Snow guard design considerations

Bar or fence- styled snow guards can be attached to standing-seam roofs with clamps or attached to exposed, fastened roofs via screws.
Bar or fence-styled snow guards can be attached to standing-seam roofs with clamps or attached to exposed, fastened roofs via screws.

Snow guards typically come with a limited manufacturer warranty of between three and 25 years. However, design, engineering, and installation determine if the snow guard is going to fail or not. A snow guard can be designed properly and approved by an engineer, but it would not matter if installation is incorrect.

It is recommended to work with a company specializing in snow guards before the project goes out to tender or before final budgets are calculated. These companies can provide snow load calculations specific to the project’s location and roof’s geometry. They have an understanding of the factors affecting snow loads, such as snow pileup or drift due to adjacent roofs or parapet walls, upper roofs shedding snow down to lower roofs, and how dormers and valleys can affect snow accumulation, and will be able to recommend the proper number of snow guard row(s) required as well as snow guard layout. This initial work not only assists with proper budgeting, but also eliminates guess work for contractors or surprises that may arise when more rows of snow guards that initially planned are required.

Another factor to consider when budgeting for snow guards is that cheaper is rarely better. There is a tendency in the industry to supply snow guards made from bent sheet metal formed into a triangular shape that are either screwed to the standing seam or screwed through the rib of the panel down to the underlayment, which is, in most cases, plywood. These types of snow guards rely on the strength of sheet metal screws to resist hundreds of kilograms of snow and ice sliding down the roof. However, the screws and sheet metal ribs are not designed for that. The sheet metal screws are employed to secure a metal roof to wood or purlins. The initial cheaper solution will cost the client more money to repair. If the snow guard must be screwed through the metal roof, it is important to install wood blocking between rafters where possible and secure the snow guard to the wood blocking. Again, it is important to do load calculations to determine if one or multiple rows are required.

Cleats or pad style

These are individual or unitized parts that are secured to the standing seam, screwed through the roof or adhered to it. These types of snow guards are used in low snow load areas or for esthetic reasons. The drawback to these snow guards is their holding strength tends to be low and require multiple rows along the whole roof. Adhesive snow guards rely on an adhesive to secure the snow guard to the roof. The problem with these is they can only be installed during warmer months. The adhesive must have proper conditions for it to cure and, usually, require multiple call backs to replace them. Further, adhesives break down due to exposure and weaken over time, resulting in failure.

Bars or fences

Commonly referred to as pipe or rail-type snow guards, they are designed to provide a continuous wall in which the shedding snow will impact. These types of snow guards can be attached to standing-seam roofs via clamps or attached to exposed fastened roofs via screws. The bar or fence-styled snow guard is most commonly used across Canada and can be less expensive than the cleats or pad styles.

The taller the snow guard the better

A deeper snowpack does not equal a taller snow guard. A taller snow guard is not any more effective than a shorter one because the snow does not slide from the top. The sudden release of the snowpack happens along the roof panel at the base of the snowpack when the frictional bond between the snowpack and roof panel has been reduced. It is the base of the snowpack that must be restrained, and not the top.

Choosing a snow guard

When choosing a snow guard, ask the manufacturer about product testing. As mentioned earlier, clarify if the snow guard is designed around the ultimate load or failure point or around an allowable load. It is important to remember the snow guard is going to be the one piece of equipment that will stop the snow from falling off the roof with potentially disastrous outcomes to the building.

David Kowch is the business development manager, overseeing all operations at Sky Products. Kowch has over 15 years of business, project, and client management experience. Kowch can be reached at davek@skyproducts.ca.

Control the content you see on ConstructionCanada.net! Learn More.
Leave a Comment

Comments

Your email address will not be published.