Posted on January 23, 2020 by Heritage
Snow and ice are typical during winter in many areas of the country. While common, it’s unwise to overlook the devastating effects they can have on building structures. In Part One of this blog series, we reviewed steel building snow loads, how to calculate them and external factors affecting them. In this post, we review building design, snow load minimization and snow load removal considerations that can help keep your structure safe and sound during winter weather.
The best way to avoid damage is to prevent it from occurring in the first place. Considering roof shape, pitch, wind exposure and maintenance requirements during the design process can help eliminate many snow-related issues.
Roof shape and pitch are primary considerations when designing in snow-prone areas as they influence the distribution of snow loads. Snow loads on an open, flat roof, free of obstructions and equipment tend to be uniform. On the other hand, roofs with irregularities and obstructions promote an unbalanced accumulation of snow. Intuitively, higher-pitched roof designs are better able to shed snow than low pitch or flat roofs. However, roof pitches as low as 10 degrees have been observed to shed snow.
Check with your contractor and metal roofing manufacturer to confirm the snow load your roof shape and materials are designed and tested to accommodate. Likewise, gradual shedding (as opposed to immediate) is advisable to prevent damage to people and things the snow may fall onto. (Read the section on sliding snow in part one of this blog series for more details!)
While this may sound counter-intuitive, keeping your roof cold helps prevent ice dams from developing. If a structure’s roof is cold, the snow sitting atop it will stay frozen. This is ideal because if warm air from inside a structure seeps into the attic through unblocked walls, gaps in drywall, and cracks around pipes, fixtures and other ceiling penetrations, it can melt the bottom layer of snow on the roof. This melted snow can run down the roof slope and re-freeze once it hits the cold, unheated edge. This creates an ice dam—a rim of ice that traps water behind it.
Ice dams can can cause roof leaks that damage the building’s roof structure, ceiling, walls, insulation and its interior contents. Additionally, when the ice dam eventually breaks and falls, it will likely take all accumulated snow and even equipment attached to the roof down with it. Not only can that do significant damage to a roof, but anyone or anything in the path of the falling ice dam and snow accumulation is at risk of serious injury.
To keep your roof cold and prevent ice dams, ensure your building has adequate insulation between the interior ceiling and attic. This will help prevent heat from entering the attic and warming the snow on the roof. Also, properly ventilating the attic to allow cold outside air in is one the best ways to keep your roof cold.
Steel roof panels are known for reducing the snow burden on a structure. Steel panels like those Heritage Building Systems offers resist cold weather damage and gradually shed snow and ice. Despite this, however, obstructions like HVAC equipment, firewalls, pipes and vents can promote uneven distribution of snow on any roof. As mentioned above, this can lead to unbalanced snow loads that are a greater threat to any building’s structural integrity. Therefore, be sure to account for these when calculating snow loads.
Because buildings constructed in open areas allow the wind to carry snow away from the building, they are less likely to retain snow on the roof than those in sheltered locations. However, wind also promotes snow drifting, which can cause uneven snow distribution on a roof. If a building in an open area has varying roof elevations, parapets, or other rooftop equipment, snow drifting may cause accumulation at these locations resulting in unbalanced loading conditions.
Even if your structure design supports optimal snow load management and ice dam prevention, once snow accumulates on your roof, your attention should turn to selecting the right removal process. Removal is necessary after every 6” of snowfall to prevent ice dams. However, if ice dams are not of concern, removal after every 12” of accumulation is ideal. Keep in mind that each situation varies and ideal snow removal timing can depend on the building design and roof geometry considerations detailed above. Additionally, external factors like snow density, accumulation, distribution, drifting and sliding are worth considering.
Common snow-removal practices include:
This is generally the best option for regular removal from small, single-story buildings throughout winter by the property owner. For those with taller buildings, roof-raking can still help clear snow from overhangs. As they are the weakest part of a roof, removing excess weight here should be priority. Additionally, keeping overhangs clean can also help prevent ice dams.
When purchasing roof rakes, look for ones with small rollers or bumpers on the bottom of the blade. These help prevent direct contact with the roof surface and protect it from scraping. You should also avoid picking or chipping away at ice as you may damage the roof below in the process. Additionally, it’s a good idea to purchase extra rake extensions. These can help you reach further up your roof, as well as ensure you have replacements ready in case of a mid-season rake break.
This technique a practical option when raking doesn’t quite do the job. Shoveling is ideal for wet, heavy or hard snow that roof raking can’t handle and is best left to professionals. It should also be considered for large, tall roofs, as well as after storms that drop more snow than raking can manage. As it’s not ideal for building owners to shovel their roofs, be sure the professionals performing the service use tools that don’t damage the roof surface. Also, check that they don’t leave footprints of packed snow on your roof; this is a recipe for future ice dam creation.
To keep the snow load relatively even across the roof, experts recommend removing snow in narrow strips. Keep this in mind whether you rake the roof yourself or if you hire a professional to do it.
Regardless of the removal process, it’s ideal to leave at least two inches of snow on the roof. This helps protect it from damage caused by removal methods that can mar steel panels when in direct contact. As with any maintenance activity, there are inherent dangers to be mindful of. To mitigate these risks, ensure anyone servicing your roof uses appropriate safety gear and techniques at all times. Additionally, be aware of surrounding dangers like power lines, which can be deadly if hit with a metal rake.
According to the Metal Building Manufacturer’s Association’s (MBMA’s) Code of Standard Practice, building material manufacturers like Heritage can’t determine which codes apply to your specific project. These must be provided by the building specifier (generally the engineer or architect of record), your local building department or local permit official. Before purchasing a metal building, confirm your codes and loads to ensure you choose materials that can support your structural needs in varying environments.
For more information on how to protect your steel building in winter weather, please check out more Heritage Building Systems resources or reach out to your local representative today!