Opportunities for Designing a Roof for Snow Retention
by Richard K. Olson, president & technical director, Tile Roofing Industry Alliance
(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Industry Alliance. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at firstname.lastname@example.org.)
As a design professional, January provides an opportunity to reflect upon our needs and resources for the upcoming year. For me, I start with obtaining the latest codes, both national (ICC) and local for the areas I might encounter such as the Florida Building Code (FBC) and California Building Code (CBC) as each has specific requirements to meet the climate, fire, and seismic challenges in roof designs. One of the weather events that many of us often overlook is the design for cold and snow climates.
Designing a proper roof for anticipation of snow requires a greater understanding of loads and installation recommendations. As the tile roofing industry, our first reference guide was our Installation Manual For Cold and Snow Regions. We captured the design recommendations of two great snow experts, Leland Gillan and reviewed by Wayne Tobiasson. We added snow retention system products from Terry Anderson to provide design aids that meet the codes while providing long term performance.
This manual was written to assist architects, engineers, owners, and roofing contractors with the process of designing, specifying, and installing tile roofs in areas of snow and ice. Tile roofs have qualities that lend themselves well to use in snow and ice climates. Tile roofs have performed well for centuries in Europe and Asia in high mountain areas.
It is important to learn that it is neither difficult nor expensive to design a roof structurally capable of supporting an accumulation of snow that is much larger than the tile weight. The purpose of most of the designs presented in this manual is to keep the snow on the roof until it melts off. This approach is more compatible with activities on the ground, below the roof, and keeps people off the roof where tiles can be damaged by foot traffic. Many of the topics covered in this reference guide can be used on most roof claddings.
Why is it important to have special call outs in snow regions?
Designing for the snow areas and higher elevations requires the detail of a qualified engineer to provide increased ventilation and retention systems. Intense solar radiation and thin mountain air also promote the buildup of ice dams. Most of the damage reported can be attributed to snow falling and ice damming. The selection of keeping the snow on the roof can provide additional benefits of insulation. The Europeans found the accumulation of snow in fact provides an insulative barrier to the extreme ambient cold and have for centuries designed to keep snow on the roof.
In America, we seem to believe we need to remove the snow through greater roof slopes and materials that allow the snow to slide off the roof. This requires the proper design and understanding for where the snow can safely fall that will not impact other structures, people, or landscaping. We have all seen the pictures of snowbanks that have landed on carports, walkways, or entrances for buildings.
In snow areas the inclusion of increased eave and ridge airflow can significantly reduce potential ice damming. Intense solar radiation will melt the snow on the roof even though the ambient temperature is less than 20°F, causing ice dams on the roof. This is typically found on the eave areas of a roof and often leads to potential safety and product issues. Improper applications may work for years and then fail in a severe snow season.
The development of ice at the eave areas is created as the water under the snow travels downslope and refreezes. Long icicles can form creating safety risks, or potential damage to what is below the eave. As the ice dam moves upslope it can damage underlayment, fastening, flashing, and even roof cladding from the expansion of the ice to the surrounding areas. Icicles may occur in a variety of situations, but extreme examples are usually a sign of poor insulation and ventilation.
For these reasons providing good venting space between the insulation and the roof deck is always recommended to carry off any escaping heat. Our roofing tiles easily provide that option through design options.
Designing the roof to have raised/elevated battens will increase the natural airflow, creating a path for melting snow to travel. Our manufacturers have various batten options that can provide this benefit for easy installation.
Designing the eave to allow greater air entrance. By utilizing one of our raised eave treatments, including a wire mesh, we can increase the air intake at the eave.
Designing the ridge to be raised higher than the adjacent field tile will create a chimney effect helping draw increased airflow through the entire roof reducing ice damming potential.
Snow retention has been used around the world for over a century. Here in the USA, there are numerous product options that can help in snow retention. Snow fences, brackets, clips, and bars are available with proper design recommendations for placement to provide a safe and long-lasting system to hold snow in place.
The upgrade to a better underlayment should also be considered in snowy areas. There are now numerous codes recognizing self-adhering underlayment’s that are approved in snow/cold climate installations. As the design professional, using the option of properly designed snow retention on the roof should be a consideration on your projects.