Snow weight on a roof – How to minimize risks and protect your home?

Knowing when and how to remove snow from your roof can be tricky, as several factors influence snow accumulation and weight. An excessive load can put your home's structure at risk, but clearing snow too early or too often can also cause unnecessary damage.

What are the signs that it’s time to clear your roof? How can you assess the weight of the snow? What precautions should you take to avoid damaging the roof?

In this detailed article, learn everything you need to know to safely and effectively remove snow from your roof at the right time.

How to calculate the total load of snow on your roof?

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How much does the snow on your roof weigh? - Load calculation formula

Calculating the snow load involves considering not only the thickness of the snow but also its density on your roof.

For a quick basic calculation, you can use the following formula:

P = (S x 1.25 lbs) + (I x 5.2 lbs)

Where:

• S: Snow thickness in inches

• I: Ice thickness in inches

The result P represents the total weight in pounds per square foot.

Keep in mind that rainfall affects the weight of the snow on your roof. Snow absorbs precipitation, increasing its density and overall weight. If you want a more precise calculation, you can use the OMNI calculator.

This tool factors in the length, width, and slope of your roof. Depending on the snow thickness and type, the calculator adjusts the estimated snow weight accordingly.

Types of precipitation and snow weight

The Insurance Institute for Business & Home Safety (IIBHS) has outlined general guidelines for assessing the snow load a roof can support.

1) Fresh snow

10 to 12 inches of fresh snow is roughly equivalent to 1 inch of water, weighing about 5 pounds per square foot of roof. This means a roof can typically support up to 4 feet of fresh snow before becoming at risk.

2) Compacted snow

3 to 5 inches of compacted snow is equivalent to 1 inch of water, also weighing about 5 pounds per square foot. In this case, a roof can handle up to 12 inches of compacted snow before experiencing structural stress.

3) Ice

Ice is significantly heavier than snow—1 inch of ice weighs as much as 12 inches of fresh snow. This makes it especially important to monitor ice buildup closely.

In Quebec, winter temperatures fluctuate greatly, causing multiple layers of snow to accumulate on your roof. Weather conditions like rain, freezing rain, and sudden thaws can create alternating layers of ice and compacted snow.

This can lead to water infiltration and severe damage to your home. To prevent issues, regularly inspect your roof throughout the winter.

Thinking about renovating during the colder months but feeling unsure? Check out our article: 5 good reasons to renovate in winter.

How much weight of snow can a roof hold (in pounds per square foot)?

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Up to a certain point, snow can be beneficial. In fact, it adds insulation to your roof and, in a way, protects your home from the elements.

Any load exceeding 20 pounds per square foot is considered dangerous. According to the Insurance Institute for Business & Home Safety, if your home is not damaged or deteriorating, it should be able to withstand this load without structural issues. However, certain factors need to be considered for a more complete answer, as the roof style and the quality of the snow will impact this.

Depending on the residence, roofs can come in many shapes and designs. In Quebec, for example, you’ll find:

• Gable roofs (pitched roof)

• Lean-to roofs (shed roof)

• Valley and eaves roofs

• Multi-pitched roofs (2 or 4 sides)

• Basin roofs

• Flat roofs

The type of roofing is often determined by a local engineer based on your home's location and various other factors. Depending on the environment, materials and the roof structure will vary to support the different types of snow typical for the region.

If the structure of your home has changed over the years, your roof may be more fragile and susceptible to the elements.

How to know if there's too much snow on your roof?

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Ice buildup on a roof is very dangerous. It weighs five times more than snow and can also lead to significant issues inside your roof. During winter, snow only melts under two specific conditions: when exposed to sunlight or if heat escapes from your home.

There are clear signs of excessive snow load on your roof. If your interior doors no longer close as easily as before, if they drag on the floor, or if you notice cracks in your walls, it’s time to take action. Unusual and repeated creaking sounds can also indicate an excessive snow buildup.

Similarly, if your ceiling starts to deform, immediate action is necessary. If you notice too many of these signs, it’s recommended to evacuate your home and take prompt steps to remove the accumulated snow.

As a homeowner, you are responsible for the safety of your home, not only for yourself and your family but also for anyone who may approach your property. Paying attention to warning signs and preventing snow accumulation will help you avoid disastrous consequences related to snow collapse, or worse: the collapse of your roof.

If in doubt, contact professionals in your municipality to determine the maximum snow load your roof can handle.

Elements to consider before clearing snow from your roof

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As you’ve likely understood, there are many factors to consider before deciding to remove the snow from your roof. The first and most obvious factor is the amount of snow on your roof.

Next, the roofing material and the slope of your roof will influence how easily the snow can be removed. For example, a metal roof allows for better snow removal, unlike a shingle roof. The same goes for the slope angle: if it’s shallow (less than 3/12), melted snow won’t be able to drain easily and will form icicles. If your house is old, the weight it can support may differ. Precipitation and temperature fluctuations also affect the snow's quality and density.

To protect your home, snow removal should be done by experts. This way, you can avoid many potential problems.

It’s important to be aware of the dangers of roof snow removal. If done incorrectly, the consequences can be severe. It’s not uncommon for permanent damage to occur to the roof and materials. There's also the risk of falling or slipping from the roof. Never attempt it alone, and always gather information first. When snow falls from your roof, it’s like an avalanche, which can be fatal.

Be mindful of where the snow will land and keep pedestrians away from that area. Don’t try to remove all the snow from your roof; the layer of ice attached to the roof actually serves as protection. You may end up causing damage rather than being helpful.

FAQ

Can snow be too heavy for a roof?

Yes, if the snow exceeds the weight capacity your roof can handle, it can cause structural damage. Typically, any snow load over 20 pounds per square foot is considered dangerous.

On average, how much weight does snow add to a roof?

The weight of snow on a roof varies depending on its type. Fresh snow weighs about 5 pounds per square foot for every 10 to 12 inches. Compacted snow weighs around 5 pounds per square foot for every 3 to 5 inches. Ice, however, is much heavier, with 1 inch of ice equaling the weight of 12 inches of fresh snow.