Is it OK to install metal roofing over asphalt singles? There is only one layer of shingles. Thanks.
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AFAIK, Metal roofing comes at a significant price premium to shingles... you pay for their longevity.
I'm not sure why you would want to mess with putting a superiour product over an inferior one, when that inferior one might impact the installation of the other.
I'd be inclined to rip them off. It goes very quickly and will let you inspect the substrate for rot and other defects.
I've seen it done many times -- on old, falling-down barns and sheds out in the country. Even a few cases of metal over wood shingles.
Ugly as sin, won't sit flat, won't last as long.
prout,
We have done many of these but we strip the roof with 2x4 first. 2x is shot and screwed trying to hit the rafters as much as possible.
We even take out any sags if we can't do it from the attic.
KK
Laying metal directly over shingles is a bad idea. The metal will move some from expansion and contraction and can rub the finish off of the back from grating against the shingle aggregate.
The typical solution to this is to lay a grid of 1X over the shingles and furring the grid straight. But this makes the eaves and rakes taller and can ruin the appearance of the structure and adds cost to the installation and makes future walking access a little tricky.
Tearing off the shingles allows for inspection of the roof deck at which time any rotten sheathing can be addressed. Also, it's tough to find any future leaks you might have since water that gets by the metal can run for a while on the shingles 'til it finds a hole.
Leaving the shingles on is false economy, IMHO.
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