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Community and Q&A

Snow Slides With Metal Shed Roof

sfortier | Posted in General Questions on

Hi, I built a new house with a shed metal roof, black, with a 1.5/12 slope facing North. Screws are exposed. I live in Zone 6-7 (near Quebec City). Does this type of roof a potential snow/ice hazard, wondering if I should be putting snow guards at least over the door entrance. The attic is very air tight with R-65 insulation and about 20 inches of ventilation above cellulose.

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  1. jackofalltrades777 | | #1

    With that type of pitch on a metal roof, you won't get a dangerous snow slide like you would with a 5:12 or steeper pitch. The snow and ice will begin to hang over the edge but it will not be a hazard like on a steep roof. You will probably need to help it fall/break off with a wood broom handle or something.

    I'm surprised they would allow a 1.5:12 pitch roof in that climate zone. Online it shows 150" of snow annually which is pretty intense. What are you roof snow loads like?

    You will definitely get a lot of snow build up on that roof. Hopefully you won't have to start shoveling the roof if the loads get insane with snow. As far as dangerous run offs, you have nothing to worry about with that pitch.

    What made you choose exposed fasteners vs concealed fasteners? The latter will always be more leak proof.

  2. sfortier | | #2

    I'm located one hour south of Quebec City, the snow load used by the trust company is 2.8 kPa(1/50) or 58.5 Lbs/ft2. Frankly, I'm a little worried about that also, I contacted the engineer there and she basically told me the roof can easily handle over 3 feet of snow at 19 lbs/ft3.

    For the exposed fasteners, it was just that the local metal roofing manufacture (which happens to be my 3rd neighbor so was not really going to buy from elsewhere...) did not offer concealed fasteners, ended up putting a $2000 waterprrofing membrane under so it does not leak :-)

    Thanks Peter for the useful info on snow sliding, I think I will monitor the roof this winter and not install snow guards after all.

  3. Expert Member
    BILL WICHERS | | #3

    If you're concerned, it won't hurt anything to put extra guards -- it's just an additional cost. The same goes for a truss, you can request a truss be built for a heavier snow load if you want, it will just make the truss cost more. In situations like this, I think it's worth spending a little extra to feel safe in your home.


  4. PBP1 | | #4

    I have a 2:12 pitch (Montana) and have a breaker on the second floor roof, which is above the entrance to a two car garage. The breaker makes sure nothing more than 18" (maybe less) comes off at a time (usually not curled ice as on first floor). I wanted to make sure potential damage to cars is minimized. As to the first floor, without breakers, it usually curls, gets icy and falls in no more than one to two foot chunks but I have seen bigger slides. The hanging curls can impact the location of the drip line, which may effect landscaping (if you have things aligned with the regular drip line location). I wanted 1.5:12 but settled on 2:12, which resulted in higher ceilings and more volume, which I preferred not to have.

    1. ketchgould | | #6

      I am trying to decide on the pitch for my roof in Northern Wisconsin. I also want a 1.5/12 pitch but am worried about snow load. Does the 2/12 roof you have shed snow efficiently?

      Also, how did you vent the roof? I was planning on using I-joists and installing house wrap below the top flange on the I-joist and then filling with cellulose. The vent would be from the top of the I joist.

  5. dfvellone | | #5

    Exposed fasteners are less of a concern on a low pitch metal roof than the lap joint in the panels, which is where you're more likely to get water intrusion. It's a good idea to install a layer of butyl tape over the top of the bottom rib of each lap joint before the adjacent panel gets installed.

  6. plumb_bob | | #7

    I have seen many snow stops bent flat or torn out by the pressure of sliding snow and ice, do your research and get a system that can handle the heavy snow load for your area.
    To my knowledge not many metal roofs are rated for low slope application, except for some standing seam systems.
    As a side note, it is best to really think through how you want the snow and ice to come off your roof. Design so that it does not happen at entrances and walkways, and think of how much shoveling of compacted snow you want to do.
    A lady in my town got crushed by snow coming off the roof and had severe injuries.

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