Roof Material for Snow Conditions
Plans changed, and a really flat metal roof just isn’t practical.
The pitch has been changed to a 2:12, but I’m going to keep it non-snow-sliding.
The whole roof will have an ice and water shield underlayer.
I’ve been thinking torch on, but life expectancy seems to be in the 10-20 year range.
Is there anything better like EDPM that wont let snow slide?
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first separate the EPDM and ice and water, they don't play well together
I have EPDM on a 2:12 and prevent snow sliding by buying a number of walking pads, the kind with many cylindrical nubs sticking up. I cut them in thirds and bonded them to the roof edge. I also bonded a few in the center of the roof
snow does not slide
Just say no
Built-up roofing could be an option for you. Its probably the most common roofing material used on low-slope or "flat" roofs in New Mexico, typically done with bitumen asphalt and topped with layer of aggregate, like small gravel.
Why not use EPDM? It should last 20+ years, provides decent traction (though be careful in wet or icy weather) and a long history. I've never seen torch-down on a house. Installing EPDM never causes fires; can't say the same about torch-down.
As Keith says, though, Ice and Water Shield can't be used in contact with EPDM because the VOCs make the EPDM brittle. You might be able to use high-temp Ice and Water, which is butyl-based, not bituminous.
Many metal roofs can work on a 2/12 pitch, although they work better with a steeper one. The advantage over other alternatives is their longevity. Installing snow-guards will stop any sliding at that shallow a pitch.
I'm a fan of polyurethane roof membranes. You'd have to do something special to prevent snow sliding but shouldn't be a big deal. I have a green roof (live vegetative roof) on my current build and there is no snow sliding. Not suggesting this just adding to the story.
Flatroof or bust,
FWIW, I have mixed metal and membrane roofing. Thanks to the Santa Fe look my spouse wanted, we have 1.75 in 12 pitch on two roof planes and 2.5 in 12 over the garage . After much discussion about standing seam and the snow dam potential creating leaks on such a low pitch, we went with IB pvc membrane on the low slope roofs. IB offers a lifetime warranty. Metal went on the lower parts where the 4 in 12 was safe.
The snow pretty much sits where it falls on the low slope roofs. The deepest snow we have had yet was 24" . Some blows off in the winds, the rest slowly melts as the sun gets the parapet edges warmed up. The membrane doesn't move heat like the metal. Even late in spring when the snow is surviving in slushy islands, the snow doesn't slide anywhere.
I deliberately did not include snow brakes on the metal roof areas. I also skipped gutters on advice of local sources. The snow on the metal sections does slide and rolls off the edge in a curly wave. If you are curious, I have photos somewhere on my computer.
If none of your doors occur where snow or melt water would fall on guests, then consider letting the snow slide. The brakes can cause ice build up on metal roofs due to the sun effects. The snow on the metal roof always melts from wherever the sun gets to it. Most commonly the flashing first along the wall intersect. Doesn't matter how cold it is, water will start to slide under the snow pack and soon the sections created by the standing seams will begin advancing. The roof is R52 so the melting and ice is almost 100% sun driven.
I will see if I have some pictures of a typical late winter day of the membrane roofs and post later.