# Reroofing



## alaskajoe (Aug 16, 2019)

Can someone give me their interpretation of R907.3 Exception 1? I have a guy who has a roof with 2 layers of asphalt shingles and wants to put a metal roof on top of it. Just not sure what they mean  with the words "transmit the roof load directly to the buildings structural system". Its a 12/12 pitch so there should be no snow build up.


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## jar546 (Aug 16, 2019)

alaskajoe said:


> Can someone give me their interpretation of R907.3 Exception 1? I have a guy who has a roof with 2 layers of asphalt shingles and wants to put a metal roof on top of it. Just not sure what they mean  with the words "transmit the roof load directly to the buildings structural system". Its a 12/12 pitch so there should be no snow build up.



Do you mean 907 or 908?


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## jar546 (Aug 16, 2019)

908.3.1.1(3) is your answer.  No no roof over 2 existing layers regardless of the type.  Clear and concise.


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## alaskajoe (Aug 19, 2019)

jar546 said:


> 908.3.1.1(3) is your answer.  No no roof over 2 existing layers regardless of the type.  Clear and concise.


We are still on 2012 IRC so it is covered 907.3 It has an exception 1 which is the same as 908.3.1 (2). I just wonder what they mean by that rule.
I agree that 908.1.1(3) is going to be the call on this application.


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## my250r11 (Aug 19, 2019)

My BO here Interpretation is 908.3.1 exc 2 & 3 allows for the metal panels if installed with proper length fasteners. The last part of exc. 2 does say "existing roof coverings"


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## Pcinspector1 (Aug 19, 2019)

alaskajoe said:


> I agree that 908.1.1(3) is going to be the call on this application.



OP said asphalt shingles, exception number 3, sez *existing spray polyurethane foam *roofing systems. Am I mis interpolating the information provided?


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## alaskajoe (Aug 19, 2019)

It does say existing roof coverings but are we not increasing the dead load even more with a layer of roofing metal on top if two layers of asphalt shingles. Even if you have long enough fasteners it is still more weight. And if this house is on its third roof it might be time to get the two layers of shingles off and inspect the substrate.
I am not going to allow it to happen


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## classicT (Aug 19, 2019)

alaskajoe said:


> It does say existing roof coverings but are we not increasing the dead load even more with a layer of roofing metal on top if two layers of asphalt shingles. Even if you have long enough fasteners it is still more weight. And if this house is on its third roof it might be time to get the two layers of shingles off and inspect the substrate.
> I am not going to allow it to happen





my250r11 said:


> My BO here Interpretation is 908.3.1 exc 2 & 3 allows for the metal panels if installed with proper length fasteners. The last part of exc. 2 does say "existing roof coverings"



The plural nature of the word "coverings" is because of the plural nature of the roof covering. Is a roof covered with a shingle or shingles, standing seam panel or panels, etc. While roof covering sounds ok, it is in fact grammatically incorrect.


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## jar546 (Aug 19, 2019)

alaskajoe said:


> It does say existing roof coverings but are we not increasing the dead load even more with a layer of roofing metal on top if two layers of asphalt shingles. Even if you have long enough fasteners it is still more weight. And if this house is on its third roof it might be time to get the two layers of shingles off and inspect the substrate.
> I am not going to allow it to happen



The code and common sense prevail.


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## mtlogcabin (Aug 19, 2019)

Depends on the metal roofing system
2012 IRC
R907.3 Recovering versus replacement.
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.


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## alaskajoe (Aug 19, 2019)

So your saying that by looking at exception 1 in R907.3 of 2012 you can just put roofing metal over two layer of asphalt shingles with long screws?


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## mtlogcabin (Aug 19, 2019)

No You will need to install purlins attached to the rafters/trusses to support the metal roof which will then transfer the roof loads to the supporting structure. The idea is to keep the new metal roof covering from increasing the dead load on the roof sheathing. Remember all the roof sheathing charts only use a 10 psf for dead load which is built into the total load numbers in the tables. That is why you are only allowed 2 layers of asphalt roofing

a.    The allowable total loads were determined using a dead load of 10 psf. If the dead load exceeds 10 psf, then the live load shall be reduced accordingly.


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## alaskajoe (Aug 19, 2019)

That is what I was driving at. I think that exception is confusing.
Thanks for the clarity.
my answer is still no. Tear the two layers of shingles off.


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## my250r11 (Aug 20, 2019)

903.1 exc. 3 also says can be installed over wood shingle, and I haven't been anywhere they allow anything to overlay wood shingles.

I have to follow what the BO allows.


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## JCraver (Aug 22, 2019)

mtlogcabin said:


> Depends on the metal roofing system
> 2012 IRC
> R907.3 Recovering versus replacement.
> 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.





mtlogcabin said:


> No You will need to install purlins attached to the rafters/trusses to support the metal roof which will then transfer the roof loads to the supporting structure. The idea is to keep the new metal roof covering from increasing the dead load on the roof sheathing. Remember all the roof sheathing charts only use a 10 psf for dead load which is built into the total load numbers in the tables. That is why you are only allowed 2 layers of asphalt roofing
> 
> a.    The allowable total loads were determined using a dead load of 10 psf. If the dead load exceeds 10 psf, then the live load shall be reduced accordingly.



This is the correct answer / interpretation of the code.  If you're screwing metal panels to the roof deck directly over the shingles then you're adding a third layer and it's a no-go.  BUT, if you're adding purlins attached to the roof framing and then installing metal panels onto the purlins, then I don't care if there's 4 layers of shingles over wood shakes, you're good to go.  That's what the code says, so that's what you get to do. (In the 15 IRC it's 908.3.1 exc 2).


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## alaskajoe (Aug 22, 2019)

JCraver said:


> This is the correct answer / interpretation of the code.  If you're screwing metal panels to the roof deck directly over the shingles then you're adding a third layer and it's a no-go.  BUT, if you're adding purlins attached to the roof framing and then installing metal panels onto the purlins, then I don't care if there's 4 layers of shingles over wood shakes, you're good to go.  That's what the code says, so that's what you get to do. (In the 15 IRC it's 908.3.1 exc 2).


That makes total sense. Easier and cheaper to tear the two layers of shingle off anyway I would think. I told homeowner it was a no go and he is going to tear old roofing off.


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## ADAguy (Aug 22, 2019)

At what point do the additional weight of sheathing/waterproof membrane and rigid insulation possibly come into play, where there was none ?


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## north star (Aug 29, 2019)

*# ~ # ~ # ~ #*

Can the purlins be 1" x 4" strips of non-pressure treated wood
attached to the roof structural components, ...or 2" x 4"'s,
...or pressure treated, ...or metal hat channel strips, or plastic
strips bolted to the roof structural, or other ?

*# ~ # ~ # ~ #*


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## edseven (Sep 16, 2019)

What I've learned is that you cannot put standing seam on top of two existing covers. The exception for structural metal standing seam does not apply to architectual standing seam that lays on top of the existing covers. It must be self supporting.

What I need to know is this: If the code allows a recover because I have one layer of shingles and I am adding standing seam do I have to follow the rest of the code with regards to roofing. Do I need to put down ice and water shield. Does my underlayment go over or under the drip edge. If the mgf does not RECONMEND installing standing seam over shingles can I still do it?


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## ADAguy (Sep 16, 2019)

"If" not recommended, then why would you if it voids warranty?


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## e hilton (Sep 16, 2019)

edseven said:


> If the mgf does not RECONMEND installing standing seam over shingles can I still do it?


If the mfgr is completely silent on the issue, you could but why not do it right?  If the mfgr says either “not recommended” or “not allowed” ... and you do it anyway ... kiss the warranty goodbye.  

Something i kept in mind when i did projects for customers: the quality remains long after the price is forgotten.


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## ICE (Sep 16, 2019)

Recommending has no authority.  Nearly every roofing material warranty covers the product and only the product. The manufacturer does not concern itself with what people do with the product beyond installation instructions.  You can do everything right or everything wrong and the warranty is still in force.  The only thing that a warranty can cover with a metal roof is the paint.    As long as the paint stays on, there's no warranty claim.


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## edseven (Sep 16, 2019)

I'm just trying to find out two things. Does all of the code apply to the roof if recover is allowed? Does it should need proper flashing and I&W shield?

The mfg does not reconmend installing standing seam over shingles. The code allows it. The mfg is more strict. Does it overrule the code?


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## ADAguy (Sep 17, 2019)

Do you want a warranty or not? Code compliance is not a warranty of durability.


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## edseven (Sep 17, 2019)

What is your point?


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## edseven (Sep 17, 2019)

Can you use cement board screws for hidden fastener clips?


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## MindalBoom (Oct 7, 2019)

Good contractors have a good guarantee, not only for paint, but it’s an exaggeration. When I turned to metal roofing in Toronto during a conversation they explained to me that the guarantee depends on the parameters of my roof, under what conditions there is a house, and received an answer that completely satisfied me, I can’t say how much, but this is more than others suggested.


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## mark handler (Oct 7, 2019)

Follow the metal roofing system manufactures instalation instructions.
Some will allow it some, based on condition of shingles below some manufacturers do not recommend it, smooth substrate. it is also harder to deal with roof penitrations and attic ventilation.

Fire departments have told me they hate metal roofing system because if the fire is burning below the metal roofing systems act like a frying pan, heating up, but preventing the water from getting to the fire. They are also very slippery even when not wet.


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## ADAguy (Oct 8, 2019)

Points well made, but they do have their place and last for decades.


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