It is generally understood that unrestricted snow and ice cascading off of an elevated surface can be a dangerous situation. However, when we install snow management systems to protect us from these dangerous conditions, we tend to forget that there is a mass of snow and ice resting atop our roofs. Snow guards are designed to restrict this snow mass from exiting the roof surface in large amounts. However, there are times when a snow guard system does not perform as anticipated. For example, Improper installation, not having the appropriate amount of snow guards installed, unprotected roof surfaces above a protected roof surface (I.E. Solar arrays), or maybe the product was the wrong choice for your geographical region. Roof pitch and roof condition can also contribute to the problem.
On a recent project in New Jersey, a church had their snow retention system ripped out of their roof this winter because of sliding snow. They contacted us here at Alpine to see if we could diagnose the problem. Upon receiving images, it was apparent that a solar array was installed above a previously existing roof mounted snow guard system. (An unprotected roof surface above a protected roof surface as mentioned above.)
As we have mentioned in the previous blog, (https://fromridgetoeave.com/introducing-solar-snowdog/) solar arrays are considered a “Slippery Surface”. This means that when the snow accumulates on top of the panels and begins to melt, the water layer between the snow and the panel creates a frictionless surface; allowing the snow mass to slide off like an avalanche. This causes problems for anything beneath the array due to the lack of controlled movement. The snow simply evacuates the panel, and the large mass comes crashing to the ground.
On top of the church is a large array of solar panels; 34 panels in total, stretching four panels high from ridge, to near the eave edge. The original roof installer did take precautions and installed two rows of a three-pipe snow retention system, salvaged from the existing roof, below the array near the eave edge. The problem they are having is that they did not account for the snow mass to be on the move when it struck the guards.
For example, let’s assume that the solar panels are 39” x 65” (17.6 sq. ft.) each and they received the 50-year snow load of 25psf. This translates to 34 panels x 17.6 sq. ft. per panel x 25psf snow load = 14,964 pounds of snow on the array. When this mass of 14,964 pounds began to move, it is easy to imagine how that force could wreak havoc upon the guards below.
Sadly, there are competitors in the snow retention industry that advocate for the installation of roof mounted snow guards to be installed below solar arrays by themselves. For years Alpine has been transparent that this approach simply does not work. As you can see from the images of the church, using the roof mounted snow guards alone can result in damages to both the snow management system, and the roof itself.
On the church project, the snow accumulated on the panels over time but all at once slid off the panels, crashing into the snow guards below and dislodged them from the roof. This is referred to as “dynamic-load”. Most roof mounted systems are not designed to accommodate dynamic loads. HERES WHERE WE COME IN!
Alpine SnowGuards offers several supplemental solar snow management systems to help with this issue. This means that by installing our solar snow pad across the middle of the array, with the 2” SnowMax Lite Bar at the leading edge; the snow atop the church would have migrated off the array in a slower, more manageable fashion. This also mitigates the chance of damage to the roof – mounted system below the array.
Alpine Snowguards also offers the Solar Snow Guard 313 roof mounted system for the eave edge of the roof, similar to what the church had previously installed. However, the SSG-313 is used in conjunction with the Solar Snow Pad’s and the SnowMax Lite Bar, this helps to mitigate snow sliding from the array. Unfortunately for the church, they now have some roof maintenance for the summer. Hopefully, while they are up there, they take the time to install Alpine SnowGuards solar snow management systems so they do not deal with this issue again!
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Thank you for reading, tune in next time for more snow retention information!