Metal roof over shingles ?

[junkandcattle]

Been shopping for a new metal roof over for the house with worn shingles. The contractors are offering various methods. First leaving shingles and directly attaching the steel panels . Option two is placing wood battens horizontally with steel on top. Option three is stripping the roof putting down reflective barrier, battens then steel. In Missouri we expect all kinds of weather and the "experts" are leaving me concerned over condensation and ventilation of the metal roof especially if we strip it down first.
Turns out there are two layers of shingles one bidder did not even mention this or other options plus he quoted 29 gauge metal so he is out.

By the way we are looking at Everlast Omni series metal panels if anyone has any experience with this please share.

 

[J king]

Don't put metal over shingles..as the metal expands and contracts everyday it will wear the bottom of metal and rust

 

[junkandcattle]

So the 1" thick wood battens would prevent that ?

 

[Wood'nMetal]

I put a metal roof on my manufactured home about 2 years ago. It had a single layer of comp shingles. At the recommendation of the metal supplier I did 1x4 furring strips right over the top of the 3 tab. Turned out great and I believe made the roof a little quieter in the heavy rains. I do remember they said not to install directly on the shingles because it will abrade the back of the metal.

 

[CNGsaves]

OP . . . . your problem is really the TWO Layers of comp shingles already.

Now adding 3rd layer of metal roof . . . . likely too much weight.

Probably good time to tear all off and start fresh.

Also consider any future plans for Solar - - - - - either PV electric or Solar hot water.

P.S. With roof tear-off, that also gives you chance to improve/fix insulation in attic, soffet vents, easily install bathroom vent fan, wiring work, big OTA antenna in attic, conduit in attic for pulling wiring for DISH antenna, lighting improvements with LED cans in soffet, etc.

 

[rburke65]

Do you really think it's a good idea to apply another roof over 2 layers of shingles that are there?

 

[LB-1911]

Been shopping for a new metal roof over for the house with worn shingles. The contractors are offering various methods.

First leaving shingles and directly attaching the steel panels .

Option two is placing wood battens horizontally with steel on top.

Option three is stripping the roof putting down reflective barrier, battens then steel.

In Missouri we expect all kinds of weather and the "experts" are leaving me concerned over condensation and ventilation of the metal roof especially if we strip it down first.


Turns out there are two layers of shingles one bidder did not even mention this or other options plus he quoted 29 gauge metal so he is out.

By the way we are looking at Everlast Omni series metal panels if anyone has any experience with this please share.

So the 1" thick wood battens would prevent that ?

As previously mentioned - Those two layers need to come off.

Everlast II OMNI / Steel Roofing and Siding Panel
http://munciemetalroofing.com/wp-content/uploads/2015/01/Omni-Series.pdf

 

[Jazz1]

We screw metal right to old shingles on our cabin as we don't play by the rules and never a issue. Also did 7 other cabins and a house same way 20 years ago.

 

[ForceFed70]

With all of those screws in the metal panels, can't see how they could move much. Perhaps with different designs that have a lot less screws and/or use hidden screws and side clamps?

 

[Jess]

As already mentioned, you don't want to install directly on top of the existing roof but with two layers already there, a tear off is in order. That lets you repair any areas of the sheathing, apply a quality underlayment and then install your panels over that. I would suggest that you look into the standing seam type of panels that do not have fasteners through the sheet. Expansion and contraction over the years will require a refastening at some point if exposed. Also, if you have trees nearby, the screws through the sheet catch all the litter and you have to get up there to clean it. Either standing seam or what is called 'snap lock' around here is superior to a roof fastened though the sheet. I have both and regret the shop being sheeting and fastened through the panel.

 

[junkandcattle]

Yes I am definitely leaning towards towards tearing off the shingles for all the reasons already mentioned. As for condensation would it be trapped by the horizontal wood strips?
Also is the reflective underlayment a replacement for 50# paper or do you use both

 

[junkandcattle]

Thanks LB 1911 for improving my post. Appreciate that

 

[slip knot]

I would pull the old roofing off simply because of the additional thickness that the screws would need to go thru. I redid my moms home with standing seem roofing over the old roof and could get longer screws to get the proper penetration in to the decking. but on an exposed fastener roof the factory screws may not be long enough.

I did run 30lb felt between the shingles and the metal.

 

[jd_1138]

As already mentioned, you don't want to install directly on top of the existing roof but with two layers already there, a tear off is in order. That lets you repair any areas of the sheathing, apply a quality underlayment and then install your panels over that. I would suggest that you look into the standing seam type of panels that do not have fasteners through the sheet. Expansion and contraction over the years will require a refastening at some point if exposed. Also, if you have trees nearby, the screws through the sheet catch all the litter and you have to get up there to clean it. Either standing seam or what is called 'snap lock' around here is superior to a roof fastened though the sheet. I have both and regret the shop being sheeting and fastened through the panel.

That makes sense. Seems like the fasteners would have to be caulked so best to not even have them on a roof in the first place.

I'd never install a new roof system over existing shingles. I suspect the contractors who suggested that are just looking for an easier install for them (and probably no cost savings to you).

 

[Commendatore]

Code says no more than two layers of roofing, so definitely plan on removing the shingles. I'm one more vote for standing seam as well. Through fastened panels barely even qualify as a roof IMO.

 

[Gotcha640]

I have no details, but a neighbor has a metal roof that is "isolated" from the wooden roof/shingles/whatever. I have no idea how isolated it is, but you can't hear the rain on it. Very strange.

 

[stimpy]

were I am at they ( codes dept and uses international codes ) will not allow a third layer ( several contractors said panel could be put over the existing 2 ( rather listen to codes enforcement than contractor ) , so we are peeling the roof and doing the new underlayment , also we know of a few soft spots in the plywood from the age of the building ( 36 years old) so that is going to be replaced after the peel .

 

[southalabama]

I'd remove all the shingles and inspect the roof.

But. If not go with wood strips then metal.

I wouldn't screw direct to multiple layers of shingles. I'd like to think my metal screws were solidly into something besides shingles.

 

[matt_i]

I had a house, in the hills of Tennessee, with five (5) layers of roofing on it

And many other homebuilding transgressions to match.

 

[junkandcattle]

Ok Everlast also offers the standing seam roof that claims to be a 24 gauge metal so it will cost more. Off to investigate next week we will see if its in the budget. Sure glad this wont happen before July.

Thanks for all the input

 

[brownbagg]

With all of those screws in the metal panels, can't see how they could move much. Perhaps with different designs that have a lot less screws and/or use hidden screws and side clamps?

oh its moves, I hear mine popping all day as it heats and cools

 

[8mpg]

I think you need to talk to the manufacturer. When I did my roof (rpanel), they said it could go over shingles without a problem. They did not recommend it for standing seam. Exposed fastener roof is just fine to whoever said that the fasteners need to be caulked. They have rubber washers that seal them. As for whoever was worried about condensation with the purlins, you put the purlins at a 45* angle to allow the condensation to run off. Spacing the roof like that can often add the advantage of airflow below. Check out Matt Risinger on youtube. He has lots of great videos about installing metal roofs.

 

[jhelrey]

A rental place by me just did steel roofing. They added the 1x4s and put steel directly on top of that without removing shingles.

 

[James-W]

I don't think anyone is saying you can't put metal roofing over shingles. What they are saying is that putting a metal roof over TWO layers of shingles does not meet code. But even if it did meet code, why would you want to have that much weight on the roof when it isn't necessary?

 

[Catadj78]

My house has metal directly over 1 layer of shingles by the previous owner. The metal roof is now 4 yrs old and I have no problems.

 

[8mpg]

I don't think anyone is saying you can't put metal roofing over shingles. What they are saying is that putting a metal roof over TWO layers of shingles does not meet code. But even if it did meet code, why would you want to have that much weight on the roof when it isn't necessary?

Are you sure thats code where he lives? In Texas I think 3 layers is ok because we dont get a snow load.

 

[csp]

Snow load isn't the only consideration. Think about how much weight a single layer of composition shingles adds.

 

[Norcal]

Leaving a layer, or layers, of existing roof in place is a sign of a bad roofing job, strip it, inspect and repair the sheathing if needed, it will be better roof + remove a lot of weight.

 

[landlord30]

I'd remove all the shingles and inspect the roof.

me too. This is likely the last roof you'll put on this structure. If so, I'd want to rip the shingles off and make sure I had a good deck.

 

[Rookie2]

Just had a contractor look at my house friday. If he strips down to wood then he has a membrane like ice shield to cover the wood , the metal sometimes sweats and will cause leaks he said. He also uses butyl tape on each seam joint.

 

[James-W]

Are you sure that's code where he lives? In Texas I think 3 layers is OK because we don't get a snow load.

I don't have any idea what the local code is for him in Texas, but around here two layers is acceptable, three layers isn't. We don't need a permit nor an inspection to re-roof a building so nobody actually comes around and checks to make sure someone doesn't put on three layers of shingles. In a way I guess you could call it the "honor system" but practically every roofer around here wants to rip off the old shingles even if there is only one layer. You have to insist the roofer go over the top of the old shingles and if you do insist many times the roofer will refuse to do the job. It seems a reputable roofer does not want to give a warranty unless he can do the job right.

When I helped a buddy re-roof his garage he asked the building inspector if he needed a permit and he asked how any layers of shingles is acceptable. That's how I know. But as I said in my last post, even if it were OK to have three layers, why would you want to? What benefit is there to having multiple layers of shingles on the roof? It is just more weight and as shingles age they tend to curl up and the layer of shingles above it won't lay down flat.

 

[Carl_WI]

When I did my barn it had cedar shake and one layer of shingle on it. I used 2x4's every 30 inches up the roof. I used 7 inch screws to get into the rafters. Then installed the steel. It's been through allot of storms and it is still looking great.

 

[Falcon67]

Snow load isn't the only consideration. Think about how much weight a single layer of composition shingles adds.

This. Two layers is going to be around 450 lbs/square. Also insurance. When we moved here, the insurance company would not insure the house until the garage was stripped - it was 3 layers. House was 2. Turned out when we re-roofed in 1999, places on the house had 4~6 layers in places over cedar shakes. With 2x4 rafters. Nuts.

Lots of metal roofs here but I have only seen one installed so I can't help much with the details. If I remember, when they did the house behind us they stripped the shingles and used battens over the decking.

 

[Firebrand]

Get that excessive dead load off your building framework first!

When I installed a metal roof in my house last Fall, I stripped off just one layer plus felt. When the dumpster was weighed in, I discovered I had removed over 2,400 pounds of materials! Just one layer! The metal and new membrane was less than 450 pounds going back on. Do your building a favor and peel off the dead weight before replacing with metal and membrane!

Here in NH, metal is a first choice for roofing over 4 pitch and above, and it's performance is all about the surface it's mounted on. Smooth and clean wins the prize.

 

[TractorJeff]

I've kept quiet as a lot of you guys are probably right! My house has tin/steel over shingles and cedar shakes. I was installed like that in the mid-70's by the owner/retired roofing contractor. Nails are finally starting to work out. They'll be replaced with screws this year if it ever stops raining enough to do it. The attic is ventilated and I have never seen condensation issues. When I roofed my garage/unheated I stripped it and rolled 30# felt, then put the roofing on. Over my shop/slightly heated, the ceiling is insulated so the attic is cold. That roofing was laid on the old boards that had cedar shakes on it. No issues there either!

 

[NUTTSGT]

If it were mine, I'd strip the shingles off and replace the felt or put down a newer synthetic product. Two layers of shingles is a ton (literally) of weight.

 

[maxpower_hd]

I have done a little reading on this a while back because I am thinking about a metal roof myself. One thing I determined was that I would do standing seam. No exposed fasteners.

I read that there are a few different acceptable methods of install. Possibly depending on manufacturer. One is "structural" metal roofing which I believe attaches to the rafters directly without sheathing which isn't an option in my case and probably not yours either. That leaves two that I know of. One is with the strapping and one without. I thought that strapping was typically used when you were going over a single layer of existing roofing. I am removing mine. The other was to use a membrane and attach the metal roofing directly to the sheathing without strapping. The venting comes from the ridge vent and existing or installed soffit vents.

With strapping was described as being louder because you are creating sort of a drum effect. And without strapping was described as similar or only slightly louder than traditional asphalt shingles.

I hadn't finished my research but that was the gist I got from what I have read so far.

 

[cabin fever]

My buddy owns a metal panel manufacturing biz and ive put alot of metal roofs on. My own house has metal. Mine is 2 layers of shingles with 1x4's. One thing i like to do is snap lines and nail the 1x4's directly to the trusses. Some guys will just nail em right to the plywood. I think 1x4's help with air flow under the metal. They also help adjust if your roof has settled and has a dip in it as you can shim the 1x4's. The downside is you need to be a little more careful when walking on it. Its also a little more tricky if you're not replacing gutters but can still be done. Dont buy into the "metal roof is louder" **** either. I can not hear any difference. Most people who claim that have no experience with metal or have heard it in an un insulated pole barn. Just my .02.

 

[cabin fever]

Also i would NOT screw metal directly to shingles. The shingles can scratch the paint on the underneath which voids the warranty. Standing seam is good stuff but probably twice the cost or more. Mine is exposed fastener. The key to exposed fastener is to NOT tighten the screws so it flattens out the rubber washer. The washer will crack and break down over time. Screw it in till the washer just barely starts to flatten. If you have a drill with an adjustable clutch it helps. Again just my .02 from somone who has installed about 30 metal roofs.

 

[8mpg]

For the people worried about the weight issue... metal roofing is very light compared to shingle. I believe most decent shingle is 400-450lb/square. My metal roof was 4600lbs for 43sq of materital. I dont think adding 1lb/sqft is going to make or break a roof.