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Reroof metal over asphalt shingle

J

jharrison

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Joined
Apr 1, 2021
Messages
12
Location
Iowa
trying to find reference for placing metal over asphalt shingles.
Furring Strips required or No
 
You'll have to check you're local codes and AHJ. I don't think metal roofing can go over asphalt shingles in any case. If residential in my city I would cite R905.1 and R905.10. Besides meeting code requirements products must also follow manufactures directions.
 
The code does not say "...over asphalt shingles"

R908.3.1 Roof Recover
"...The application of a new protective roof coating over an existing protective roof coating, metal roof panel, metal roof shingle, mineral surfaced roll roofing, built-up roof, modified bitumen roofing, thermoset and thermoplastic single-ply roofing and spray polyurethane foam roofing system shall be permitted without tear-off of existing roof coverings...."
 
There are some metal roofs that are designed to be installed over an existing roof. I think most of them have furring or spacers.

You will need some way to secure the metal roof to meet uplift requirements.
 
mark handler said:
The code does not say "...over asphalt shingles"

R908.3.1 Roof Recover
"...The application of a new protective roof coating over an existing protective roof coating, metal roof panel, metal roof shingle, mineral surfaced roll roofing, built-up roof, modified bitumen roofing, thermoset and thermoplastic single-ply roofing and spray polyurethane foam roofing system shall be permitted without tear-off of existing roof coverings...."
Click to expand...
Would asphalt shingles be a protective roof covering?
 
I recall reading somewhere that under certain conditions the space between the metal roof and the existing roof shall be fire-stopped. It might have been if the existing roof was wood shingle or shake.
 
After re-reading the relevant code sections I see that this is yet another interpretation based call. I think it comes down to the manufactures instructions. If a licensed contractor showed me that their product can be installed over shingles I would probably have to approve it. However, I think it's a bad idea. Without a tear-off you don't really get a good look at the decking, you don't replace any flashing or flues, and if there is unseen damage it will be much harder to track down and repair later. If someone wants to invest in metal roofing (vs replacing with another shingle roof) why not spend the extra money to be sure the decking is solid, flashing replaced, proper underlayment installed, etc... But to each their own I suppose.
 
ICE said:
I recall reading somewhere that under certain conditions the space between the metal roof and the existing roof shall be fire-stopped. It might have been if the existing roof was wood shingle or shake.
Click to expand...
Maybe it was: R908.4 requires the entire existing surface to be covered with gyp board, mineral fiber, glass fiber or other approved material.
 
e hilton,
R908.4 new roof covering over WOOD shingles or shakes, I'm bit off topic.
 
I would think it would be easier to strip the wood shingles and deck the rafters, rather than trying to cover them up, fire rate them, and provide a level surface for the metal.
 
ICE said:
Would asphalt shingles be a protective roof covering?
Click to expand...
In my read of that section, they are defining what a protective roof coating is. Otherwise they would not have listed any of those other, protective roof coatings.
 
Joe.B said:
After re-reading the relevant code sections I see that this is yet another interpretation based call. I think it comes down to the manufactures instructions. If a licensed contractor showed me that their product can be installed over shingles I would probably have to approve it. However, I think it's a bad idea. Without a tear-off you don't really get a good look at the decking, you don't replace any flashing or flues, and if there is unseen damage it will be much harder to track down and repair later. If someone wants to invest in metal roofing (vs replacing with another shingle roof) why not spend the extra money to be sure the decking is solid, flashing replaced, proper underlayment installed, etc... But to each their own I suppose.
Click to expand...
Good advice & best practice
 
mark handler said:
In my read of that section, they are defining what a protective roof coating is. Otherwise they would not have listed any of those other, protective roof coatings.
Click to expand...
Ya I'm not with you on that. Asphalt shingles are a protective roof covering and the most likely candidate for a first and second layer.
 
I would reach out to the Mfr first and foremost. There are special high temp underlayments & high temp ice and water shield products that need to get used with metal roofing because the standard products will melt from the heat generated by the metal roof. There is a chance that the same could happen with asphalt shingles.
 

DO I NEED UNDERLAYMENT FOR A METAL ROOF OVER SHINGLES?​

All roofs need an underlayment. If you’re installing a metal roof over asphalt shingles, the shingles may be able to act as an underlayment for the roof. However, the shingles expanding and contracting can cause damage underneath the metal roof over time. For this reason, it’s usually recommended that you remove the shingles on your home before installing a metal roof.

WHAT IS THE BEST WAY TO INSTALL A METAL ROOF OVER SHINGLES?​

If you wish to install metal roofing over shingles, it’s recommended to do it one of two ways. The first is to apply an approved underlayment over the old shingles. This is the fastest way to install but it doesn’t provide the flattest surface for metal roofing installation. The second way is to install 1×4 purlins over the shingles. This is more expensive but will also be higher quality.

When constructing my house which took about 4 years I used 90 lb rolled roofing until I was ready to install the metal roof system. This was Fabral's response in 2006 when I purchased their product for my house. Since I did not use shingles I chose just apply another underlayment over the rolled roofing material
 
My opinion is a overlay on anything is bad news/false economy, a lot of good reasons not to leave existing roofing material in place have been mentioned in previous posts.
 
I feel that you should start at the deck with all re-roofs. This is my opinion thou not the code. The code allows overlays. The BO here allows to overlay shingle with an underlayment and proper length fasteners. We live in an Hot and windy area. Most use R panel. We have had very few blow off. Mostly ones w/o permits and the fasteners were to short.
 
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