With all of the snow we have had recently, I thought this would be the perfect time to remind you about the importance of checking your buildings for snow loads to help prevent the chance of barn collapses.
What is Snow Load?
Snow load is the downward force on a building’s roof by the weight of accumulated snow and ice. The roof or the entire structure can fail if the snow load exceeds the weight the building was designed to shoulder, or if the building was poorly designed or constructed. Blizzards aren’t the only cause of problems; an imbalance of drifting snow can cause one part of a roof to give, causing a domino effect that affects the rest of the structure.
Warning Signs
Keep a watchful eye on your roof all winter, especially on buildings with considerable loads. Look for the warning signs of overbearing loads, such as:
- Sagging
- Misaligned or Bowed Trusses
- Creaking Sounds
- However, metal buildings, unlike wood buildings, give virtually no warning before collapsing
Calculate
How much snow is too much? Calculating the snow load on your barn takes more than an educated guess. The University of Wisconsin Cooperative Extension Service says that a ballpark estimate of snow load can be made with the following formula:
Calculated Roof Loading (lb/ft2) = Depth (ft) x Density (lb/ft2 /ft depth). The approximate density (lb/ft2 /ft depth) for light snow is 5-20, packed snow 20-40, packed snow with ice 40-58, and ice 58.
For example, a roof with 3 feet of light snow has an estimated roof load of 60 pounds per square foot (3 ft depth X 20 lb/ft2/ft depth density = 60 lb/ft2).
You should know the roof weight limits for your barns and outbuildings, and rebuild or fortify them to withstand worst-case scenario snow loads and meet local building standards.
Safety Tips When Removing Snow
Some failures can be prevented with careful snow removal. The University of Wisconsin Cooperative Extension Service offers the following suggestions:
- Use caution if standing on the roof
- Make sure to wear a safety harness and use securing ladders
- Use a snow rake and avoid chipping or picking away at ice as that may damage the roof
- Remove snow in narrow strips to keep the load somewhat even
- Not all snow needs to be removed. A thin layer of snow can protect the roof from damage while snow is being removed
- Insurance: Check with your farm or ranch insurance agent to confirm what your property insurance covers due to snow load, make sure your policy pays for replacement costs, and to verify that valuable equipment stored in a barn or outbuilding is covered under your farm personal property endorsement
Also know that these conditions could also lead to snow loading problems and increase the chance for roof collapse:
- Adding insulation to the roof without ventilation may cause condensation & eventual rotting of the rafters or deck
- Re-roofing with three or more layers of shingles
- Not correcting observable symptoms of structural problems
For more information on the Do’s and Don’ts of Snow removal or other Winter Weather Safety Tips, contact your local extension educator, myself (kls342@cornell.edu), or check out the Cornell’s Extension Disaster Education Network (EDEN) website. EDEN has a lot of valuable resources for educators, emergency managers, and the community regarding disaster preparedness.
Stay Safe,
-Kayela
Sources:
http://eden.cce.cornell.edu/disasters/Pages/WinterStorms.aspx
https://www.ruralmutual.com/2016/02/10/protect-farm-buildings-snow-loads/
