2/12 slope for shingles

**JIM MURPHY** · 10-25-2011, 04:35 PM

Is it possible to have a 2/12 sloped roof shingled? If so, what is the criteria?

Also what if they used a ice and water underlayment? Would that be acceptable with shingles if they decreased the exposure?

The house is ocean front.

Jim

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**Jerry Peck** · 10-25-2011, 04:39 PM

Originally Posted by JIM MURPHY

Is it possible to have a 2/12 sloped roof shingled? If so, what is the criteria?

Yes, some manufacturers allow down to a 2/12 slope as I recall. How? According to their installation instructions.

I believe the underlayment is doubled over what is normally called for.

Also what if they used a ice and water underlayment? Would that be acceptable with shingles if they decreased the exposure?

Might work and might be acceptable, you would need to check the manufacturer's installation instructions.

**Jack Feldmann** · 10-25-2011, 07:12 PM

2/12 is the minimum slope for shingles

**Jerry Peck** · 10-25-2011, 08:41 PM

Originally Posted by Jack Feldmann

2/12 is the minimum slope for shingles

You sure?

The ones I recall are 2-1/2 in 12 or 3 in 12, as I recall (although it has been a while since I have looked as I have not found shingles on that low of a slope in years.

**Joseph Hagarty** · 10-25-2011, 08:46 PM

A shingle installation on anything less than 4 / 12 in this area,
I recommend a roofer review along with repairs to correct deficiencies.

Snow loads the last couple of winters have been incredible.

your mileage may vary.....

**John Dirks Jr** · 10-25-2011, 09:51 PM

Chapter 9 - Roof Assemblies

IRC is the same language too.

**Michael Thomas** · 10-26-2011, 05:43 AM

Typically, the manufacturer's installation instructions are going to recommend or require upgraded underlayment, and reference the appropriate ASTM standards.

I tell clients "In my opinion, in our climate at 2/12 the shingles are a 'decorative roof covering', and it's the underlayment providing the water resistance".

**John Kogel** · 10-26-2011, 09:51 AM

Originally Posted by Michael Thomas

Typically, the manufacturer's installation instructions are going to recommend or require upgraded underlayment, and reference the appropriate ASTM standards.

I tell clients "In my opinion, in our climate at 2/12 the shingles are a 'decorative roof covering', and it's the underlayment providing the water resistance".

What about all the shingle nail holes in your nice underlayment?

Nobody shingles a 2 in 12 in my area, the wild Wet Coast. It would leak. Period.
A few years back, I saw a 3 in 12 shingled and I called it suspect. The shingle exposure should be reduced an inch or more for 3 in 12. Forget about anything like 2 in 12. That would need torch-on modified bitumen. At least, that is what they do here.

**Michael Thomas** · 10-26-2011, 12:38 PM

Originally Posted by John Kogel

What about all the shingle nail holes in your nice underlayment?

In my experience, here in Chicago properly self-adhesive WSU is sufficiently self-healing to work successfully under comp shingles installed at any slope allowed by the manufacturer.

Which is not to say that I think such installations between 2/12 - 4/12 are a Good Idea, but only that 1) I personally have not seen them fail due to water intrusion through the underlayment and 2) I cannot fault them for violating the manufacturer's installation instructions.

More often, I'm writing them up at HIs or WIs because the underlayment does not even meet the manufacturer's installation requirements or R905.3.3.1 and/or because of flashing or similar details - I should be so lucky as to find WSU!