Managing Snow On Roofs

now is a reality in just about all mountain environments. For those who choose to live in snow country it can be either a blessing or a curse, depending on your perspective and the situation you are currently facing. If you are standing at the top of Schweitzer Mountain Ski Resort the morning after a big snow storm, you will likely be counting your blessings. If you are standing in your driveway trying to move all that snow so you can get to the top of Schweitzer Mountain, you may be saying something else.

Snow and the mountain environment are tough on everything, and your home is no exception. A mountain home should to be able to withstand all that nature throws at it and provide its inhabitants with a warm, dry sanctuary from the elements. When we design homes in the mountains, we pay careful attention to all the details of the building envelope to insure that the finished product will perform well. The most important component in a building's envelope is the roof. A good roof can be the difference between a home that ages gracefully and one that deteriorates quickly and requires frequent maintenance.

It is not uncommon in our area to have several feet of snow on a roof in the winter. Besides being able to support the weight of all that snow, a roof needs to be designed to avoid ice dams, sliding snow, excessive icicle formation, and drainage onto high traffic areas. The easiest and most common sense approach is to keep the roof as simple as possible, avoiding excessive valleys, crickets, dormers, and mechanical roof penetrations. This is easier said than done, and in general the more complex the floor plan is the more complex the roof will be. Simple roofs also may tend to look “plain”. On mountain style homes it is always a fun design challenge to create a roof that looks good, works with the desired floor plan, and handles snow well.

Some general guidelines that we try to adhere to:

• Avoid areas that will trap snow and lead to excessive accumulation, especially on the North side of the roof.
• The roof should be designed with overhangs large enough to provide protection for the walls and windows below.
• Roof slopes lower than 4/12 tend to perform well with metal roofs, which are less prone to leakage and ice dam formation. At these slopes, snow creeps rather than slides and is easy to manage.
• On roof slopes between 4/12 and 6/12, rough textured roofing materials work best. They hold the snow in place and keep it from accumulating and then sliding off in large slabs that can be dangerous. People have been killed by snow avalanches sliding off roofs during big snow winters.
• Slopes greater than 6/12 will tend to shed snow regardless of the texture of the material on them, so roof slopes should be configured to avoid shedding anywhere people might be walking or exiting. The higher the roof pitch, the more often the snow slides off. So in general, the shallower pitch can be more dangerous with bigger slides.
• If the design necessitates a roof slope that drains onto a traffic area, snow retention devices should be provided to hold the snow in place.
• Proper roof ventilation and high R-value roof insulation is essential to minimizing ice dam formation. In some cases, roof snow melt systems or heat tape can be used to combat ice accumulation on eaves and in valleys.
• Shed dormers are easier to waterproof and shed snow better than gable dormers. Shed dormers should be considered if the design and style of the home allow.
• In areas prone to excessive snow accumulation (like Schweitzer and similar alpine environments), gutters should be avoided if possible. Sliding snow tends to tear them off, require frequent replacement or repair. In general, on mountain homes we recommend using gutters only where they are necessary to avoid undesirable drainage situations.
• Try to combine roof penetrations for plumbing and HVAC vents. Routing them to a central chimney helps limit cluttering the roof with vents that sliding snow can damage. Use direct vent mechanical appliances that vent through the wall when possible.

Common sense would suggest that snow accumulation on a roof is a bad thing. In fact, having a reasonable depth layer of snow on a roof is a good thing as long as the roof is designed to handle the weight. It is a sign that the roof is adequately insulated and vented. It also provides an additional level of insulation and protects the roofing material from sun exposure, which is your roof’s worst enemy. A house that has a bare roof when all the others in the area are covered in snow or has excessive ice formation is a sure sign of poor insulation and inadequate venting.

In extreme big snow winters, excessive snow accumulation is unavoidable. Unless your home is purposely designed for much more than the typically required snow load, this is a problem that the best design can’t always resolve. As far as we know, there is only one solution – get out the shovel, call your friends (or winter maintenance company), and get to work!

Selle Valley Construction, a Sandpoint contractor, has some great winter weatherization tips.

If you are looking to build a new home or remodel your existing one, we can help you design a beautiful home that will provide shelter from the mountain weather and provide a sanctuary for your family for generations to come.

Tom Russell, LEED AP, and John Hendricks, AIA Architect

‍Hendricks Architecture specializes in the design of mountain style homes and cabins, often with a rugged, rustic appearance including the use of stone and timbers. Most of the homes we've completed are in mountain resort areas throughout the West. Visit our portfolio for examples of some of our recently completed custom projects.

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