Metal roof over asphalt shingle

Okay so between the 2 of you Roy and Peter tell me then have all the 100’s of metal roofs I’ve seen go up in the last 2 years been installed incorrectly just based on being laid over asphalt (all have had battens) or (furring strips). Don’t make this question more then what it is as I said just based on over the asphalt with furring, battens. And why give me a reason why not yes or no.

Kenny, the number one reason is what are you securing the furring strips to? How do you know if the attachment, whether screws or nails, are secure. Most of the roofs I’ve repaired over the years were failing because the panels were not attached or have come loose. I’ve seen metal roofs screwed through three layers of asphalt and the entire roof was buckling. I think most manufactures allow this method but I always chose to strip the roof and start over, that way you know the furring strips are nailed into rafters and there is a solid substrate to screw the panels to.
Hope this helps and of course this is just my experience but we have some pretty harsh weather in my area between the heat of the summer and snow and ice in the winter, lot of expansion and contraction.

Thanks Peter so the main reason is just to make sure of the sheathing and what the furring or battens are screwed to. Have thought of that my self when watching so many going up over the asphalt but never have installed or worked with metal roofs. Thanks have a good one:D

You nailed it Peter and I had a Client take a company to court for the very same reason.

Your welcome Kenny, Here’s the result of what I was talking about.

This roof is less than ten years old and is buckling across the entire field. Note in the last picture the screws in an attempt to secure the panels back in place.

Like I said, the manufacture’s may allow it but in my area it’s not a good idea.

May look good at first but wont last long.

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I personally have installed a permitted metal (aluminum) cap overlay over existing comp shingles on few occasions. Installation requires removal of shingles around outer perimeter down to sheeting. All vent flashing and pipe (except plumbing vents) are removed. Next the outer perimeter, valleys, ridges and around vents are then framed with 2x4’s, then 4’x8’ sheets of foam insulation (2” thick) are added length wise starting along the bottom edge. Now additional 2x4’s are added against foam insulation. This process is repeated all the way to ridge, while cutting foam to fit. Next the metal roofing is then installed and attached over the foam and 2x4 framing with either a drip edge or gutter along lower outer fascia. New flashing and or vents are installed as needed.

But first always check with your state, county or city requirements, I’m sure they’ll defer.

So Gary are you saying the 2x4s are on top of the foam

Thanks Peter, its really something to learn as we have not had many metal roofs here and now with so many going up we might see something like this in the future and this will all be help to understand why.

No, the 2” thick foam is put between the 2x4 framing. Since the foam is 2” and the 2x4’s are 1 1/2”, when the metal is applied over and attached to the 2x4’s this helps with a tight fit, since the foam has a little give.

Thanks Gary that’s what I thought you meant, just maken sure

Agreed. Slow abrasion.