Snowflake…snowflake…., how much do you weigh? Right around .002 grams. So, how do a bunch of snowflakes pancake buildings each year? With more snow in the forecast for much of New England, this becomes a very important question.
Generally speaking, it’s not the snowflakes that collapse a building, power lines or a tree. It’s the excessive water content that builds within the crystalline structure of the snow as it morphs from snowflakes, to pellets, to ice. Snow storms that have strong winds also pose a potential problem because they blow snow around, causing snow drifts that can distribute the snow on a roof unequally, which results in a torsional stress on the building’s structure.
Here are some questions to ask yourself:
- Do you know the design of your roof structure?
- Do you have a way to know how much the snow weighs in your area?
- What is your plan to monitor the snowpack on your roofs?
- Do you have personnel trained to safely remove snow from roofs?
- Have you prepared your buildings for winter?
ACTION: To understand designs in different areas of the Northeast, take a look at this Government Data on state snow load information.
Even if you don’t know the exact design of your roof, the information contained in the link above will help you interpolate at what point you should take action. Generally speaking, the states in the southern portions of the Northeast may only have a roof design of 25lbs/square foot (SF) while those in the northern reaches can exceed 80lbs/SF. If you’re concerned, consult with your local structural engineer as they can assist in determining the correct design. Also, partial collapses do occur and these can be just as costly as a total collapse, so consider the value of your inventory, length of business interruption, and time involved to repair the structure.
Snow Water Model Equivalent:
This graph can be used to roughly calculate the water equivalent in your area and thus on your roof. The data shown here is from January 29, 2015, but you can easily adjust the date here. By understanding the snow water equivalent, you will be able to calculate the weight from snow & water on your roof. For example, if the graph (click on graph for a larger view) shows 8” of snow water equivalent, you can easily calculate 8”/12” = .667. Multiply .667 by 62.4lbs (cubic foot of water) and you will be able to estimate that for every square foot of roof you have 43lbs sitting on the roof.
Now that you have estimated 43lbs for every square foot of roof, you can compare that to your design and then take action. If the design of your roof is 40lbs/SF you know immediate action is required to prevent collapse.
Which personnel will you utilize to safely remove the snow & ice? Your own staff? Local help? Contractors?
Is the roof safe to work on or will the moving of snow increase the potential for collapse?
Important questions to ask yourself regarding your own personnel:
- Do they have experience working on roofs, appropriate fall protection, physically able to do heavy manual labor?
- Is Workers compensation (WC) insurance in effect? Are they working in pairs or alone?
- Who will be checking in on them to ensure they are working safely and leave the site at the end of the day?
What are the signs of a building nearing collapse?
- Doors and windows become difficult to open
- Roof leaks develop
- Cracks in wall, creaks occurring, sprinkler head show below ceiling tiles more than usual
- Noticeable sagging in the ceiling
How you can prepare your buildings:
- Some buildings that are open from the floor to the underside of the roof can be “sticked.” That is where a pole is run from the underside of the roof to a supporting structure in the floor.
- Low sloped roofs have a steel roof covering installed.
- Low sloped roofs are identified and employees trained to watch for stress indicators.
- Areas that collect snowdrifts due to building and roof configurations are identified and employees trained to watch areas for quick snow removal.
Do particular buildings or roofs always have large ice dams?
This typically indicates poor insulation in the ceiling or other conditions that allow the building heat to enter the attic space. The ice dams will eventually back water up the roof. The only question is how high does the ice and water shield go up the roof? Once the water backs up beyond the ice and water shield, water will enter the building and cause a water loss. Additionally, poor venting and air escaping into the building will lead to condensation build up on the underside of the roof and rafters, which could lead to issues such as mold.
Certain winters will challenge buildings and people more than others.
The key is to prepare, monitor, evaluate, and take action on a timely basis. With the sites listed here, anyone can monitor the situation and determine when roofs should be cleared. If you have determined the design of the roof structure and that the snow loading is nearing or exceeding the design, the roof should be cleared in a timely manner. Waiting for a forecast of more snow, ice, and rain may be the difference between losing your structure and contents versus having a non-event.
For more information, please contact your Regional Loss Control Director or the Acadia Insurance Virtual Loss Control Team at 1-800-870-1170 ext. 5701.
Additional Resources and Information:
* Source: US Forest Service http://www.fs.fed.us/t-d/snow_load/states.htm
Acadia Insurance is pleased to share this material with its customers. Please note, however, that nothing in this document should be construed as legal advice or the provision of professional consulting services. This material is for general informational purposes only, and while reasonable care has been utilized in compiling this information, no warranty or representation is made as to accuracy or completeness. Distribution of this information does not constitute an assumption by us of your obligations to provide a safe workplace. Maintaining a safe workplace in accordance with all laws is your responsibility. We make no representation or warranty that our activities or recommendations will place you in compliance with law, relieve you of potential liability or ensure your premises or operations are safe. We exercise no control over your premises or operations and have no responsibility or authority to implement loss prevention practices or procedures.