Roof Slope

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Old 11-29-20, 07:00 AM
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Question Roof Slope

I had a contractor come out to provide an estimate on replacing soffit on a rental property. I had assumed icicles were forming due to a lack of airflow. The contractor took one look and said that the roof was at such a low pitch that it shouldn't have even been shingled. He said water was travelling back up under the edge of the shingles in places and causing the icicles. He pointed out where it was likely happening and I observed it happening later during a light rain. As I recall, 40 years ago the roof didn't have shingles but was tarred and had a layer of pebbles on it. The contractor suggested that the shingles be removed and a metal roof installed.

Is there a tolerance for roof pitch when applying shingles?
Is a metal roof really the preferred covering on low pitched roofs?

thanks
 
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Old 11-29-20, 07:08 AM
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most shingle manufactures require a minimum slope of a 3/12 pitch [3"rise over 12"]
metal roofs will work with less slope
 
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Old 11-29-20, 07:22 AM
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The minimum slope is actually 2:12. They specify that the underlayment (felt) be lapped 19" if the slope is between 2:12 - 4:12. This step is often overlooked.
 
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Old 11-29-20, 08:07 AM
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After doing a bit more research it seems that the preferred method for shingling a roof that is between 2-4:12 is to avoid the overlap felt and using asphalt cement on every seam as contractors either don't do it properly or bid without it. Instead it is recommended to use a synthetic membrane.
 
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Old 12-06-20, 10:14 AM
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Question

After receiving an estimate for $22k to put a TPO membrane on my 2k sqft roof I did some more research and measured the pitch of the roof myself. It's 1.5:12.

So shingles are not going to happen and shouldn't have been put on the roof in the first place.

My research shows the only options are metal, TPO, EPDM or PVC with PVC and metal being the longest lasting.

I think my only option is metal because if I understood the application of PVC correctly I would have to have all 3 layers of existing shingles AND the original hot tar roof removed because the PVC cannot be in contact with any petroleum based products. The shingle/tar removal would add about $6k to the cost. The estimate I got for a metal roof only discussed removing one layer of shingles.

So my question for a metal roof is, due to the low pitch am I limited to metal panels or could I have metal shingles?

Any other words of wisdom most welcome.

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Old 12-06-20, 10:58 AM
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Typically on any low slope with a metal roof, you first cover the deck with a high temp ice and water shield, then you apply the metal roof. And as far as metal shingles are concerned, you would defer to their instructions... they all may have different minimum requirements.
 
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Old 12-07-20, 09:59 AM
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Sorry for the questions but it's getting to be like dealing with used car dealers what with the differing "recommendations" from the individual contractors.

So the latest is that due to the pitch of my roof (1.5:12) a "commercial grade" metal would have to be used which is "more expensive than a TPO roof". This from the same contractor that gave me an estimate for a $22k TPO roof. I understand that there are different grades of metal roofing and different methods in their construction (lapped or standing seam) but it sounds like this guy has a target amount for how much he wants to separate from my billfold.
 

Last edited by sybaris; 12-07-20 at 10:54 AM.
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Old 12-07-20, 04:54 PM
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IMO, TPO is probably what your target should be. There is no sense doing a metal roof when it's going to be so flat that no one will see it unless they are in an airplane.

Shop around and call commercial roofers and see if they will give you a ballpark estimate on your sq ft.
 
 

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