Thread: 5V galvanized roof over shingles

I talked to a home inspector I know before installing a new metal roof over existing shingles. He lives in NY, not in AL, and he didn’t research the subject much.
Per many manufacturers, 5V requires solid decking, 29 or 26 gauge, as it is not structural. My plan is to install 8 ft. Galvanized Steel 5V Crimp Roof Panel (Fabral, 29 GA) from Home Depot over existing shingles using 1x4 with not less than 24” spacing, covered with Tyvek. The problem is, some building inspectors strictly follow solid decking rule: http://www.inspectionnews.net/home_i...lled-1x4s.html
But, it is hard to argue that any existing shingle roof has solid decking, properly attached to trusses. It is not a barn with open trusses where that rule makes a lot of sense; you can’t break the panels when step on them when they are on top of a shingle roof (you can bend them a little bit, like all small gouge galvanized roof panels, 5v or not, but I don’t have plans to walk on roof after it is done without protection boards as required).
What is your opinion? As far as I know our area uses International Code, and it is OK per Code to put metal over shingles.
Metal roof manufacturers mention “solid decking” rule in their installation manuals, but provide instructions how to install 5V over the shingles the next page.
Thank you

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Originally Posted by John Sebastian

I talked to a home inspector I know before installing a new metal roof over existing shingles. He lives in NY, not in AL, and he didn’t research the subject much.
Per many manufacturers, 5V requires solid decking, 29 or 26 gauge, as it is not structural. My plan is to install 8 ft. Galvanized Steel 5V Crimp Roof Panel (Fabral, 29 GA) from Home Depot over existing shingles using 1x4 with not less than 24” spacing, covered with Tyvek. The problem is, some building inspectors strictly follow solid decking rule: http://www.inspectionnews.net/home_i...lled-1x4s.html
But, it is hard to argue that any existing shingle roof has solid decking, properly attached to trusses. It is not a barn with open trusses where that rule makes a lot of sense; you can’t break the panels when step on them when they are on top of a shingle roof (you can bend them a little bit, like all small gouge galvanized roof panels, 5v or not, but I don’t have plans to walk on roof after it is done without protection boards as required).
What is your opinion? As far as I know our area uses International Code, and it is OK per Code to put metal over shingles.
Metal roof manufacturers mention “solid decking” rule in their installation manuals, but provide instructions how to install 5V over the shingles the next page.
Thank you

John, my advise is to re-think the idea of the second roof, regardless of type. This is from hard learned experience. If a leak does develop it is very difficult to find its origin with a second roof. Spend the extra money now and do a tear off.

Originally Posted by Vern Heiler

John, my advise is to re-think the idea of the second roof, regardless of type. This is from hard learned experience. If a leak does develop it is very difficult to find its origin with a second roof. Spend the extra money now and do a tear off.

Thank you very much for your reply. My current shingle roof is in a good shape, no leaks. The roof is very simple, with 4 vents only. Don't think it may leak if installed properly. If it does, looks like it is better to keep existing covering as well... It is more a code issue I guess. Thanks again

OK, here is International code I found online (please correct me if I'm wrong):
R907.3 Recovering versus replacement. New roof coverings shall not be installed without first removing all existing layers of roof coverings where any of the following conditions exist:


1. Where the existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile.3. Where the existing roof has two or more applications of any type of roof covering.4. For asphalt shingles, when the building is located in an area subject to moderate or severe hail exposure according to Figure R903.5.

Exceptions:1. Complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to transmit the roof loads directly to the building's structural system and that do not rely on existing roofs and roof coverings for support, shall not require the removal of existing roof coverings.2. Installation of metal panel, metal shingle and concrete and clay tile roof coverings over existing wood shake roofs shall be permitted when the application is in accordance with Section R907.4.3. The application of new protective coating over existing spray polyurethane foam roofing systems shall be permitted without tear-off of existing roof coverings.That's the way I understand that:
There are only 4 reasons, when you have to remove the old roof covering. Yes, there is Exception 1 for metal roofs that rely on existing roof for support (I guess non-structural 5V does that), but that exception is only in-place when one of the 4 main reasons is there to remove the covering and and you have to do follow it (bad roof, 2 layers, hail area, clay/cement/slate/shake roof).

Since it looks like I have only 1 layer of shingles, I don't have to remove it to begin with looks like.

Thank you

Originally Posted by James Risley

It's actually more of an issue of getting a new roof which will look good for many years and also have a warranty as well as having a roof which is insurable. Not a roof which will appear uneven if someone accidentally steps off the walk board and pulls the lap apart and bending the v lap....introducing a leak at that point. Could also void insurance coverage in some instances. If you are worried about not having a vapor barrier between the metal roofing and the solid decking....simply install a vapor barrier instead of the tyvek. Or you might consider 1/2 inch dow or corning closed cell sheathing (being sure to tape the joints) applied directly over the existing shingles. Do not forget that condensation will occur on the underside of the metal roofing when the dew point is reached. The more the air space=====the more condensation can occur. The closed cell sheathing should provide a solid base under the 5v panel.

Actually, foam sheathing may be a great idea for an extra insulation to begin with. The question is: if screws hold OK when the panels are on top of it - it is soft and may let the panels to get loose over time. Step on it, and I see a chance to dent the foam board and re-screwing the panel.

"In re-roofing jobs where the condition of the old decking is in question,

or where existing shingles will be left in place, new 2x4 purlins should
be fastened through the decking and into the rafters. This will provide

a solid framework for attaching the metal panels." - it is per Fabral, the manufacturer. They don't want shingles to scratch the coating I guess.

I understand, that no shingles and new vapor barrier is a way better than a layer of shingles. But I will have to do the roof alone, with no helpers (I'm broke ) and it is already a lot for me to handle. I will have only 10 days of vacation to finish the project, so I have to go the easiest way that is per code.
Nobody is walking that roof to damage it, and if it happens - those panales are only $15 at Lowes to replace it.
Thanks again

"In re-roofing jobs where the condition of the old decking is in question,

or where existing shingles will be left in place, new 2x4 purlins should
be fastened through the decking and into the rafters. This will provide

a solid framework for attaching the metal panels." - it is per Fabral, the manufacturer. They don't want shingles to scratch the coating I guess.

John, on pg. 2 of the Fabral installation instructions it has "(note that 5V requires solid decking)" so the use of 2X4 purlins does not apply.

(bold and underlining in both of the below quotes are mine)

Originally Posted by John Sebastian

My plan is to install 8 ft. Galvanized Steel 5V Crimp Roof Panel (Fabral, 29 GA) from Home Depot over existing shingles using 1x4 with not less than 24” spacing,

Vern has your answer right here:

Originally Posted by Vern Heiler

John, on pg. 2 of the Fabral installation instructions it has "(note that 5V requires solid decking)" so the use of 2X4 purlins does not apply.

Final answer: Not allowed by code or by manufacturer.

Originally Posted by Jerry Peck

(bold and underlining in both of the below quotes are mine)


Vern has your answer right here:


Final answer: Not allowed by code or by manufacturer.

Could you please specify the code paragraph that says that it is not allowed? I tried to find it and was unable to.

Manufacturer - it is not so simple. I called Fabral and they sent me to a local building authority for the final answer, their manual is just recommendations. That is no helpful to me: because of budget cuts, we have a single inspector now and frankly speaking as soon as gas line, wiring and frame are fine, my roof is going to be approved.

But, going back to the original question. What do you think "solid decking" is? Is shingle roof over OSB is a solid decking?


Thank you again for all your help

Originally Posted by James Risley

It may get walked during the final roofing inspection.
The screws in any case will have to go through all roofing and insulation and into the decking. The decking needs to be good enough to hold the screws. If the decking is not good enough, then new purlins either 1x4 or 2x4 (probably 2x4 for code) will have to be fastened to rafters. The roofing fasteners then will only need to reach the purlins. Get approval of what you want to do when you take out the permit. They will tell you what they expect.

I think the owens pink 1/2 inch sheathing panels are rated at 18psi compressive. Walking the roof with it under the metal should not be a problem. If the fastener reaches properly through adequate decking then the fastener should not loosen. The closed cell sheathing panel in this case should be thought of more as a vapor barrier and not as insulation.

Scratching the panel is of some concern but I believe that the main concern from applying the panel directly over the composition roofing is the petroleum products in the shingles evaporating when the metal gets hot and then condencing on the metal panel, resulting in discoloring of the finish near the edges and ends of the roofing panels.

If you are broke and the roof is not leaking and you are reroofing .....then why?????

The roof is 25 yo, it is of a nasty color, and all my neighbors have metal roofs. I plan to sell the house in 2-3 years so it is needed.
Nobody I know gets permits on roof recovering, metal or shingles - it is rural Alabama, not NY or VA.
Do you think closed cell sheathing applied over shingles counts as solid decking?

Thank you very much

Originally Posted by Vern Heiler

"In re-roofing jobs where the condition of the old decking is in question,

or where existing shingles will be left in place, new 2x4 purlins should
be fastened through the decking and into the rafters. This will provide

a solid framework for attaching the metal panels." - it is per Fabral, the manufacturer. They don't want shingles to scratch the coating I guess.

John, on pg. 2 of the Fabral installation instructions it has "(note that 5V requires solid decking)" so the use of 2X4 purlins does not apply.

Thank you. Do you think shingle roof over OSB is a solid decking? I asked Fabral, but they told me it has to be assessed by a local authority. As I said before, my local authority is going to approve it since he is overloaded and there is no danger.

Originally Posted by John Sebastian

Thank you. Do you think shingle roof over OSB is a solid decking? I asked Fabral, but they told me it has to be assessed by a local authority. As I said before, my local authority is going to approve it since he is overloaded and there is no danger.

OSB is solid decking. If you install purlins, you are no longer installing the panels on solid decking.

If you install the panels on top of the shingles you are not following the manufactures instructions. Might not cause a problem until your buyer has the home inspected by one of us. If the inspector knows it is wrong it could cause you to have a negotiation of price of sale. Could cost you more than the cost to have someone tear off and dispose of the shingles now.

Thank you for all your help

Originally Posted by John Sebastian

Could you please specify the code paragraph that says that it is not allowed? I tried to find it and was unable to.

The code require that all products be installed as they are listed, labeled and tested, which means to install the products in accordance with their product approval and their installation instructions.

Manufacturer - it is not so simple. I called Fabral and they sent me to a local building authority for the final answer, their manual is just recommendations.

Their manual are code by reference. Some manufacturer use the word 'recommend' in telling how to install their products, but the code says to do it the way the manufacturer says to do it, thus "recommend" becomes "shall" ... i.e., it is not a "recommendation" it is a "shall do it this way".

John
I do not recommend putting any metal roofing over existing shingles. Even though the manufacture says that you can put it directly over the shingles. And most of the roofers that install the metal roofing say that is is fine. It has been known to have to many problems.
Remember you are not stopping the aging process of the shingles. They are still deteriorating. Check the temperature of that metal roof on that hot sunny day. The screws that you use to secure the metal become loose and start to leak after five to ten years. That 55 year roof needs to be replace after 10 and with it allot of decking. And the manufacture says its not there metal that is bad, but the fastener. What do you do.
I recommend that the shingles be removed down to the deck, boards laid down and secured for the metal roofing material. The fasteners that you use are a good fastener that is going to last for the life of the metal roof. Barn nails not a good choice.
I have found issues with most metal roofs that is installed over the shingles. They are going to leak. Yes the manufacture says it is OK to install it over the shingle. Their not going to do anything when the roof leaks. It's your problem. Do it right, your better off.
Bruce Adams

Originally Posted by John Sebastian

I talked to a home inspector I know before installing a new metal roof over existing shingles. He lives in NY, not in AL, and he didn’t research the subject much.
Per many manufacturers, 5V requires solid decking, 29 or 26 gauge, as it is not structural. My plan is to install 8 ft. Galvanized Steel 5V Crimp Roof Panel (Fabral, 29 GA) from Home Depot over existing shingles using 1x4 with not less than 24” spacing, covered with Tyvek. The problem is, some building inspectors strictly follow solid decking rule: http://www.inspectionnews.net/home_i...lled-1x4s.html
But, it is hard to argue that any existing shingle roof has solid decking, properly attached to trusses. It is not a barn with open trusses where that rule makes a lot of sense; you can’t break the panels when step on them when they are on top of a shingle roof (you can bend them a little bit, like all small gouge galvanized roof panels, 5v or not, but I don’t have plans to walk on roof after it is done without protection boards as required).
What is your opinion? As far as I know our area uses International Code, and it is OK per Code to put metal over shingles.
Metal roof manufacturers mention “solid decking” rule in their installation manuals, but provide instructions how to install 5V over the shingles the next page.
Thank you

I haven't heard good things about Tybek form the local builders; many are swithching to other brands.... just what I hear....

Originally Posted by James Risley

House brands of house wrap can be less than half the cost of of Tyvek. One good reason for some builders to switch. Quality differences - short term vs long term ?????? dunno.....

... I mean in terms of performance other than cost...