metal roofs on plywood not spaced 1x4 purlins.

Ren,

I've almost always seen the insulation on the underside of the metal roofing for commercial buildings because they were open structures (no ceiling below the roof) and that was where they had to put the insulation - no other choice on putting the insulation lower.

On the few structures which did have ceilings below, the insulation was at the ceiling level.

The metal roofing for installation on purlins is "structural" metal panels, the metal roofing for installation on solid decking (plywood/OSB or board sheathing) the insulation has always been at the ceiling (unless they went with the unvented attics with the spray foam insulation on the underside of the roof decking).

I.e., the type of roofing (metal panels, shingles, etc.) was not relevant to where the insulation was placed, it was based on what the structure allowed.