Specifying Snow Retention Systems

by Stacy Rinella | March 14, 2024 7:00 am

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Rooftop avalanches cause hundreds of millions of dollars in property damage, personal injury and even deaths each year—creating a life-safety issue and potential liability for designers. Proper, job-specific design of a qualified snow retention system dramatically reduces building owner/designer liability when sliding snow presents a hazard, but how does a designer discern prudent product selection from sales rhetoric?

While engineered snow retention systems complement the roof, the design and manufacture of such devices have been completely unregulated—until recently. For years, there were no industry standards or mandates for the design, manufacture, use, or testing of such devices—no “snow guard police.” Still, many applications are not specifically engineered for design loads, posing a threat to public safety. Historically, the only policing within this field has been done by the architect, specifier—and too often the contractor.

Designers need to know what steps they can take to protect them from potential liability and how best to vet these devices.

Liability

With the market inundated with metal roof attachment systems, often by default, the designer or contractor becomes the ultimate decision-maker, and both may assume liability when it comes to the selection of under-designed, untested systems. If the designer believes the sales hype without properly vetting the system or manufacturer, the pitfall is this: even if the product is installed according to the manufacturer’s instructions (but is under-designed), it may fail, leaving the designer liable. Protection from this liability starts long before the project is bid.

Science

The service loads applied to a snow guard system are a relatively simple calculation varying with site specifics known to the design team:

1. The design roof snow load
2. Roof slope
3. Roof (or rafter) length from eave to ridge

These three variables determine the force a system must resist for any slippery roof surface and should be included in plans and specifications requiring an engineered system.

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Testing

To resist the forces applied to any mounting system, the point at which the attachment fails must be known. Then, the required population and spacing of the attachment must be calculated so it cannot fail. Since the system may comprise multiple components, a “load chain” results. The calculated force is transmitted through this chain into the building structure. Each link must be proven by testing and/or engineering analysis. The weakest link determines the strength of the chain. Safety factors are applied to determine allowable structural capacity.

Vet and specify

Manufacturer transparency is at the heart of vetting a snow guard system. The designer should scrutinize manufacturer qualifications and certifications to ensure a safe, engineered application and long-term service. Transparency should extend from material sourcing through manufacture and handoff.

Proof of testing

Anchorage to the roof should be tested repeatedly. The connection strength of seam clamp-to-standing seam varies widely depending upon clamp design, type/gauge of roof material, seam geometry, dimensioning, and source. Testing should be conducted by a third-party ISO 17025-accredited lab. Testing must be specific to the profile and roof brand of the project—with test reports furnished during design and later with submittals, proving the anchorage values used in calculation. Panel-specific results should be published on the vendor’s website.

Proof of engineering

Project-specific engineering must be provided by the vendor on a project-specific basis and should incorporate the tested ultimate strength of the system with an appropriate factor of safety applied. Insist calculations are provided before product/system selection. Designers should require these calculations with submittals. Even better, require by specification that calculations be stamped by a registered professional engineer.

Proof of certified manufacturing

How can one know if the product tested is truly the product purchased? Systems may look the same, but metal alloys, tensile, yield, and other mechanical properties are verified through certified manufacturing with third-party audits in an ISO 9001-15 compliant facility, not by similar physical appearances. It is advisable to request to see the current ISO Certificate, ideally displayed on the vendor’s website.

Proof of adherence to the new industry standard

In the absence of building code that covers snow retention, a new industry consensus standard for testing and certifying snow retention devices has been established by the International Association of Plumbing and Mechanical Officials (IAPMO) titled Evaluation Criteria (EC) 029-2018, Standing Seam Metal Roof-Mounted Rail-Type Snow Retention Systems. An EC document from IAPMO is a consensus of professionals concerning the specifics of how a product or system is to be evaluated and how the results are interpreted and applied. It is considered “code equivalent” and may be used by specification to qualify proper design, testing and production. Require the vendor to provide a written statement of compliance with the IAPMO EC 029–2018 and/or the Metal Construction Association (MCA) white paper on “Qualifying Snow Retention Systems for Metal Roofing”[3], which also provides industry consensus.

 

Warranties

Verify the manufacturer offers a meaningful performance (not just material) warranty. Obtain a copy before specification—and read the fine print. Will they be in business for the long term to honor it if needed? Has the vendor substantiated its track record? The duration of the company’s operation is irrelevant. The question is: “How long has the system been in use?” Can the vendor demonstrate service/durability with interactive load-testing tables?

The bottom line

Mitigating liability starts before the bid. A lack of code mandates provide a free pass to unqualified systems.  System failure can threaten anything or anyone on the ground below, not to mention damage to the roof. A smart and rather low-cost investment in a snow retention system reduces potential liability for building owners and designers.

Rob Haddock, CEO and founder of S-5!, is a former contractor, award-winning roof forensics expert, author, lecturer, and building envelope scientist who has worked in various aspects of metal roofing for five decades. S-5! recently achieved an Evaluation Report of compliance (ER) to IAPMO EC 029–2018 industry standard for testing and certifying snow retention devices.

 

Source URL: https://www.metalarchitecture.com/articles/features/specifying-snow-retention-systems-2/

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