When Should I Remove Snow from My Roof?

by Scott Bohne, AIA, NCARB, CCS, CCCA, LEED AP

DATE PUBLISHED: APR 1, 2021

Occasionally, we are asked “When is the right time to remove snow from my roof?” Unfortunately, this is a difficult question to answer. It depends on the amount of snow and the amount of snow drifting your roof is experiencing. It also depends greatly on the water content of the snow. New snow may be very dry, light, and fluffy. Old snow may begin to break down and consolidate. Think of the snow like a sponge. If the weather warms and we get rain, the snow absorbs that water.

How much does snow weigh?

The weight of snow may vary between 5 and 20 pounds per cubic foot depending on the density and water content. You must also consider the depth of the snow drift that may occur on your roof. Winds may deposit large quantities of snow around changes in roof elevation. The total weight being applied to your roof is not only determined by the amount of snow that falls, but also the snow that drifts on the roof.

Another factor may be whether your roof has been holding or shedding the accumulated snow. Snow accumulation on a metal roof with good slope may be minimal. An asphalt shingle roof with minimal slope, or a low slope roof, may hold all the snow that falls and drifts on it. Ice is very heavy. An ice dam forming at your roof eave weighs 57 pounds per cubic foot, (4.75 pounds per inch of thickness). The water forming behind the ice dam may weigh 5.2 pounds per inch of thickness. Ice dams may not only exceed the load capacity of your roof, they may also lead to rotted plywood. Those pretty icicles are an indicator that your roof has an ice damming problem.

So now that you know the facts, what’s next?

Commercial Building Owners

Understand what loads your structure can handle and understand the weight of snow so that you can monitor accumulation and drift areas so snow can be removed at the appropriate time. A structural engineer can analyze your roof and provide you with valuable information regarding snow and snow drift capacity.
Listen to your structure. If you hear creaking and groaning, you’re on borrowed time.
Monitor the roof for snow loading. Weigh the snow by removing a set amount and weighing it.
We recommend using 5-gallon buckets to invert, load, remove, and weigh.
Make sure your roof drains are clear of ice and debris. A clogged roof drain restricts the water from getting off the roof.
If you have concerns or doubts, hire a roofing company that is licensed, bonded, and insured to remove the snow from your roof.

Residential Homeowners

Listen to your structure. If you hear creaking and groaning, you’re on borrowed time. Monitor your interior doors and gypsum board. If the doors start to stick or you see cracks in the gypsum board at the door openings, your structure may be overloaded.
Monitor the roof for snow loading. Weigh the snow by removing a set amount and weighing it. We recommend using 5-gallon buckets to invert, load, remove, and weigh.
Be sure that your gutters, downspouts, and drains are open and draining properly. If they are frozen shut, call a specialist to utilize methods such as steaming to open the drains, gutters, and downspouts.
Never shovel the roof completely clear. This may damage the roofing and the roof flashings. Leave 6 inches of snow for your footing, and to protect the roofing.
Install heat tape where appropriate to reduce ice dams or cut channels in the dams to relieve the water that may back up behind the dam.
If you have concerns or doubts, hire a roofing company that is licensed and bonded to remove the snow from your roof.

Scott Bohne, a Principal in the Anchorage office, brings 40 years of architectural experience. He has taught roofing on the university level and heads RIM’s Specifications Department and Exterior Thermal Envelope Studio, which emphasizes roofing repairs and replacements.