Snow Guard Science

The manufacture of snow retention systems is a completely unregulated industry.

Would you be safe standing under that roof?

By Rob Haddock

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There are no snow guard police to ensure that only engineered products are released to the market. Rooftop avalanches are a life-safety issue. Every year, cars are crushed and people are injured or killed from snow slides. Often by default, the contractor becomes the ultimate decision maker and may be assuming liability when it comes to the selection of under-designed, untested systems.

In 2016, the tragic death of a 2-year-old girl occurred after seven feet of snow tumbled off a cabin roof in Idaho. A deadly rooftop avalanche took a mother and her son in 2018 near Lake Tahoe, Nev. In 2019, a woman in Wyoming and a man in Coloradowere both killed in roof avalanche disasters.

How does it happen? Avalanches have a scientific cause. When the temperature-sensitive bond between roof and snowbank breaks free, an avalanche occurs. As the roof warms (from UV rays or building heat loss), it melts the interface bond. This melt-water lubricates the slide. Snow guards can prevent the slide by restraining the bank of snow, but only if properly designed and engineered. The forces of sliding snow vary with job specifics but can be scientifically calculated for any given project. They are the forces that must be restrained by the snow guard system and should be proven adequate by its tested holding strength.

Liability of Installing Non-Engineered Systems

The market is inundated with snow stop systems for metal roofs, each claiming to be the first, best or some other superlative. If the contractor believes all of the sales hype without vetting, the pitfall is this: even if the product is installed according to the manufacturer’s instructions, but the system is under designed, it will fail, leaving the contractor holding a bagful of liability. Protecting yourself from this liability starts long before the product gets on the roof.

How can a contractor vet the products they install? Manufacturer transparency is at the heart of vetting a snow retention system. A vendor who lauds the capabilities of his system but fails to provide proof of those claims is blowing smoke. When selecting a snow guard solution, a contractor should scrutinize manufacturer qualifications and demand transparency to ensure a safe, engineered application and long-term service on every project. If the manufacturer has truly done his due diligence, he will be pleased that you ask him to prove it.

Tensile load testing. To resist the forces applied to any system, we need to know at what point the attachment fails. Then, we can calculate the required population and spacing of the attachment so that it doesn’t fail. This requires an enormous amount of testing, and the panel-specific results should be published on the vendor’s website for your inspection. If not, it probably does not exist.

Long-term performance. Can the vendor substantiate his track record over years of time and prove service/durability with interactive load testing tables? Ask for this evidence!

Warranties. Does the manufacturer offer a meaningful performance (not just material) warranty? Are you confident that they will be in business several years down the road to honor it? Ask for it prior to purchase—and read the fine print!

Engineering calculations. These must be provided by the vendor on a project-specific basis and should incorporate the tested strength of the device with an appropriate factor of safety applied. Insist these calculations be provided. If you don’t feel qualified to review the calculations have the vendor provide them stamped by a Registered Professional Engineer.

Experience. The vendor should show evidence of experience and the system’s track record. You cannot make a product perform better than its design. Has the vendor demonstrated sufficient expertise to do that?

Further vetting should include:

• Use of chemically and mechanically certified material—ask to see those certifications.

• Testing by a third-party A2LA accredited lab—ask to see the lab report specific to your roof profile and manufacturer.

• Following ASTM material standards—require a letter of compliance.

• Utilizing certified manufacturing processes and third-party audits in an ISO 9001-15 compliant facility—ask for a current copy of the ISO Certificate.

• Download the Metal Construction Association (MCA) technical bulletin, “Qualifying Snow Retention Systems for Metal Roofing.” This industry consensus document provides invaluable criteria for snow guard selection. At a minimum, ask your vendor to provide a written statement that their system fully complies with this document.

Protect Yourself and Your Customer

Remember: In the end, the vendor claims become your promises. Would you feel safe walking under that roof when it’s loaded with snow?

Rob Haddock is founder and CEO of S-5!, Colorado Springs, Colo. For more information, visit

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