Carl, I am in the planning stages of new construction. I was thinking about having a Galvalume® metal roof with furring strips, creating an air pocket for hot air to rise up to ridge vents. This also can act as a radiant barrier.
I was talking to a contractor and he stated if I used closed cell spray foam insulation on the underside of the roof decking, it wouldn't have any increase in energy efficiency.
He recommended just using composition shingles and saving money. Is this true?
Hi John, You have two separate issues here.
You obviously like metal roofs. So do I!
1. The benefits of metal roofs are numerous and I feel that they make the best looking roofs for certain homes. If you want the look of a metal roof, as well as the other benefits, that should be your main deciding factor.
2. Closed cell spray insulation applied to the underside of the roof (decking) has its’ own set of pluses and minuses. The biggest negative factor is that by sealing the bottom side of the roof decking, attic air that would normally cool asphalt shingles (as well as metal panels) from below is not there. This could cause an early failure of the asphalt shingles and possibly void their warranty.
Also, by sealing off the attic (no ventilation) with closed cell foam insulation, moisture can build up in the attic as well as between the asphalt shingles and the foam insulation.
Read my page, Roof & Attic Ventilation is Important
Courtesy Central States Manufacturing, Inc.
In my opinion, your idea is excellent. Good venting via ridge venting makes for a longer life for the roof, attic framing members, helps prevent “ice damns” in cold climates, and cooler temps in hot climates.
As for cost, Metal Roofs have one of the lowest, if not the lowest life cycle costs…plus, you get a darn good looking roof.
Carl Heldmann, byoh.com