Calculating Snow Shedding / Friction Coefficient

Guest User
I'm planning on building in a high snowload location. The site parcel report indicates it will require designing for a 316 psf snowload. Windload requirements are more moderate (70 mph). Seems like the optimal roof would be one that sheds snow rather than retaining it. Ie, a higher pitch roof is called for. Are there rules of thumb, or more complex calculations for knowing when a roof would shed based on pitch, roof surface/finish, and perhaps interior insulation ? Are there standards for discounting snowload based on roof pitch and/or finish. Are there specific product choices that address this such as ways to select a slicker roof surface ?
Allan Reid
Dura-Loc Roofing Systems, Inc.
Certainly talk to the local building department as they have a good hditory. What you will find is that truss design to meet the loading will drive it too and I suspect that you should be 8/12 or greater on roof slope. Certaily granular finishes hold the snow more than smooth finishes. Whether the snow stays on or not you are designing for that load but certainly shedding it off is wise. Also wise to ensure you build it so there is no heat loss and ice daming potential.
Guest User
Thanks for the suggestions. I started this out by looking at particular kit home that uses a fairly shallow pitch (4/12) which is why I started thinking about it. I believe I worked out the math with regard to tranlating vertical load (snow weight) into a force perpenticular to the roof line (namely snowload * cosine(roof pitch in degrees)). However I'm still focused on understanding the frictional component. I've found the formulas for calculating the frictional force, based on snowload, pitch, and the frictional coefficient - what I lack is the actual frictional coeffecient for types of roof and snow. Would any metal roof manufacturers publish such information ?
Todd Miller
Classic Products, Inc.
I would guess that it has never been studied.
Guest User
I would think you could use the friction coefficient of the metal or of the finish. That might be available somewhere. Ask an engineering professor - they teach materials science.
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