When determining where to place snow retention rows, the first thing you want to ask yourself is “how much snow do you really want to fall off the roof?” The Metal Construction Association has a document to help you answer these questions. “Metal Roof Design for Cold Climates” lays out important processes of thawing and densification on rooftops for consideration. Pages 10 and 11 focus specifically on where to place the first row of a snow retention system. In this document, you will find the recommendation: “The first row of units or cross-members should be located close to (within 12 inches of) the eave end of the panels.” The document continues to explain…”this is because at some point, the snow bank that envelopes the snowguard will shear at the approximate location of the guard, and whatever portion of the bank is below the guard may fall from the roof.” Figure 11 does a great job of explaining the reasoning behind placing snow retention products near the eave.
You may find several different recommendations from other sources on this topic however, the MCA is a trustworthy source, which is why we have cited them. We recommend using this document or contacting an expert if you are in need of help. “Metal Roof Design for Cold Climates” also answers a number of other questions you may find yourself asking about your metal roof system application.
Now that you have an understanding of where to place your first row of snow retention system, it’s time to start thinking about the second row. Some calculations may reveal that you do not need a second row, but it is still worth looking into and double checking the need for a second row. A situation in which a second row would be needed is if/when your roof experiences heavy blankets of snow. Blankets of snow are dense, wet and not solidified which means they are more likely to undergo compression buckling. When compression buckling occurs, it pushes a “loop” upward from the roof surface and the heavy mass of snow compresses towards the eave. This is what causes avalanching snow off of a roof. Adding rows of snow retention systems will help stop the snow in its tracks. For more information on this topic, see Buckling of Snow.
Both articles used in this post are sourced from Metal Construction Association. Additional questions can be addressed on their website (www.metalconstruction.org ). You can also contact our team with any further questions.