Snow & Roof Overload
Snowstorms can impact residents in numerous ways. While focusing on driving safely under adverse road conditions, school closings, and other challenges, we often forget about how damaging excessive snow loads can be to our home and farm structures. News of roof collapses periodically draw attention to this serious issue.
All snow is not created equal. Snow can have a wide range of moisture contents, and this moisture content directly controls the weight the snow.
‘Dry’ snow, that light fluffy powdery stuff, is much lighter than the dense and heavy ‘wet’ snow. For example, two feet of a typical ‘dry’ snow will exert a load of just under 10 lb/ft2 on a flat surface, while the same depth of a ‘wet’ snow can exert over 40 lb/ft2.
In West Virginia, snow can be on either end of the spectrum. On the ‘wet’ end of the spectrum, under a three-foot snowfall, the maximum estimated ground snow loads approached 70 lb/ft2. Even so, the actual snow load on a roof is often less than the load on the ground. This is because winter winds can blow some of the snow off of the building; however, if snow drifts occur on the roof, loads can significantly increase. Typically, as roof slope increases, the snow load decreases because snow tends to slide off instead of build up.
There are a number of reasons why roofs can fail. If the actual snow load on the roof is greater than the design load, then there is a danger of collapse. Improper building design and faulty construction can also result in failure, as can older buildings that have been subjected to decay or damage. In addition, buildings are typically only designed to hold the design loads for about a month before structural fatigue weakens the roof and collapse can occur.
Many people subscribe to the opinion that snow should never
be allowed to accumulate on a roof and should be removed quickly. However, the problem with this approach is
the risk of injury and/or roof damage. Therefore, the safest option is to
remove snow only when absolutely necessary. Unless you are a professional
roofer with the proper safety equipment, do not go on your roof and simply
shovel off the snow. The risk of falling or damaging your shingles is far
The best do-it-yourself method is to use a snow rake – a long, adjustable-length pole with a flat piece attached to the end at a 90-degree angle. A snow rake will remove snow from the eaves and as far up the roof as you can reach with the rake. Staying away from overhead service entrances (powerlines) is extremely important since the rake could conduct electricity. Snow rakes are available at any hardware or home improvement store.
If using a snow rake is not feasible, then pre-planning is necessary. Start scouting reputable companies in the fall to enlist their aid so you’re not scrambling to hire one at the last minute. They also may be able to assist you with installing roof anchors for future fall protection when accessing your roof year-round.
Wood buildings often exhibit certain signs before they fail. Sounds such as creaking, cracking and moaning of building components can indicate potential failure. Any bowing of structural members should also be viewed as a warning sign. If you notice any of these signs, safely and quickly evacuate the building.
Every fall, and before big storms, it is also a good idea make sure all gutters and downspouts can flow freely to help prevent ice buildup and properly drain melting snow off of roofs.