Snow guards and metal roofs 101

figure 11
Figure 11: Some modern snow guard attachment clamps attach with round-point non-penetrating screws, which do not harm the roof. Such products also fall within metal roof manufacturers’ warranties.

There is more than one fastener used with attachment devices for metal roofs and they need to be closely scrutinized to ensure they do not harm the roof and attach without voiding the metal roof manufacturers’ warranty. Many snow guard devices employ a mechanically attached fastener with a round, polished head that creates a ‘dimple’ in a standing seam. This acts as the active holding point of the fastener. The dimple is created by the round head of the fastener integrated with a ‘well’ in the snow guard clamp to accommodate the metal seam protrusion on the other side of the seam (Figure 11). The round point of the fastener is designed specifically to dimple the seam without penetrating it, and subsequently stay within the non-penetrating clause of the metal roof manufacturers’ warranty. The polish given to the round fastener head ensures the roof’s protective coating is intact, eliminating a place for metal corrosion to begin.

Other fasteners employ a cup-tip and are designed to ‘dig’ into the metal seam to create holding strength. This intrusion into the seam of the metal roof could potentially penetrate the seam of the metal roof and void the manufacturers’ warranty. The action of digging into the metal seam by the fastener also removes the roof’s protective coatings and exposes bare metal to the corrosive elements of the weather. This could potentially reduce the roof’s service-life. Cup-tip fasteners are not recommended in publications by Metal Building Manufacturer’s Association’s (MBMA’s) Metal Roofing Systems Design Manual section on fasteners, and the Metal Construction Association’s (MCA’s) Metal Construction Association Technical Bulletin.

To protect a metal roof so it may achieve its full useful life and maintain the manufacturer’s warranty, it is recommended to specify non-penetrating round-point fasteners in specification documents.

Performance issues
To maintain the metal roof manufacturers’ finish warranties, no chemical adhesive or sealant can be applied to the face of the panel. These chemical-based materials will not properly adhere to the metal roof surface and will damage the paint finish—subsequently invalidating the finish warranty.

figure 12
Figure 12: Adhesive attached components to modern metal roof finishes are not recommended by manufacturers due to bond failures, their short useful life, and violation of metal roof finish warranties.

Chemical sealants will weaken as they age because they are subjected to environmental factors such as hot and cold cycling, UV light exposure, and moisture—meaning they will not maintain a strong and measurable bond for snow guards. Ultimately, the vector force placed on a chemically adhered (i.e. adhesive applied) snow guard will cause the device to fail and break loose from the roof. This can be observed after a few years on most roofs employing adhesives as the attachments (Figure 12). The subsequent ‘scar’ created by the broken bond is both unsightly and could be a potential corrosion point in the future.

The science behind this inability to chemically adhere items to metal roof surfaces is simple. The polyvinylidene fluoride (PVDF) resins used in modern metal roof coatings are designed to be non-stick surfaces and resist substance accumulation. Consequently, an adhesive-applied snow guard is destined to have a high failure rate and will not provide long-term protection for people or property. Mechanically attached snow guards are the only solution for long-term peace of mind and preservation of roof manufacturers’ warranties.

Cost issues
It is imperative to understand the tested holding strength of the snow guards to be able to accurately plan a successful snow guard installation.

A mistake made when using snow guards involves cost issues—spending either too little or too much. At first glance, low unit prices make a small adhesively adhered parts seem like a bargain. However, the required holding strength of some parts are significantly lower than others, and they may be applied redundantly. Consequently, the cost of some ‘bargain’ parts is much higher because they may require more units per panel due to their low holding strength. The difference on a job could add up to thousands of dollars.

This is why it is important to compare not only costs, but also holding strength. In the case of snow guards, the greater the holding strength of the device, the fewer rows required in the system to hold the volume of the snow. Fewer parts impact both the initial product cost and the installation labour.

The penetration and fixity of the roof panels (roof warranty violations)
When applying anything to a metal roof, there are two cardinal rules that should never be broken—do not penetrate the roof panel, and do not fix or pin the panel in place to violate its ability to move by expansion and contraction.

This is clearly appropriate when planning snow retention devices. As a delegated design in specifications, it is imperative to prescribe these two cardinal rules to the subcontractor developing the ultimate design of the snow guards.

Snow guards with standing seam roof clamps and non-penetrating round point fasteners are specifically designed to protect the roof by attaching without penetration and allowing the roof to continue its thermal cycling. Installers need to take reasonable care during installation by following snow guard manufacturer installation instructions.

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3 comments on “Snow guards and metal roofs 101”

  1. There is definitely a duty of care to the public and visitors to a property if snow fall is likely. Otherwise there is no need to clear the roof unless the depth is ‘exceptional’.
    There is a cinema near us and the metal roof regularly deposits sheets of ice on to the pavement. But they don’t do anything about it.

  2. Thank you for this informative article, Harry. Can you also comment on the risks, if any, resulting from the retention of snow on the roof resulting from the use of snow guards? Assuming the snow guards do their job, retaining snow on the roof, the weight of snow will increase during the winter season. At what point would it be necessary to manually clear the snow from the roof in order not to exceed the roof’s weight bearing capacity?

  3. Roofs are designed to withstand a specific “Designed Roof Snow Load” based on the Building Code which should be used to design and snow guard for a roof. A properly designed snow guard system will take into account essential factors such as, pitch of the roof, the length of the panel or ridge to eave distance, the eave run or assembly length of the snow guard, the Designed Roof Snow Load, and the distance between standing seams. By using these factors you can anticipate the snow load sliding down the roof and how many rows of snow guards you may require, which if multiple rows of snow guards are required will break up the overall load into smaller loads across the roof – so to speak. In the end, the snow load will always be on the roof until the friction between the snow and roof is no longer present. This can happen when the temperature rises and causes the snow to melt along the panel which then reduces the friction, and therefore causes the snow to slide down the roof.

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