snow loads/roof pitch and multi-levels

Guest User
Dear MRA Experts, Thank you for any advice you can give about choosing the appropriate metal roof for our design. The University of Wisconsin - Extension Housing Specialist, John Merrill, recommended I contact you folks with my question. Our plan is designed by a licensed architect, but I am just a regular old person so forgive me if I overdescribe things here. Our basic roof design is a central gable over two stories, with a 10" slope (10 ' rise, 12' run) which in turn would shed snow and rain down a 4' drop onto two parallel shed-style roofs of 3.75" slope (3.75' rise, 12' run). Basically, a tall steep-pitched roof that bottoms out on two shallow-pitched roofs on either side. Our original plan was to have the slick metal panels (standing seam) so the bottom roof can shed snow from the upper easily and prevent snow and ice buildup on either roof. We and our architect are concerned about the effect the impact of the snow load from above may have on the roof below, firstly with respect to structural damage to the metal, secondly with respect to appearance (dents, etc.) which could later lead to rust/other problems. Is there concern for this, and if so a design solution? Should we be looking into a different type of metal roof? Instead of encouraging the snow to shed, should we be slowing it down from above with those little spikes, or should we just switch to a whole different style of metal roof that might allow snow buildup (our snow loads here in northern Wisconsin can be heavy or moderate)? Then the question arises whether we even need to shed the snow, maybe the snow buildup would be beneficial for insulation purposes. Also, are we asking for trouble from splash-back of rain from the second roof if we don't put gutters on? They tend to get torn off by the snow up here. The roof edge is 2 horizontal feet from the side of the house. Sorry about all the questions, but we are hopeful you can help - we'd really like a metal roof from the standpoint of durability and looks with our design. What do you think? I would be happy to talk on the phone, or fax a copy of the roof layout if you like. Grateful for your prompt response, Leah Eder home phone (715) 373-1030 home fax (715) 373-1075 email [email protected]
Allan Reid
Dura-Loc Roofing Systems, Inc.
Good questions. First if one builds the home correctly, there will be no heat loss to cause ice damming. That means an interior air barrier, proper insulation, ventilation, moisture barrier and roofing material. You will still be subject to ice formation from the sun on occassion if the roof has an attic as at times the overhang will be cooler and in the late afternoon any melted snow could form drip icicles. Colour of the roof material has a bearing here as well as its energy properties. If you choose a smooth finish metal roof, you will get snow shedding. There are a number of snow gurads available and typically each roofing material has recommendations as the style and fastening vary by roof pitch, snow load and roofing material, so be sure to consult the manufacturer. With a 10/12 pitch it will need to be substantial.If you were using smooth metal, I would choose a system that rests on the deck and order it in a heavier gage to resist dents. Alternately you could choose a granular roof system like we manufacture. It reacts the same as an ashphalt shingle roof holding the snow. As well it slows the speed of water run off down. With any metal roof ensure that if gutters are used, that the top of the outer trough is below the roof plain so that any snow will slide over. They also make strap hangers to strap the gutters on and one can use more clips. If you still have ice concerns then add in a heater cable, however build the sassembly right and there should be no concerns. Like you though, I feel gutters are a maintenance item and when I constructed my house I left 95% of them off and I have the same upper roof shedding onto a lower roof. For the lower roof , I would recommend trying to get the pitch revised to 4/12 if possible. If the roofs are over an unheated area there stands a chance that the melting snow from above could freeze and build up on the lower roof. If the lower roof is over a heated space then you will challenges making sure it is vented along the wall and that the snow does not cover the vents The width of the upper roof will have a factor here. Other things to consider is using an ice and water shield over the lower deck and the length of the upper rafter as the upper roof area determines how much rain and snow it needs to shed. As well the orientation of the home and roof. Does the ridge run East West so that one face is south? Does it have dormers? Is the roof assembly constructed with an attic or as a vaulted ceiling? I hope this answers more questions than I left you with. If you have more detailed questions please feel free to contact me directly of fax a roof plan through to 519-688-2201 and we will be able to make more concrete suggestions. Good Luck and thanks for taking the time to study and plan your new roof system.
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