low slope question

Guest User
Hi. I'm an architect developing specifications for a 2-story 3,200 SF residence in Los Angeles. The house will be LEED Gold, and I've narrowed the spec down to a 2" mechanically-seamed metal roof by a local manufacturer. The design includes a series of shed roof sections with the longest length being 36 feet. Currently the slope is modeled at 5/8" per 12", a hair steeper than the manufacturer's minimum warrantied slope of 1/2" per 12" (the design will include an ice/snow shield underlayment). The roofing company rep told me that although they warranty 1/2" per 12" roofs, my 5/8" per 12" roof could still potentially pose water leakage problems and he recommended a minimum 1" per 12" design. For better or worse, I'm unable to alter the roof slope to that degree, as it would adversely affect the height and aesthetics of the project. However I might be able to get away with changing the minimum slope to 3/4" in 12." My question is, is it worth it for me to alter the slope by 1/8" per 12"? Or should I just concentrate on making sure that my contractor is very careful in achieving the 5/8" per 12" slope? As an aside, I was surprised that the rep thought a 5/8" per 12" slope would look "flat." In my drawings and model the slope looks gradual but certainly perceptible, esp. over its 30-foot-plus runs. I'd be curious to hear your opinions on that too. Thank you in advance for your feedback. Best, Amelia
Todd Miller
Isaiah Industries, Inc.
That sort of slope will show some pitch but the average person will see it and say the roof is flat I believe. Systems intended for it are used on those very low pitches all of the time. A lot too, depends upon not having anything to the geometry of the roof that impedes water flow or causes certain panels in the roof system to carry inordinate amounts of water. Ultimately, adding some to the pitch helps allow for any potential errors which may be made but chances are that a system that leaks at 5/8:12 will also leak at 3/4:12. Thanks!
Eric Novotny
An informed customer is the Best Customer!
What architecture firm? I have a friend who works in LA who works and an urban planner. The ability to accommodate that low a slope is completely dependent on the seam type and the manufacturers guidelines. That being said, we have installed mechanically seamed roofs on 0:12 roofs without issue. +1 to Todd's point as well. If it leaks at 5/8:12, it will probably lead at a 1:12 too. Ice/water under the entire roof deck is unnecessary and wasteful in my opinion. You will get just as good a performance with a synthetic underlayment (don't both with breathable stuff just standard poly ones are fine). I am not sure how LEED views ice/water but it is a band-aid for a poorly designed or vented roof system. If you are going to use it, make sure it is non-granulated.
Dick Bus
A 2" tall mechanically fastened metal panel on a 5/8 in 12 slope in the LA area will work just fine with the proper underlayment. Keep the penetrations to a minimum, between the seams and allow for proper drainage around them. Another recommendation is to work with manufacturers that are a part of the Metal Roofing Alliance or the Metal Construction Association as they all agree to produce and promote quality products using the appropriate coatings and pretreatments. let us know if we can help further.

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