What Type to use, How and Where to install them correctly
The buildup of snow and ice on a pitched metal roof causes challenges in many areas around the country. The collection of snow on a roof can produce significant sliding forces, which can cause the snow to fall suddenly. Snow retention systems reduce the risk of sudden rooftop avalanches and mitigate the hazards present in the area below the eaves.
Snow guards come in a variety of shapes and sizes. There are discontinuous snow guards, and continuous snow guards.
Snow cleats or pad style snow guards (like our Snow Yeti) are normally used in a redundant fashion, relying on the “bridging” of a snowpack to span between adjacent devices to limit snow build up.
Continuous snow guards are otherwise known as rail type snow guards, snow fence, snow rail or pipe-style snow guard. These can be single or multi components: brackets or seam clamps that are attached to the roof, and cross-members that are anchored to the brackets or clamps that restrain the sliding snow. Continuous snow guards can be made up of one or multiple cross-members.
Choosing the right type of snow guard is a decision largely based on aesthetic and personal preference. Either type can work—continuous rail or discontinuous cleat-type systems—provided that either is appropriately tested, correctly installed and proven by engineered calculation to resist the in-service loads presented on a site-specific basis.
The panel type and material, roof size, local snow loads and aesthetics are some other issues to consider.”
Snow guards are considered a life/safety product, and therefore should have the service life and durability equivalent to the roof itself.
Because metal roofs have exhibited service lives of more than 60 years in documented field studies by the Metal Construction Association (MCA), this requirement should rule out the use of plastics (polycarbonates) as they do not measure up to such a service life in outdoor exposure.
In order to color match the roof material, it is recommended that the type of paint or powder coating is equivalent to the roof material in terms of fade and chalk characteristics. Lesser quality paint finishes on the snow guards will fade more rapidly than the roof, producing a very unsightly mismatch within a few years.
Snow guards should always be placed at the lower half of the roof plane. And, depending on the system, snow guards can be placed in a single line, or in multiple rows.
Generally speaking, if installing one row and using a continuous rail-type system, your snow retention would be installed approximately 1 to 2 feet from the eave. Current code suggests 18″ inside the building envelope (ex. If your overhang is 1′ then the first row of snow guard should be at approximately 2.5′ from the eave) as this is most likely where heat will escape due to poor insulation, causing ice damming and snow build up. The majority of the snow load is carried on the bottom half of the roof due to heat loss, wind, sun exposure and gravity.
Exact placement of snow guards is a mixture of art and science. In general, snow accumulates on a roof with greater concentration near the eaves and valleys due to wind scouring. All snow guard devices rely upon the compressive strength of a bank of snow to resist its downward migration. The compressive strength of snow increases as it compacts from its own weight, increasing its density. This results with the greatest compressive strength of the snow bank at its base (adjacent to the roof surface) and at its downslope (eave) end. For this reason, the snow bank’s downslope extremity is the best place to interface with snow guards.
Additionally, slope is a critical component in the engineering/design of snow retention because steep slopes combined with long panel lengths are two of the factors that help determine if multiple rows of snow retention are needed.
When installing snow guards, always refer to the manufacturer’s instructions. Since snow guards are expected to last the entire service life of the roof, we recommend always using mechanically attached snow guards, never glued. Relying on caulk/adhesive for attachment is not the preferred method, whereas using a mechanically fastened clamp/rail combo is the stronger alternative.
The method of attachment of snow guards should be consistent with the roof type. Therefore, a face-fastened roof should use a face-fastened snow guard attachment with butyl copolymer sealants and fasteners of no less quality than those used for the roof itself. And, a standing seam roof should use clamp-to-seam attachments that are metallurgically compatible with the roof material.
For through-fastened roofs, sealants should be at least equal in performance to those used in the roof itself. In most cases, this means using high-quality butyl copolymer tapes and part designs that protect the sealant from UV exposure and over-compression – such as dome style fasteners. Similarly, fasteners should also last the life of the roof. Exposed fastener heads should be AlZn alloy or 300 series stainless steel, and washers should be black EPDM.
According to the MCA technical bulletin, sealants and washers can be used to protect the sealing material from direct exposure to sunlight. When choosing washers or sealants for waterproofing, use ones with the same chemistry as the washers and sealants present in the roof system to ensure a similar expected service life. Preferred sealants are isobutylene/isoprene (butyl) polymers or materials with similar of greater service life, while ethylene propylene diene monomer (EPDM) or similar materials are the preferred washer chemistry, using carbon black UV stabilizers.
It is important that the snow guard system is designed for each specific project. The steeper the roof, the greater the forces are that act on the snow guard assembly. For example, a 4:12 roof that is 50 feet from eave to ridge with a 40-psf design roof snow load will exert 633 pounds per linear foot of eave on the snow guard assembly. If the slope of the same roof is changed to 7:12, the force changes to 1,008 pounds per linear foot.
For installing snow guards, most of the tools needed are common to the trade.
When deciding on the right type of snow retention system, be sure the design is adequate and specific to your application and location.
Technical Resources from the Metal Construction Association:
- Qualifying Snow Retention Systems for Metal Roofing
- Metal Roof Design for Cold Climates
- Fastener Compatibility with Profiled Metal Roof and Wall Panels
For more information, visit www.metalconstruction.org/Tech-Resources