Minimum Roof Pitch


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Old 05-01-05, 03:49 AM
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Minimum Roof Pitch

I am planning a shed dormer with a roof that will have about 3:12 pitch. What is the recommended minimum roof pitch for conventional 3-tap shingles?
 
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Old 05-01-05, 05:02 AM
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Check with the manufacturer of the shingles you plan to use.
 
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Old 05-01-05, 05:31 AM
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For sure check with the manufacturer. But most go on down below A 3:12.

ED
 
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Old 05-01-05, 06:51 AM
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Originally Posted by Ed Imeduc
For sure check with the manufacturer. But most go on down below A 3:12.

ED
What does "go on down below" mean...steeper or less steep?
 
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Old 05-01-05, 07:04 AM
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I have seen some go down to a 2 1/2 :12 a flater roof.
 
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Old 05-01-05, 02:15 PM
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I have a brother in law who used to be a roofer. I always heard him say that less than 3:12 voided the warrannty. Whether or not that is true I don't know, but you see mobile homes with shingles and 3:12 pitch. I would think any less would be inviting trouble.
my 2 cents probably worth less
 
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Old 05-02-05, 11:42 AM
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I contacted the shingle manufacturer and they said:

"The minimum pitch for all GAF shingles is 2:12. However, be sure to follow the low-slope application instructions which include a 19" overlap of the underlayments for slope that low."

By the way, with some framing help from DIY Forum I got the slope increased to nearly 3-1/2:12 so it's full speed ahead for this project.
 
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Old 05-02-05, 12:01 PM
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Even though you can lay the 3-tabs down to a 2/12, you're asking for trouble if you don't either cover the entire area with a membrane first, or at LEAST 2 layers of felt....with EXTRA-WIDE drip edge flashings.

Have replace many...many MANY shingled-covered low-pitched areas, complete with new wood decking because of water seepage.....due to extremely low pitch.
 
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Old 05-09-05, 07:26 AM
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Most manufacturers follow this general rule:

Anything 2:12 to 4:12 can use composition shingles, but MUST have either 2 layers of felt or a waterproofing membrane (ice & water shield).
I would STRONGLY suggest using the waterproofing membrane. The manufacturers may allow 2 layers of felt, but, like E. Dodge indicated, I personally think you're inviting a problem.....just my opinion.

Anything 4:12 and over can use standard underlayment under the composition shingles.

Good luck.
 
 

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