Metal roof over asphalt shingle

Client wanting to upgrade shingle roof to metal. Wondered about leaving on the shingles. What’s your thoughts?

Thanks in advance.

According to the manufacturer you can do this and save money, but, tearing off a roof isn’t that expensive, you can check for problems before covering with a 50 year roof and why go cheap on such an important area of your home?

I will let them know. What do you think Paul, another $800?

down here in hail country the shingles act as softer underlying surface, thus allowing more noticeable impact dents & damage to the metal than solid decking

also as the metal is installed and surface coating is scratched from granule abrasion it becomes more prone to rusting from the underside…trapped condensation…may not be as bad or a concern in arid climates

Around here tear off, put in dumpster adds about $50 a square.
including cost of dumpster.

3000 SF would add $1200 to $1600

I meet subs who do a roof for $25 off and $25 on per 100 SF.
Also meet subs who get more.

I’m talking Minneapolis/ St Paul area.

You are asking for trouble if you go the route to leave the shingles.

You should not attach metal to asphalt shingles without furring out the roof first.

Metal should not be installed over asphalt as per the Building products University of Firestone. I asked the instructor that specific question and his answer was no do not do it as the expansion and contraction of the metal will scratch the paint and create rust premature

Install radiant barrier, install 1"X4" battens, install metal.

Wouldn’t do that on my house but its common.

“How does a metal roof go over a shingle roof? There are really two ways to install a metal roof over a shingle roof. The first way is to run new underlayment over the existing shingle roof completely covering the old roof. This provides a couple of benefits. The first one being that the new underlayment will act as a second line of defense in case water would to somehow get underneath the metal roof The second benefit would be that it acts as a buffer between the back of the metal roof and the shingle roof. The reason why this is important is because a shingle roof is granulated, very similar to sandpaper. On has the metal expands and contracts due to weather changes, the metal will actually move. Over time if there wasn’t a buffer in between, the shingle granules would wear away at the back of the metal roofing panels.”

I never seen a metal roof go up with out furring it out when installed over asphalt. And I have seen a lot in the last 2 years, many homes along with a multitude of big dairy barns, seems like everyone around is on a metal roof kick lately.

Not furring, but Purlins.

whatcha talkin bout



I was correcting the poster he used furring and my intention was to let him know there were purlins. I can see how you came to that conclusion
Where it comes to metal roof they are called purlins. I’ll change it …Thanks

No, I’m not talking about Perlins when you initially construct the roof, I’m talking about furring strips on top of the existing asphalt shingles. There is a difference.

But you call Them what you want.
Just don’t put words in my mouth! :slight_smile:


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Metal roofs tend to have the least problems in this climate, except for faded paint.

Will let the client know the (correct) options, along with the furring. Thanks everyone :slight_smile:

I’ve installed/repaired 100s of metal roofs over the years and I would never install over shingles, always stripped the roof. I lost a few jobs because of it but after explaining my process my clients understood the importance of doing right the first time. If you going to install a 50-60 year roof, at two or three times the cost of asphalt, why wouldn’t you. Here’s how I did it.

Strip original shingles, repair any sheathing and make sure all sheathing is properly fastened to the rafters.

Install ice and water shield, six feet up eaves and six feet in valleys.

Install 30# felt on rest of roof.

Install Furring strips 24 inches on center, fastened into the rafters.

Install all manufacture’s trim accessories, eave, sidewall flashing ETC.

Install metal panels.

Like any job it’s all about the prep work, installing the panels is the easy part. I always told my clients that if you paying for a lifetime roof it has to be installed properly.

Then it would be battens.

Sure you have…

Sorry Roy, that should have said installed/repaired.

30 years in construction owning my own business specializing in roofing, siding and windows.

Why do you have to be such a dick all the time, you seem like an angry man.

I’m 62 yo this January and have been in construction all my life and and I can smell bull a mile away.
I’m not angry . I just don’t like to be lied to.
I too have put on metal roofing , but not hundreds. However, I have put on hundreds of roofs. Mostly shingles and hot mop.
If we were face to face I’d bet you wouldn’t call me a dick!
But since you drawn first blood I reserve the privlidge to call you a
p u s s y.
We are even now.