Metal Roof Deck To Existing Shingle Roof Interface

 
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Old 06-07-2016, 11:18 AM   #1
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Metal Roof Deck To Existing Shingle Roof Interface


Application - new porch roof that I am laying out for a backyard porch. Client would like the new porch roof to be of metal roof construction, and not very steep. However, at the ends where the new roof will mate up to the existing roof at the house, it will overlay an existing asphalt shingle roof.

The new metal roof will be approximately 2 vertical to 12 horizontal slope. The existing asphalt shingle roof is approximately 9 vertical to 12 horizontal slope.

Is it practical to have a new metal deck roof that at its high point interfaces to an existing roof, with that roof be asphalt shingles? Can that work?

If so, what details and or precautions need to be taken? If you have reference to any details or illustrations or photos that would be greatly appreciated.

What details or precautions also need to be taken with concerns towards replacing the shingles on the older roof in say 5 to 7 years?


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Old 06-12-2016, 08:00 PM   #2
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Make sure you use long span bridging screws to hold the shingles to the felt at the metal roof junction box.

You may also want to get some roof flux washers to prevent downward pressure on the wassle bolt.


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Old 06-12-2016, 09:08 PM   #3
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Check with the Manufacturer about installing metal roof on a 2/12 pitch.
They may not recommend it. That is very flat for a metal roof.
I would not consider Metal for a roof flatter than a 5/12. You will be chasing leaks for years to come.
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Old 06-12-2016, 09:32 PM   #4
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Why type of metal roof are we talking about? Standing seam? Exposed fastener?


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Old 06-12-2016, 10:21 PM   #5
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Quote:
Originally Posted by jlhaslip View Post
Check with the Manufacturer about installing metal roof on a 2/12 pitch.
They may not recommend it. That is very flat for a metal roof.
I would not consider Metal for a roof flatter than a 5/12. You will be chasing leaks for years to come.
Not necessarily true. I have done fairly flat roofs better with no problems. On a flatter roof the seals need a sealing tape on the laps and stitch screws.
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Old 06-13-2016, 07:58 AM   #6
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Yea.Those wassle bolts are cool.
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Old 06-13-2016, 09:22 PM   #7
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Quote:
Originally Posted by Randy Bush View Post
Not necessarily true. I have done fairly flat roofs better with no problems. On a flatter roof the seals need a sealing tape on the laps and stitch screws.
First site for Metal Roofing Manufacturers that I Googled listed the minimum of a 3/12 pitch. I stopped looking and wrote my comment above after the Google search.
You can Metal Roof all the 2/12 pitch roofs you want to. I won't do it based on my experience of having seen them leak too often.
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Old 06-14-2016, 11:38 AM   #8
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Are you installing this in a cold weather zone? This sounds like you could have some ice damn issues to consider on the low pitch roof to shingle roof interface.

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Old 10-11-2017, 02:58 PM   #9
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Re: Metal Roof Deck To Existing Shingle Roof Interface


Your going to have to go with a 1 3/4" snap lock standing seam that is rated for under a 3/12. My local vendor sells one it goes to a 1/4 / 12 pitch. Use transition trim at the place where they meet . Checkout your local metal vendor and see what trim they have.
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Old 10-16-2017, 08:19 AM   #10
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Re: Metal Roof Deck To Existing Shingle Roof Interface


You can do a screw down roof as flat as 1":12 and a standing seam as flat as 1/4":12 if they are done properly.

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