Metal Roofs?

1) you can leave the shingles on but be sure the new metal roof on top of it doesn't exceed your roof loading design. it tried to roof over the shingles on my barn (3 layers) but the sheathing was too far gone so we had to strip it.

2) it absolutely has to be put on a purlin system. 2 reasons: the constant movement of the building will cause the shingles to abrade through the metal if in direct contact and the condensation on the underside of the metal roof ha s to be allowed to drain freely.

3) don't insulate gaps...see drainage above

4) see above.

just a note...if you get large hail it will punch right through a metal roof. a client of mine (i work at a building engineering company) in minnesota is putting a very thick shingle on his new roof (forget the name) as it's the only product they've found out there that bounces the hail off without damaging the roof

I hired a local contractor to do mine and I think they did a fine job. They furred over the single layer of shingles and screwed everything down. My house is 28x48...the roof will be a tad longer/wider...anyway, it cost me $3300 installed. I wouldn't worry about hail punching holes in it....if that ever happens, call the insurance company again!

Around here shingle roofs take a pounding. Metal roofs seem to hold up just fine. Another bonus is metal roofs reflect sun a little better, and don't hold the heat like composition roofs. On the Habitat for Humanity houses I've worked on, we used 5V galv roofing screwed into 2x4 purlins, and radiant barrier material under that. In the years we've done it that way we haven't had any problems. I think they're a bit easier for the unskilled, i.e. volunteers, to install. Harder to walk on though; I've nearly slid off a couple!

c.