Q: My roof is old and I am worried about the snow load on my roof. How much does snow weigh and how do I know if my roof can handle the weight?
A: Some of the smallest snowflakes are no larger than the diameter of a human hair. It’s hard to believe that something so small can weigh so much!
However, it’s true—snow is heavy and snow load on your roof can absolutely cause damage. Here’s what you need to know.
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How Much Does Snow Weigh?
The weight of snow depends on the type of snow in question. To calculate the weight of snow, you take 7.48 gallons of per cubic foot of water, which is about 62.4 pounds. You then divide it by the amount of snow (in inches).
But here’s where it gets interesting: not all snow is created equal. The weight of snow can vary dramatically depending on how much water is in it—what meteorologists call the “snow to water ratio.”
Light and fluffy snow has a high snow-to-water ratio, typically around 15 to 1 (meaning 15 inches of snow equals 1 inch of water). Sometimes, especially with very cold storms, it can be as much as 30 to 1! In these cases, 12” of light and fluffy snow, will weigh about 5.2 pounds.
Heavy, wet snow is on the opposite end of the spectrum, with a ratio as low as 5 to 1 (5 inches of snow equals 1 inch of water). That means it’s far denser—and heavier. For example, just 5” of wet snow can weigh about 12.5 pounds.
So, whether you’re dealing with powdery snowflakes or the heavy, slushy stuff, the snow load on your roof can add up quickly. Knowing which type of snow has landed can give you a better idea of how much weight your roof is really supporting.
With this information, you’re now likely wondering about the weight of snow load on your roof. There is a calculation for this, too!
Is Recent Snowfall a Cause for Concern?
If you’ve been eyeing the drifts outside with a mix of suspicion and dread, here’s a bit of good news: the recent snowfall has mostly been the light, fluffy kind. This type of snow, while impressive in appearance, tends to be much lighter and less taxing on your roof than dense, wet snow. In other words, unless we get a sudden spell of heavy, wet snow, your roof is under less stress than it might seem.
But what does this mean in practical terms? Those picturesque piles may look daunting, but compared to the concrete-like weight of wet snow, they’re much less likely to threaten your roof’s structural integrity. Still, it’s wise to keep an eye on future forecasts—conditions can shift quickly!
Putting It Into Perspective: Snow vs. Pickup Trucks
To give you an idea of just how much weight your roof might be carrying, let’s use something we can all picture—a pickup truck.
- Light, fluffy snow: If your roof accumulates one foot of the powdery stuff, that’s roughly equivalent to parking a single pickup truck on top of your house. Not something you see every day!
- Heavy, wet snow: Now, imagine that same foot of wet, dense snow. Suddenly, you’re nearly tripling the load—think three pickup trucks, all lined up on the roof.
Stacking up more snow only multiplies the problem:
- Two feet of light snow? Picture two pickup trucks overhead.
- Two feet of wet snow? It’s essentially the weight of about six pickup trucks pressing down.
This comparison really highlights why it’s so important to keep an eye on snow accumulation as winter goes on. Even if the snow looks innocent, your roof could be holding a fleet of Fords without you even realizing it!
Calculating Snow Load on Roof
Calculating snow load on your roof depends on two factors: whether it’s a flat roof or a pitched roof. The snow load will be different depending on the construction of your roof.
Measuring Snow Load for Flat Roofs
Even though we typically measure snowfall in inches or feet, you’ll want to think of it in terms of feet. The easiest way to measure snowfall on a flat roof is to take a yardstick and measure what looks like the average overall snowfall. If there is 18 inches of snow this is expressed as 1.5 feet.
You’ll then take the depth of snow in feet and multiply it by the weight of 1 cubic foot of snow. This is 6 to 8 pounds for fluffy snow and 20 pounds for wet snow. The same volume of ice can weigh 3 times the amount.
To put things into perspective, let’s say you double the snowfall to 2 feet. For fluffy snow, that’s about the weight of two pickup trucks spread across your roof. For wet, heavy snow, it can be as much as six pickup trucks sitting on top of your house. That’s a lot of weight for any roof to handle!
After you arrive at your answer, multiply it by the square footage of your home. This is how much snow load or pounds of pressure from snow is on your roof.
Measuring Snow Load for Pitched Roof
With a pitched roof, you’ll need to know how much snowfall is expected and determine the pitch of your roof. You’ll need to measure the rise and the run and divide the answer by the run, then convert it to a fraction ratio of 12.
From here, it’s best to use a snow load calculator such as this one from Cornell University.
With the weight of snow fresh in your mind, here’s how you can tell if your roof can handle the weight.
Source: https://courses.cit.cornell.edu/arch264/calculators/example2.3/index.html
Recent Roof Collapses from Heavy Snowfall
If you’ve been watching the news or chatting with neighbors, you’ve probably noticed a troubling trend: several buildings have recently suffered roof collapses due to the sheer weight of accumulated snow. In fact, throughout the past few weeks, multiple incidents have occurred across the region, with local authorities reporting a spike in collapses—sometimes within just days of each other—following particularly intense storms.
Heavy, wet snow plays a big role in these incidents, as it can rapidly pile up on rooftops and quickly exceed safe load limits. Commercial buildings and older homes tend to be especially vulnerable, particularly if maintenance has been deferred or if snow is not removed promptly after major weather events. These collapses serve as a reminder of just how important it is to calculate your roof’s snow load—and to take timely action to clear excess accumulation when necessary.
Can my Roof Handle Heavy Snow?
Even if math isn’t your strong point, we can give you a general idea if your roof can handle a snowstorm or otherwise significant snowfall.
Image source: Insurance Institute for Business and Home Safety
According to the Insurance Institute for Business and Home Safety, most residential roofs are able to withstand a reasonably heavy snow load before becoming stressed. Once the snow load accumulates to 20-25 pounds per square foot, this becomes the danger zone.
Generally, this means that most roofs can safely support up to 2 feet of light, fluffy snow—especially snow with a water-to-snow ratio of 10 to 1—before any cause for concern. However, as snow becomes wetter and heavier, or if additional accumulation occurs without melting, the risk to your roof increases significantly.
When your roof becomes stressed due to the weight of snow, you might begin to notice:
- Noticeable bends or cracks in the attic.
- Damaged or splintering rafter beams.
- New cracks in drywall or plaster around door frames.
- Doors are suddenly sticking when they used to open with ease.
- Cracks and leaks in the ceiling.
- Sections of your roof are sagging.
The good news is that roof collapse typically doesn’t happen all at once. It’s a process of breaking down until your roof can no longer handle the weight.
However, if you suspect that your roof cannot handle significant snowfall, it’s important that you contact a roofing contractor in MA. A roofing contractor can help evaluate whether your roof is subject to collapse due to snowfall.
Book Your Roof Replacement Before the Spring Rush
If you are worried about the structure of your roof, it’s better to call Coastal Windows & Exteriors sooner than later. Spring appointments are already booking up and there’s still time to get ahead of the rush and take advantage of our winter promotion! Contact svanderbilt@mycoastalwindows.com to get started.
