Rob Haddock, CEO and Founder of S-5!
Each year, there are numerous incidents of accumulated snow unexpectedly sliding off metal roofs, causing hundreds of millions of dollars in property damage, personal injury and even death. Also known as a rooftop avalanche, it takes just a matter of seconds for this snowpack to suddenly release and dump tons of snow below the eaves.
The best way to mitigate this danger is by installing a scientifically tested and engineered snow retention system specific to the snow loads expected on your particular roof and metal roof profile.
System Design
There are two different approaches to restraining snow on your metal roof. One utilizes continuous horizontal components, assembled laterally across the roof commonly known as snow bars or snow fences. Such assemblies are usually installed at or near the eaves. Depending on specific job conditions and load-to-failure characteristics of the devices, they may also be repeated in parallel rows up the slope of the roof, but with a greater concentration near the eave area.
The other design consists of individual discontinuous parts known as snow stops or cleats, generally spot-located at or near the eave or repeated in a pattern progressing up the slope of the roof, again with a greater concentration near the eaves. This style also relies upon the shear strength within a snowbank to “bridge” between the individual units.
Both approaches increase friction between the metal roof and snow, but not all snow retention products and methods of attachment are created equal, Some are highly unreliable and can damage your roof—even in the absence of snow.
A “fence” (continuous) type snow guard; A “cleat” (discontinuous) type snow guard
Snow Retention Techniques
Let’s review the three techniques for mounting these two types of snow retention systems to a metal roof.
Two of the three techniques use mechanically-attached snow guards. The distinction between these two involves clamping, which grips the standing seam in some fashion without puncturing the panel material (non-penetrating) vs. fastening screws through the roof material (penetrating) into the structure (also a mechanical attachment). The third uses a chemically-attached “stick-on” adhesion method, which involves gluing individual snow guards to a roof surface.
1) Clamping a Snow Guard to a Standing Seam Type Roof
This method uses a seam-clamping attachment and is a measurably secure option for a standing seam metal roof profile. Clamps attach directly to the roof seam using setscrews that do not penetrate the roof (mechanically attached).
At S-5!, our clamping products use polished, round-point setscrews that compress the seam material against the opposite wall of the clamp – dimpling the material, but not penetrating it – and without coating damage.
Mechanical clamp attachment with round point setscrews is advocated by MCA, MBMA and USDOD
Clamp-to-seam attachments can easily be mounted after the roof has been installed and will not fatigue due to thermal heating or cooling of the roof. These measures prevent potentially voiding the warranties of a long-life, premium roof.
What You Can Expect With Clamp Mounted Attachments
With this method, the sliding force of the snow is transferred to the clamp and then into the roof panels. These loads vary from job to job. The holding strength of such a system should be quantified through rigorous testing and proven to resist the loads on any given job. At S-5!, we have tested and re-tested our clamps with almost every metal roof profile (more than 500 of them). You can view these results at www.S-5.com under the “Load Test Results” tab.
2) Attaching to the Building Structure Itself
The second method for mounting snow retention is a system that attaches snow guards through the roof and into the building structure (also a mechanical attachment).
Attaching to the building structure provides a secure and reliable method if properly tested, designed, installed and waterproofed.
It is only suitable for a roof that is attached the same way (i.e. with screws that penetrate the roof’s surface, attaching it to the structure).
Mechanical bracket attachment (for face-fastened roofs only) can also work successfully when tested and engineered correctly. This one wasn’t.
What You Can Expect With Structure Attachments
Snow guards that attach directly to the structure, require penetration for anchorage of snow guard brackets. With these devices, weatherproofing for the long-term service life of the roof is of paramount importance, or you run the risk of leaks. Such waterproofing requires a high degree of expertise in part design, sealant chemistry, selection/sourcing, etc.
With S-5! components, we eliminate the guesswork by providing a state-of-the-art system with factory-applied sealants–designed to last the life of the roof–including protection from UV exposure and over-compression of the seal. At S-5!, we test for leak-free performance in accordance to ASTM E 2140.
The strength of the structural attachment mounting method is also important and should be proven and matched to the in-service loads to which the snow guard will be exposed. S-5! provides web-based tools, enabling you to calculate your service loads quickly and easily. And, these proven holding strengths determine snow guard population to the specifics of your project scientifically—not by guesswork.
3) Using a Stick-On Guard
The third type of snow retention is a stick-on (adhered) part (chemical attachment). Some variations employ a factory-applied adhesive and others a field-applied one. At a glance, stick-on snow guard systems appear to be a very convenient and a lower cost option, but they are only lower in cost when you consider part costs vs. total project costs, including labor and quantities required to do the job. Moreover, the replacement costs over the life of the roof are extensive.
This is not “if”, but “when” the adhesive diminishes in holding strength. Adhesives all diminish in holding strength, beginning with the first day of exposure. Replacement time is often relatively soon after installation, depending on orientation to the sun and other environmental factors.
Adhesives diminish in holding capacity over time when exposed on a roof. There are 3 generations seen on this roof which was 8 years old at the time of this photo.
What You Can Expect With Chemically-Attached, Stick-on Mounted Attachments
Installation is simple enough. These parts attach directly to the roof with a glued application. But, if you look closely at the detailed instructions, installation becomes a bit more complicated— careful surface preparation is required, as well as many days of curing time for some at specific temperatures. (Suddenly, this is not as simple as it first seemed).
When installed, stick-on snow guards typically have the lowest holding strength (which continues to diminish with age). When they fail, they can rip away paint coatings, leading to corrosion. They also have the shortest lifespan due to the glue and/or plastic parts being unable to handle the harsh elements and total exposure expected on many roofs (i.e., UV, moisture and temperature change, etc.) S-5! has never and would never sell such a device. Industry trade groups, such as the MCA, MBMA and USACOE all strongly advise against the use of adhered snow guards.
The adhesive bond is to paint. If the adhesive does not fail, the paint may fail, leading to corrosion.
Main Take Away
A smart and rather low-cost investment in a snow retention system specific to your metal roof profile not only protects the roof and roof elements but protects the rest of the building and its occupants in addition to pedestrians, vehicles, equipment and landscaping below. It reduces short-term and long-term maintenance costs and most of all, reduces potential liability for building owners, designers and contractors. For information, videos and webinars on this topic and more, please visit https://www.s-5.com/ or www.metalconstruction.org.
About the Author
Rob Haddock, the inventor of metal roof attachment solutions, is a former contractor, award-winning roof-forensics expert, author, lecturer and building envelope scientist. He has worked in various aspects of metal roofing for nearly five decades.
