Todd Miller - Roofing Expert

New Metal Roof

Question from Al in Texas:
I’ve got a few questions for you regarding metal roof installs.

We’ve currently got a composition shingle roof that is 8 years old. I has some hail damage, but no leak problem at all.

There is a local job we looked at that uses U panel on a new construction, and are giving some thought to it. Also the 5V Crimp and AP.

The U channel has been recommended as an install OVER the existing shingles, without new underlayment. I have seen you recommend new barriers. What do you think of an install of this over our exisiting shingle? Also what type of lattice grid or straight 1×4 or 2×2 type thing would you consider putting over the existing shingle to make it lay better? We have an “architectural type” shingle at this time and it doesn’t lay as flat as some of the others.

I’m leaning toward a complete tear off…If I do, would you recommend any lattice grid on a new install? I’ve thought it may circulate the air better, but in a hail prone area, if does not lay flat, then I think there is more chance of getting dents…

Any comments or suggestions would be appreciated.

My Response:
For several reasons, I always suggest new underlayment beneath metal roofing, even if it is being installed over old shingles. First of all, I interpret the International Building Code as requiring it. Second, I would be concerned about abrasion between the old shingles and the back of the metal. And, third, it is a good extra safeguard to ensure long term performance of the roof system.

If you want to use a gridwork, you must use what the roofing manufacturer suggests using, and it must be spaced accordingly with appropriate fasteners.

If you use vertical battens and then horizontal you can vertically ventilate the resulting chamber for extra energy efficiency.

I would also encourage using a product that has reflective pigment in the paint, for a cooler attic.