# metal roofing over shingles



## Brian Peters (Feb 2, 2011)

I am working on pricing a re-roof job, a metal roof over shingles. I have done several of these in the past, some of them we tore the old shingles off and started over, others we screwed 1x4's to the roof over the shingles. I have always wondered about the 1x4 method, seems condensation could potentially rot out the 1x4's. 
There is just one layer of shingles so weight is not an issue, and there are a lot of these metal roofs put on around here and most are done the way I just said. 
Just wondered what y'all think, maybe there's a better method. I'm here to learn, I don't like to be one of these guys that does it one way "just because that's how everyone does it around here "


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## Randy Bush (Mar 7, 2011)

Brian, Roofs are done both ways around here. I have pretty much done tear offs then put metal on . I am not sure what to think about the 1x4s yet. Seems to me if you have good sheeting down and roof is screwed off right way it it needed. Have done a couple with just metal over the shingles. they seem to be holding up well with no problems. Have a big job comming up , a church roof like 60 sq that we are thinking of just putting it over the shingles. They are laying down really good now and am thing of using the 5/16 wood screws on it . Also at the bottom edge I like to screw on both sides of the rib so the panel is held down good . I kind of wonder about the 1xs and water too, plus I think it is better for the panels to be on a flatter surface.


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## Red Adobe (Jul 26, 2008)

direct lay: you'd want to paper over the shingles so they dont rub......and theres always a chance of running a screw into a soft spot or joint and it not holding or setting the washer and leaking. This has happened alot around here and is very hard to fix once the roof deck is rotted and wont hold a screw

We use 2x4s. this way we have good lumber to screw the panels to and the screws thru the panels do not go thru the deck. Also able to shim and straighten out sags.

Condensation isnt an issue here but we do use vented closures and also make sure the attic is vented well. basicly a cold roof. 
The end result is lower attic temps as much as 50 degrees with a white roof , and little chance of leaks or blow-off

We do offer insulation but most people would rather have it over the ceiling.


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## Joasis (Mar 28, 2006)

We have done it about every way possible, plus, the best results are by doing 2x4's combined with solar guard insulation, foil side up. Knocks the heat out of the attic.


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## Ninjaframer (May 28, 2011)

I wont put metal over shingles. I have a similar job coming up and told the customer if he wanted the metal on top of the shingles call someone else. I dont trust the washers to seal unless directly set into hard surface.


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## Randy Bush (Mar 7, 2011)

Red Adobe said:


> direct lay: you'd want to paper over the shingles so they dont rub......and theres always a chance of running a screw into a soft spot or joint and it not holding or setting the washer and leaking. This has happened alot around here and is very hard to fix once the roof deck is rotted and wont hold a screw
> 
> We use 2x4s. this way we have good lumber to screw the panels to and the screws thru the panels do not go thru the deck. Also able to shim and straighten out sags.
> 
> ...


When using 2x do you use closures on the eves? which I think is a must to stop water or such from blowing up under the roof.


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## Brian Peters (Feb 2, 2011)

Joasis said:


> We have done it about every way possible, plus, the best results are by doing 2x4's combined with solar guard insulation, foil side up. Knocks the heat out of the attic.


I'm assuming you put the solar guard on top of the 2x4's . I have done that, always wondered about the screws sealing properly, that insulation seems "squishy "


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## kage (Aug 17, 2008)

Randy Bush said:


> When using 2x do you use closures on the eves? which I think is a must to stop water or such from blowing up under the roof.


we put gable metal on or rake metal, over top of sheet and down barge board..never had a problem with water blowin in, usually we tear down to deck tho...


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## Tom Struble (Mar 2, 2007)

Brian Peters said:


> I'm assuming you put the solar guard on top of the 2x4's . I have done that, always wondered about the screws sealing properly, that insulation seems "squishy "


if it's not facing an airspace or if its in contact with the roof panel it's not doing jack as a radiant barrier[as the name suggest]


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## stombaugh85 (Jul 23, 2012)

I've always used foam strips over shingles then installed the steel. Never had any problems. I think marco industries make them. This of course is only if the deck is solid and no signs of water damage.


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## Joasis (Mar 28, 2006)

Tom Struble said:


> if it's not facing an airspace or if its in contact with the roof panel it's not doing jack as a radiant barrier[as the name suggest]


As you have probably noticed in pictures of our roofs, we will not deck, but instead run 2x's as purlins, solar guard on top, and metal on this. I have heard from many people that this won't work, but I have been in attics in full sun, outside temps over a 100 degrees, and had less then 90 inside. Now.... the typical attic in an Oklahoma summer can easily get to 140 degrees, and doesn't after we install the roof in this way. 

Since it doesn't work, (it really does), tell me why it doesn't work? :thumbsup:


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## Tom Struble (Mar 2, 2007)

tell me how it does


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## Brian Peters (Feb 2, 2011)

I think it has more to do with a white roof than that solar guard...


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## Tom Struble (Mar 2, 2007)

if it's installed the way it's supposed to be there is some benefit,if not you may as well leave it rolled up in the attic


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## donerightwyo (Oct 10, 2011)

We don't install anything, unless the previous is stripped:thumbsup:


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## Tom Struble (Mar 2, 2007)

Tom Struble said:


> tell me how it does


i thought so..practicing building science with both hands behind your back i see:whistling


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## JWilliams (Nov 11, 2008)

ding dang dooo


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## Joasis (Mar 28, 2006)

Tom Struble said:


> i thought so..practicing building science with both hands behind your back i see:whistling


Funny guy. huh. :whistling

How it works is this: Solar Guard, or any of the knock offs, have a "foil" side...and very little insulation properties. Just like foil used in your oven, to reflect heat, you are "reflecting" some of the heat coming through the metal (bridging) and keeping it out of the attic. Foil works on radiation also. It does not have to be the full spectrum of light. 

I have not read of any conclusive studies on roofs installed like this, but we have measured temps in many attics before, during, and after, so I speak from what I know works here. 

Sure, color has a lot to do with how hot the roof gets, and galvalume is the best, but every thing you do that helps keep the heat out is a winning situation. 

I will say that it does not help at all in the winter, and had a customer that knew how good it is decline it, saying he wanted his attic warm...helped heat the house.


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## Randy Bush (Mar 7, 2011)

I put a metal roof on a house a few a years ago and the guy swore I made his house colder, He was one of them educated type if you know what I mean. Anyhow after checking out his insulation it did not even cover the 2x4 ceiling joist:no: Had a hard time getting him to believe that was the problem. Thankfully collectedd on the job and moved on . Some people though. :whistling


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## red_cedar (Mar 30, 2005)

The quality of the installation really has nothing to do with tearing off or not tearing off.
Not tearing off, isn't necessarily that much less costly though
( depending on the situation ) It requires preparation to allow the roof to accept the metal successfully.

We do it either way, depends on the homeowner after explaining the pros and cons of both.

Its not metal, but we still have roofs around here that are 80+ years old with asbestos shingles applied over wood shingles, with no felt underneath. ( the asbestos being 80+ yrs. old )

Just recently didn't get a church project that was priced for metal over the old shingles.
The local union company got it. They cut every corner. No underlayment, metal caulked to existing brick flashings.
Cheap Decra granular shingles. They installed them just like they were doing an asphalt shingle with cheap details. 
We priced it up differently, with a better metal shingle.


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