Metal roof over existing shingle roof

jd4320t

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My girlfriend got a few different quotes for having her roof replaced and one company told her about installing a metal roof over her existing shingle roof. My first reaction was no but some reading and YouTube watching shows it isn’t too uncommon.

I know it’ll show any imperfections in the current roof. That’s what I’m worried about.

Anybody have any first hand experience with this?

Thanks
Doug
 

patience0830

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My girlfriend got a few different quotes for having her roof replaced and one company told her about installing a metal roof over her existing shingle roof. My first reaction was no but some reading and YouTube watching shows it isn’t too uncommon.

I know it’ll show any imperfections in the current roof. That’s what I’m worried about.

Anybody have any first hand experience with this?

Thanks
Doug
If the substrate is solid and you put something between the shingles and the metal it works OK. Fan fold insulation can be used to fill smaller low spots under the metal.
 

decalguy

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We did this on our last house. On the steep two story side we ran 2x4 stringers the length of it and up the ends. Strength and something to stand on while installing the steel. On the flatter single story side we laid tar paper over the shingles and the steel on top of that. We used actual tar paper not the synthetic kind. My cousin said he felt, no pun intended, the tar paper might help slow any possible rusting.
 

Jaybird1980

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I've never seen it put directly on the shingles, but I've seen them grid with 1x or 2x over the shingles and then steel.
 

dudley0

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I always worried about the additional weight of steel over shingle. During final inspection of my place I asked the inspector about it. He said he prefers to see the shingles left on in case there is a leak because of the grommets on the screws.

Makes sense I guess, but that is still a lot of weight to me.
 

VostocK

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I always worried about the additional weight of steel over shingle. During final inspection of my place I asked the inspector about it. He said he prefers to see the shingles left on in case there is a leak because of the grommets on the screws.

Makes sense I guess, but that is still a lot of weight to me.
I never considered the weight aspect. I wonder how much more a metal roof weighs compared to a layer of shingles. There is a house near me that is currently getting a metal roof over the top of what looks to be old shingles with some plastic and a layer of battens between the two.
 

dudley0

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Code won't allow more than two layers of asphalt shingles, but you can put the metal and boards over it no problem.
 

Magyars

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We just plunked a down payment on a metal roof. I had the same concen and he salesman said that one layer of shingles is acceptable.
This is a standing seam roof, not the typical AG metal with exposed screws.
 
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dudley0

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I had a standing seam on my last house. Had a work buddy that used to install them. His words of advice about them was once installed they will either leak or they won't but they will do it forever.

I miss the sound of rain hitting that thing.
 

SnoopLoggyDog

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I want to replace our shingle roof with a metal roof. My beloved wife unit thinks metal only belongs on barns and sheds. Funny because she likes the metal roof on our cabin in Alaska.
 

russc2542

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My house has a metal roof over shingles by the PO. there's a thin insulating layer between them (like thick felt,1/16"???).


Thin gauge sheet metal vs 1/4" layer of tar and coarse sand... sure the whole thing adds up but like shingles, the weight is distributed.

1.4 (+/- depending on manufacturer i'm sure) vs 3-5lb/sq ft according to https://www.metalroofnet.com/metal-...weigh,without compromising the roof structure.
 

CHCRandy

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As a roofer.....I personally would never put metal over shingles, unless homeowner just demanded it. Of course.....I would never lay 2 layers of shingles on a roof unless homeowner demands it and signs waiver. That is like sitting a couple of trucks on your roof structure...then we get a heavy snow and all the sudden the structure is overloaded and supporting 8-10 tons instead of the 5 tons it was engineered to support. Weight is no concern with metal, even the heaviest metal weighs a fraction of a shingle.

You figure a 30 square home, 1 layer has about 3-4 ton of materials on it, now if you double that you have 7-8 tons, now drop 2 feet of heavy wet snow....I have literally seen many homes with broken ridges and rafters from this, the flatter the pitch the greater the risk.

The first thing to consider is how much it costs to tear off a roof. That is the cheapest part, by far...of a roof replacement. On a 30 square roof, you will only save $1200 at most. Now think what you are losing by not spending that $1200. You could have existing leaks and rotted plywood that will never be fixed if old roof is not removed and leak may very well continue and do more damage. Bad flashing that remains bad. You will trap moisture between layers, which will cause metal to rust from the bottom. Another thing to consider is homeowners insurance cost. Many insurance companies raise premiums on metal roofs, especially steep metal roofs....because it is harder for them to access to fight fires.

Don't ever let anyone talk you into putting barn metal on your home unless you just have no choice and have to save money. I know it will work, but ag metal is made for barns unless you specifically ask for coated metal, where the back of panel has a water proofing. You can get ag panels with coating, but you have to order it that way. I would always suggest standing seam with a hidden fastener and always use a 10 or 20 foot synthetic felt, instead of 3 foot wide roofing felt. There are 2 different types of standing seam. There is standing seam that snaps together and then there is standing seam that the snap is bent using a seaming robot machine like this.

 
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