Exposed Fastener Metal Roof installed over existing shingles

Hi i have a 60 square home and extra garage combined. This is a well built 42 yr. old home with 2 layers of shingles in pretty good shape can I some how put metal over the exiting shingles? I had some wind damage and have some ins. money

James, due to the low weight of metal, it would not be unusual for a metal roof to be installed over two layers. However, if you're in an area where a building code is in effect, you likely will not be able to install a third layer of roofing. If that is not an issue where you live, I'd suggest checking with individual manufacturers of products you like. Aluminum would be a lower weight option than even steel.

I have a stereotypical farm barn built around 1900 (40 ft x 80 ft) in southern Wisconsin that has what appears to be two layers of asphalt shingles on it, possibly one layer of cedar shakes, and then 10"-12" boards on top of rafter framing. I am going to install metal roofing sheets. I store quite a few bales of hay in the mow every year (4000 small bales), and have only a few hobby farm type animals (i.e couple pigs, chickens, ducks, 2 two horses) in the lowest level. The walls of the barn are wood, with plenty of gaps between the boards which promotes air-flow which is essential with fresh hay storage. I plan to have a contractor install the roofing. He has done many metal roofs, and intends to screw 2x4's on top of the existing asphalt shingles, making sure to hit the rafters. Then he will screw the metal down to the 2x4's. My questions....Should I be concerned about condensation in this instance? He had never installed a membrane on previous roofs unless he did a tear-off (is what I was told). Also, I plan to use a medium/dark gray tin color. Should I have a heightened level of concern with condensation due to the darker roof color? Most barns in my area have white metal roofs, with a few green. I have seen a couple gray, which I found to be appealing. Finally, I asked my contractor about installing a roll-out ridge vent (typical on residential structures) across the entire ridge of the barn to allow some of that heat to escape (especially in the summer months). He said that he had never done that before, but doesn't have a reason why he couldn't. What are your thoughts?

If the space isn't heated or cooled, you should be fine. Sounds like there is plenty of air circulation and if you didn't have an issue before, you shouldn't now.