Asphalt to Metal Roof

[Neil Gaskin]

The real issue really becomes how well you fasten through the existing roof into the structural members of the roof framing. Gravity mart have a very small part to play in that but you're talking about uplift which has little to do with the weight of the return and a whole lot more to do with the connection of the roof framing be at stick or truss to the top plates of the walls.

I would argue no roof has ever been created with the sole intention of overlaying an existing roof.

You can also get into warranty issues by laying over.

But it is cheaper and easier so lots of folks do it.

To be fair there are probably a small percentage of issues that are caused by laying over. But if you're talking about spending close to $100,000 what's a few more to do it right

[Malcolm Schweizer]

I have a good ol' corrugated metal roof that has quite a few patches and is in need of replacing, but it withstood direct hits from Irma and Maria, with 180+mph gusts in Irma, and 150+ sustained! The only damage I had to the roof was one very small leak where a 2x4 from my neighbor's house hit the roof. The side of my house has tons of 2x4 shaped marks on it. The neighbor had erected 2x4 scaffolding prior to the storms in order to do work on his house. He was out of town when the storm hit and didn't take it down. It pummeled my house.

So- I would go with either standing seam or corrugated metal roofing. They make a very thick aluminum one that I have heard good things about and it lasts forever. The other option is galvalum that is metal with a galvanized/aluminized coating. It is supposed to last 20 years in salty conditions.

l wouldn't see a problem with putting it right over the shingles, except remember that you are adding weight to the roof. Make sure it can take that much weight, which probably won't be too much for metal roofing. If you get hit by a hurricane, you have shingles up under your panels, so even if some panels blow off you have a second layer!

As for the ones that look like tiles, my friend has that on his roof... or he HAD that on his roof. He lost a number of the tiles during the storm. They have a lot of windage, and they seem to me to be less sturdy than just corrugated or standing seam.

[Jerome Stanek]

I am in the process of getting quotes for metal roofs and the exposed fastener is about half the cost of the standing seam. The material I am leaning for is a premium metal that looks like standing seam

[Mark Bolton]

I can only give you my personal experience from 30+ years as a GC, have always been an asphalt guy, but we did a LOT of metal....

First, its done here locally all the time but we have never, nor will we ever, install ANY metal roofing over an existing shingle roof. The issues are numerous. Even with underlayment, metal moves. The sun hits it, it expands, sun goes down, it cools. This works fasteners beyond belief when they are perhaps 1/2" (thickness of the shingle bed) off the substrate. Second, the installer has no idea whether their run of screws is landing on the high of a shingle course or the low. If their run (we pre-drill all our sheets on the ground) happens to land in a shingle valley, you are relying on the strength of the metal to compress the sealing washer. Through time, you will without a doubt have leaks behind these washers that will cause the screws to pull out. You may not see the leak internally because the installer relies on the fact that you have a roof below their roof. But it will happen guaranteed. Third, the vast majority of installers that will fly a metal roof over shingles do NO RE-FLASHING whatsoever. They rely on the existing step flashing, side wall flashing, they install NO pitch breaks and simply nest classic rib over top of the lower course (you have about 1/4" of protection from the weather), they install NO BUTYL tape under ANY of their trim (all corners, ridge, side wall, end wall, etc. is to be installed with butyl tape between the trim and the roof sheet), they do NOTHING but caulk roof penetrations, chimneys, turbine vents, all are left with only caulk as their protection. There is NO caulk on a metal roof we install other than for a counter flashing. None of the installers in our area do any of that detailing. They dont close the profile ends (we fold all our ridge and corners CLOSED, so there is no opportunity for wind, weather, or bug, infiltration).

With regards to standing seam or tile, as has been stated, most now are buying standing seam pans and using a blind clip and the subsequent panel simply laps over the clip and the initial panels seam. This option in our area is about double the cost for material and slightly less than double on the labor. True standing seam involves the installer running a motorized roll crimper up every seam that literally crimps the two panels together. This would be in the high range of your estimate in my opinion.

In the end, I would never allow someone to install a metal roof over shingles in any home I intended to be in for more than perhaps 5-10 years regardless of classic rib, pre-manufactured standing seam, or tru standing seam (a true standing seam guy will not off that option anyway).

I would ask the installer specifically if they install ALL NEW side wall flashing, end wall flashing, closures, and the like.

If your even considering classic rib (doesnt sound like it) you need make sure your installer installs as already mentioned, they must stitch every lap, they must stitch up both sides of the lap, they must pre-drill all panels, they must install fasteners to the manufacturers spec's for your area. Otherwise your warranty is void on the material. Mind you the warranty from most any manufacturer will only cover material replacement. NO LABOR.

Last, if you opt for rolled material over tiles be very careful about length. Many installers will run the longest lengths they can to speed the job. Again, metal expands A LOT. There was a commercial job here where the installer had a portable roll former come in on a trailer and they ran very long material and the minute the sun hit the sheets they sheared screw heads off like popping the heads off a dandelion.

As I said, Ive been a shingle guy for 30 years but in hurricane territory Id be looking for a different roof material.

Just my $0.02

[Jerome Stanek]

When I had my quotes they are removing the shingles and installing new flashing along with ice guard along the edges and in the valleys. They gave me a choice of metal and paint options. The company I am leaning for also figured the job on site and was on time when he came. Not a big company but he gave me several people that they have done business for and also let me know where I can see their crew working on the kind of roof I want.

[Jerome Stanek]

Just figured it up and 3 different roofers all came in at about $3.25 a square foot

[Mark Bolton]

Just make sure they all do the flashing details. And if there are any overlay flashings you have to make sure.. butyl tape, butyl tape, butyl tape. At least around here no one uses it. When we ordered roofs and ordered butyl tape, our suppliers would laugh at us.