Standing seam metal roofing over existing asphalt shingles?

[Diggin It]

I have heard that one big issue is the condensation that forms on the back side of the metal. Personally, I would rather do a complete tear-off, repair any wood, waterproof, then install the metal with ventilation behind it.

I asked about all that when I did mine. Everybody said it wasn't necessary as long as there was enough ventilation under it and that was provided by the 1x4s and ridge cap. Air would flow up from the eave edge behind the 5rib panels and out the ridge cap. Mine has been on for a few years now and I haven't noticed any problems.

My roof deck was in terrible shape. Very old boards, a random mixture of 1x4s, 1x6s and 1x8s, some of which were rotted and cracked to the point they wouldn't hold nails for shingles. The new 1x4s and metal panels just spanned over all of that. Would it pass inspection in a coded area? I have no idea. Part of living out here in the sticks is that we can do what we want without all that trouble.

 

[M5farms]

There is some condensation on back side but it's really not enough to be concerned with. Like I said the separation layer is there for drainage and to keep granules from scratching the metal and causing the metal to rust. Standing seam comes in 3 sizes 12" 14" and 16" as standard. Ask for pencil ribs or wave ribs this will reduce oil canning. 24ga is preferred but 26 ga is suitable for residential. Gonna be over 3.00 a lf .but it is the best metal roof you can install and likely never have to touch again other than cleaning it. 3' wide metal will need fastneners tighten or replaced in 15 to 20 years. I am selling replacement screws now for roofs I sold 15 to 18 years ago. There are no perfect roof systems all have pros and cons , if there was a perfect system I would sell it once and be out of business. If you want to talk in more detail pm me and I will send you my number. I've been in roof distribution for 19 years .

 

[Diggin It]

^^ Do you get into the sectional panels that are stamped to emulate shingles? I've also seen them in stone or brick for walls. A whole lot more expensive from what I've seen though.

 

[IHDiesel73L]

Maybe it's just terminology, but to me, standing seam is the type of metal roof that you don't see the screws and each piece of metal is a foot wide. Because of it's size, you have to install it onto decking. Plywood or OSB. R panels come in 3 foot widths and you can usually span 4 feet with it, so your purlins are installed every four feet. This is more cost effective and fairly common when going over an older roof. Any moisture that develops under the R panels is handled by the existing asphalt shingles. The drawbacks to leaving the shingles in place and putting R panels over it is that moisture the may develop under the metal. It can build up on the Purlins and create mold, and then rot. I've also seen moisture come out from under the metal, onto the porch and people not understand that their roof isn't leaking, it's just a lot of condensation.

If you go with standing seam, you really need to remove all of the shingles and have perfect decking in in place, then covered with felt paper or some other equally approved material. There are a lot of them out there to choose from.

You're right, I am referring to R panels, not standing seam.

 

[M5farms]

^^ Do you get into the sectional panels that are stamped to emulate shingles? I've also seen them in stone or brick for walls. A whole lot more expensive from what I've seen though.

Yes , I have sold alot of them. They are excellent systems but your gonna pay upwards 500.00 a sq just for materials

 

[IHDiesel73L]

Yes , I have sold alot of them. They are excellent systems but your gonna pay upwards 500.00 a sq just for materials

I'm good with a plain old barn style roof and don't mind the exposed screws, etc... It adds character IMO.

 

[Diggin It]

Pricey, yes, but I think there's a misplaced decimal point in there.


At any rate, the 5 rib works well for me, generally under $2/ linear foot, plus screws and trim.

 

[M5farms]

I'm good with a plain old barn style roof and don't mind the exposed screws, etc... It adds character IMO.

Make sure to spend the extra and request ZAC screws .they will protect the washer and you will get long life out of them .

 

[TnAndy]

The barn roofing was simply bought in 12' x 3' sections...

If 3' wide, it's probably not standing seam. All the standing seam I've seen is 16" or so wide per pc. If it went much wider, the hidden screws on the one edge wouldn't be enough to hold the metal down.

3' wide metal goes by the name "Century drain" (among other names), and has rows of exposed metal screws across the panels.


Standing seam makes a much better roof, IMHO, due to the screws not being exposed, but it's more expensive than the 3' wide metal.

 

[M5farms]

Pricey, yes, but I think there's a misplaced decimal point in there.


At any rate, the 5 rib works well for me, generally under $2/ linear foot, plus screws and trim.

No they are around 500 a sq. 3' wide is gonna run around 75.00 a sq just for panels. Galvalume is around 60.00 a sq