Have questions? Ask the experts.

Ask-The-Experts forum

Below is a forum for exchanging information concerning residential metal roofing, including general material and metal roofing installation questions. Should you have questions or concerns that deal with specific branded metal roof products please contact the manufacturer directly.


Log In

Ask-The-Experts >

Calculating Snow Shedding / Friction Coefficient
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 ?
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.
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 ?
I would guess that it has never been studied.
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.


This topic has been closed or locked. You can no longer post a reply.

If you have a metal roofing question, please post it above and a member of our panel of contributors will provide a response. Answers provided by contributors are based on the limited information posted and, therefore, may not provide a complete or accurate answer under all of the relevant facts and circumstances. No advice or information obtained through the forum or this website shall create any warranty by MRA or its contributors whatsoever and all warranties are disclaimed. MRA and its contributors disclaim any liability of any kind arising out of or relating to use of the answers or information provided hereunder, and by using the forum, you agree to waive any claims against MRA and its contributors and hold them harmless from any liability or damages of any kind arising out of or relating to the forum. For a detailed description of the terms and conditions of use of the Forum and this website, including a more detailed description of disclaimers of warranties and limitations of liability, please see the Terms and Conditions section of this website. MRA does not endorse or recommend any commercial products, processes, or services. The views and opinions of contributors to this Forum do not necessarily state or reflect those of MRA or its members, and they may not be used for advertising or product endorsement purposes.

  • Read industry related articles about metal roofing.
  • View all the types and styles of metal roofing
  • Locate a metal roofing contractor near your home
Find a contractor near your home