Minimum roof pitch on shed lean-to...

[mpwedge]

I am planning a 12x16 shed with a lean-to coming out 12' on one side. I am trying to get the max height out of the lean-to that I can, what is the minimum roof pitch for asphalt shingles? I could go with a metal roof, but would rather explore asphalt as the rest of the shed is asphalt on a 7/12 roof. I have read that 2/12 is do-able using a ice water barrier and double layers of felt. Does the fact that its a 12x16 roof change anything?
I'm in the Willamette Valley in oregon between Salem and Portland, we do get rain and occasionally snow, but I haven't seen more than 12" at one time over the 20 years that we've here.

[K. L. McReynolds]

The 2&1/2 pitch rule(and that is a rule for asphalt shingles) is because of rain and water wicking. Rain water will wick under the edges of shingles at 2&1/3 pitch.

If the leanto section were to start at the roof edge of the shed(about 8' high?), why not use a membrane for the roof and pitch the roof just enough for water to run off(about 7' 10")

[srv52761]

mpwedge said:

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I'm in the Willamette Valley in oregon between Salem and Portland, we do get rain and occasionally snow, but I haven't seen more than 12" at one time over the 20 years that we've here.

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I wouldn't expect ice dams to be an issue in an unheated shed in your location. You need to be concerned about wind driven rain.

Generally I consider anything less than 3/12 a "flat roof". You can get roofing material that will match your shingles.

But then again...
I would expect most of the wind driven rain to be from the west. If your roof will be facing east, and is shielded from wind by your other building, and it is just storage yard stuff (and who cares if it gets damp once every couple of years or so), and you were willing to decrease the exposure; ...you could talk me into shingles.... (reshingle in 10-15 years instead of 25 on a flat roof that small would not be a big deal, and might be worth it to match the rest of the roofs.)

[mpwedge]

K. L, McReynolds said:

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The 2&1/2 pitch rule(and that is a rule for asphalt shingles) is because of rain and water wicking. Rain water will wick under the edges of shingles at 2&1/3 pitch.

If the leanto section were to start at the roof edge of the shed(about 8' high?), why not use a membrane for the roof and pitch the roof just enough for water to run off(about 7' 10")

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I was considering using a Ice and Water Shield membrane from Grace and cover the edges with a drip edge/cap, would that be enough?
Regarding the membrane, is that in place of any shingles?

[Steve Friedman]

I just used the GAF Liberty product on a small (6' x 12') low slope shed roof. My slope was a little over 1:12. The product (and others like it) are two layers. The membrane goes down onto the sheathing, then the drip edge, then a top layer that comes in 1 meter rolls - also adhesive backed, but has the rough texture of a shingle. It's only been a couple of months, but it's keeping the rain out. I'll let you know about the snow issue in around 6 months.

It's around $200 for enough product to do 100 sq. ft., so not cheap, but everything I read and everyone I talked to said not to use regular shingles below the minimum slope recommendation.

If you're OK with 2:12, you may want to consider a metal roof. I needed to keep the slope lower, but think the metal is a nicer look.

Steve

[CLETUS]

Mine is 3/12, steel, uninsulated. We get more snow than you, you should be fine with 2/12.

[K. L. McReynolds]

EPDM roofing

[Splinter Puller]

to answer your questions without excess preaching, I had a lean too roof once at 2-1/2" in 12" it did not leak. I doubled the tar paper. I did get a leak where the 5:12 met the 2-1/2:12 though and had to go back and add ice and water shield for about 4 feet above and below the transition. The low sloped roof faced south also.

As far as snow, this condition will be a place for drifts to form so you might have an issue with collapse or the need to shovel off the snow. If your building the entire structure don't do the shallow slope... do it right. If the existing 7/12 is there already can you raise this portion so your lean-too is above 3/12?

[mpwedge]

Here is the basic idea of what I'm planning... The lean-to will be used by my boys for working on their cars, so we're trying to get the max height in order to open the hood, etc. The shed itself needs to be no more than 200sq.ft. and the lean to can't be more than that either.
The lead to is facing north and the shed is behind the house and we're tucked behind hill too, so it does;t really get too windy.

[Splinter Puller]

Build the shed taller = lean-to roof can be steeper.