To some, snow on the roof is a charming winter scene that reminds you of gingerbreview houses at Christmas. It may look nice, until it’s a nightmare.
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Snow on your roof have the right to end up being enough of hazard that it have the right to carry the whole framework crashing down. That’s not a concern restricted to rickety old residences. Any roof deserve to collapse. Even the roof on the Metrodome collapsed, and it was developed specifically through a snowy & cold climate in mind.
It’s necessary to recognize just how a lot scurrently is simply too a lot snow, and also as soon as to get it removed. To know that, you must recognize how much scurrently weighs.
Between my practically 20 years of endure as an ice dam removal skilled, and some research study and number-crunching, I’ve gained some answers (which I’ll acquire to in a minute).
Some components of this post are faster analysis than others. I wanted to share my “lab notes” if you’re interested. In situation not, I’ve likewise tried to make this skimmable.
How much the snow on your roof weighs relies on many kind of determinants. There is no one tough number. Even stating just how a lot any given cubic foot of snow weighs is actually harder than it looks.
Factor: The form of snow.
No two snowflakes are alike. Every snowflake is a tiny, crystalline ice framework. A snowflake drops as soon as a tiny droplet of water falls at a high altitude. As it falls to Earth, extra moisture attaches to the already-frozen droplet, producing little bit branches. By the moment that snowflake reaches your roof, thousands of these branches have actually created, creating a really complicated framework. That structure determines how the snow will certainly fill when it piles up on your roof.
Fortunately, you don’t have to obtain a microscopic lense to evaluate the framework. You can make some generalizations. You either get light, fluffy scurrently, or you gain that thick, heavy, watery snow.
Figure 1. Defined branches (light, fluffy snow).
Figure 2. Less defined branches (hefty, wet snow).
(Images are courtesy of Don Moore of the National Weather Service)
You have the right to additionally predict just how this is going to go, a tiny little, by noting the temperature as soon as the snow starts to autumn. Counterintuitively, cooler weather is much less hazardous to your roof. For example, 10-degree weather tends to develop light, fluffy scurrently. Conversely, 31-degree weather will produce wet, hefty scurrently. The closer it is to freezing (32 degrees), the even more possibly dangerous to your roof the scurrently becomes.
Incidentally, the exact same better temperature varieties are most likely to produce the right problems for ice dams also. Ice dams deserve to form lengthy before you’re likely to face a roof collapse. Because of this, if you recognize you have a residence that is at risk to ice dams, you’ll desire to be on your snow-removal game and also rake your roof after eextremely 6 inches or so of build-up.
Key points:No two snowflakes are achoose, which renders it hard to make generalizations around scurrently weight.Snowflakes through well-identified branches are lighter, fluffier, and less dangerous.Colder weather produces lighter snow. The closer temperatures are to freezing, the wetter, heavier, and also even more dangerous scurrently becomes.The very same temperature problems that produce heavy snow also create the right weather conditions for ice dams.If your house is prone to ice dams, rake your roof after eextremely six inches of snow accumulation.
Factors: Weight and also water content.
Of course, none of this discussion on snowflake form and scurrently form tells us a lot about the actual weight of snow. For that, we have to dig in and also crunch some numbers.
First, let’s create a couple of facts and also obtain our bearings right.
First, scurrently is simply frozen water, so measuring the weight of one cubic foot of water is a great start, also though scurrently holds various amounts of water, relying on its form. One cubic foot of water weighs roughly 62.4 pounds. That’s the size of a box measuring one foot, by one foot, by one foot
But one cubic foot of snow will weigh less than that, and also the amount it weighs will certainly depend on just how much water is actually consisted of in the snow. The actual water content of scurrently generally varieties from 5% to 32%. 20% is about average for a Midwestern snowautumn. This suggests the snow weighs 20% of what pure water would weigh. That means the exact same volume of snow just weighs 12.48 pounds per cubic foot. If the saturation reaches 32%, by the method, you’re looking at 19.92 pounds per cubic foot.
Most of us don’t measure snow in terms of feet, so let’s break this down right into inches. If you divide 12.48 (what one cubic foot of average scurrently weighs) by 12, that amounts to 1.04. That implies 1’’ of average snow accumulation weighs 1.04 pounds per square foot.
All that math brings me to a rule of thumb I’ve used for years. It’s one that simplifies matters, because there’s really no straightforward way to meacertain the water content of the scurrently on your roof – not without going through a bunch of crazy, maybe dangerous, time-consuming shenanigans nobody in their right mind wants to go via. I’ve watched scurrently geeks talk about cutting a cubic foot of snow off the roof, taking it inside to melt it down, and measuring the results. That’s madness. For one thing, it implies gaining up on your wet, icy, slick, slippery roof in the dead of winter, attempting to reduced an accurate cubic foot of scurrently and attempting to haul it all down to conduct what amounts to a usemuch less, time-devouring experiment.
So here’s my educated, math-increated rule of thumb:
1 inch of snowfall on the roof weighs about one pound per square foot.
We’ve already establiburned the water content of snow have the right to selection anywhere from 5% to 32%, which would certainly suppose 1” of scurrently ranges from .26 pounds per square foot (“PSF”) to 1.66 PSF. To uncover the average weight of the scurrently, include those numbers and divide by 2. We acquire an average of .96 lbs., which is mighty cshed to 1 pound. (However, you might note best amethod that especially wet or heavy snow can easily be closer to 2 pounds PSF—note the problems outside, and also use your prevalent sense).
From that, you’ve gained a handy formula you can usage to recognize about just how many type of pounds of snow are on your roof: simply multiply the inches of scurrently that have fallen by the square footage of your roof. That number is around the variety of pounds of scurrently on your roof.
So, for example, if you gained 3 inches of snowfall and also you have an average-sized 2000-square-foot roof, your roof is holding 6000 pounds of scurrently. That’s like melting two stripped-dvery own SUVs (each weighing 3470 pounds) into a slab of steel and also laying that slab on your roof.
That number have the right to be even more dramatic, relying on a few determinants.
If the scurrently on your roof is incredibly wet and also hefty, you can multiply the “inches of scurrently times square footage of roof” sum by 1.66 to get a worst-case scenario figure. (In the above instance, that comes out to 9960 pounds.)
For an average-size roof (around 2000 square feet) spanned in hefty wet snow, a good ascendancy of thumb is the weight of one compact SUV (3,470 lbs.) on your roof for every 1-inch of scurrently.
It is likewise vital to remember that that math doesn’t take right into account any type of ice you have on your roof, which weighs a lot even more than heavy wet snow weighs.
Key points:The water content of any provided cubic foot of scurrently deserve to strongly influence how much the scurrently actually weighs.1 cubic foot of water weighs 62.4 lbs. One cubic foot of scurrently normally weighs 5% to 32% of that. In the Midwest, the water content of a cubic foot of snow avereras about 20%, or 12.48 pounds. By the way, namong our scenarios takes into account the weight of scurrently after it has soaked up falling rain. Rain deserve to quickly double the weight of currently heavy/wet snow.1 cubic foot of ice weighs 57.2 lbs, which is even more than 5 times the weight of also the wettest, heaviest snow. Namong our scenarios takes right into account the visibility and/or weight of ice , which is almost constantly accompanies snowThe average roof in the U.S. measures around 2000 square feet.The average compact SUV weighs about 3470 lbs.A dominion of thumb – concerning the weight of average snow: One inch of scurrently, on average, weighs 1 lb. per square foot. That understanding is what tells you that mere 1.75 inches of average-weight scurrently on a typical roof is the identical of one compact SUV parked on the roof.A dominion of thumb about the weight of light, fluffy snow: One inch of scurrently weighs 0.26 pounds per square foot. That indicates for eexceptionally 6.5 inches of snowfall you’ve obtained the weight of a compact SUV on your roof.A dominion of thumb regarding the weight of hefty, wet snow: One inch of scurrently weighs 1.66 pounds per square foot. That means that for eincredibly single inch of heavy, wet snow on an average-sized roof, you’ve got the identical of one compact SUV parked up tbelow.
How much weight have the right to the average roof support? How a lot snow deserve to it take?
Determining your roof’s capacity to take care of snow is even even more complex, bereason weight is not the just aspect affecting just how a lot your roof have the right to take care of.
For instance, what condition is your roof in? An older roof via rotted supports (you may not recognize about yet) deserve to take a lot less snow than a new, totally functional, well-maintained roof.
The pitch of the roof provides a large difference, as well. A steep roof does a better task of dealing with snow than a level roof does. The roof-pitch affects weight distribution, permitting it to host a small even more snowfill safely. In addition, the slope of the roof helps to dump some of that scurrently back on the ground, rerelocating even more anxiety. The wind also blows the scurrently even more easily off of a steeper-pitched roof.
A level roof, by comparison, is in risk of collapsing a lot quicker. Most roof collapses happen on flat roofs because all of that weight simply sits tbelow (i.e. dead weight via no disbursement or displacement whatsoever). When you acquire simply a couple of inches of scurrently on a level roof, it quickly becomes the tantamount of parking a automobile or 2 up tbelow. Not great.
The year your house was constructed also matters. If your home was built after 1971 (in Minnesota for instance) it would have been held to long-standing structure codes that require roofing to assistance 40 pounds per square foot. If your home was developed in the 1920s, but, your roofing deserve to probably withstand also just 30 pounds per square foot.
Even all those roofing determinants are not the only determinants that recognize the likelihood of a collapse. The weather matters, too.
Wind is a variable. Snow doesn’t loss in a nice, neat, even carpet to start via. Snow drifts. More wind suggests more drifts. You can have actually had actually 8 inches of scurrently last night, yet that doesn’t suppose there are 8 inches of scurrently spreview evenly over your roof, like frosting on a cake. Some parts of your roof won’t have much snow at all, and also some parts might have a 2 foot or even a four-foot drift. That’s putting many push on one focused area of your roof. Aobtain, not great.
Winter rain is a trouble. The snow on your roof absorbs rain favor a dry sponge, and as an outcome becomes much heavier. And if we have actually snow melting during the day and also re-freezing at night (aget, the perfect conditions for an ice dam), you could be structure up a layer of ice atop your roof. The presence of “Ice” completely alters the game as soon as it concerns the question “How a lot does scurrently weigh?” With the existence of ice, the pack on your roof might quickly exceed that moisture level of 32%, which indicates you might be handling 2 or also three pounds per square foot (per inch of snow). That’s the equivalent of a Toyota Prius with an illegal variety of passengers, two bikes on the roof, and a number of clowns in the trunk.
If every one of this is making you scratch your head as you attempt to account for every single factor on the list, you can constantly use the figures gave by the Institute for Business and also Home Safety (IBHS), which offers stormy numbers based on the type of snow. Note that they neglect the remainder of the determinants, which have the right to affect whether a roof collapses, but their guidelines reprimary useful nonetheless:
Fresh snow: 10-12 inches of brand-new snow is equal to around one inch of water, or around 5 pounds per square foot of roof room, so you might have actually approximately 4 ft. of brand-new snow before the roof will certainly end up being stressed.
Packed snow: 3-5 inches of old scurrently is equal to one inch of water, or about 5 lbs. per square foot of roof room, so anything even more than 2 feet of scurrently might be as well a lot for your roof to take care of.
Total collected weight: Two feet of old scurrently and also 2 feet of brand-new scurrently might weigh as a lot as 60 lbs. per square foot of roof space, which is beyond the typical snow fill capacity of a lot of roofs.
Ice: One inch of ice equals one foot of fresh snow.
If you want to simplify all of this also even more, and also play it really safe, you have the right to take my advice – as a guy that has actually faced scurrently and ice on rooftops for almost 20 years:
Remove the scurrently at 2 feet if you have actually a more recent, pitched roof that is in decent shape, and also if the weather has actually not made it heavier than normal. Check for bigger drifts. Due to the fact that the majority of of these contributing components rise the weight and also danger of the snow you can’t really go wrong by playing it safe. In enhancement, 2 feet is likewise around the the majority of your average roof rake is going to be able to handle; wait a lot much longer than that and you might well have to speak to in a professional roof snow removal organization, particularly if that scurrently happens to ice over and also harden while you put off having to rerelocate it.
Obviously, if you have actually an older roof, live in a made home, have actually a company with a level roof, or have a flat porch roof on your house, then you’ll want to be even more conservative. In those situations, I recommend utilizing 12 inches of scurrently as your line in the sand also for snow removal.
What if you shed track of just how much snow is up tbelow, or you don’t have actually a great vantage point to guesstimate from the ground? (After all, you’re busy. You’re not watching eincredibly weather report and also you probably won’t go up there via a ladder and ruler.)
If that happens, go about your residence opening the doors and the home windows. If any of them provides you trouble, that can intend that the snow has actually compressed your roof, in turn placing press on the door and window frames. If that’s taken place, you have far too a lot snow for your roof to bear and you must obtain the scurrently rerelocated STAT.
Key points:Older roofs or roofs in poor form may not be able to withstand also as a lot snow as some published guidelines can suggest.Flat roofs commonly hold the leastern amount of weight, depending upon their construction.Excessive rainfall or a constant thaw-and-freeze cycle deserve to quickly boost the weight of the roof snow to dangerous levels. Get more conservative about scurrently removal if you watch these problems.Your finest bet is to treat 2 feet of snow as the maximum snow load a healthy, modern, sloped roof have the right to take, and also to be vigilant around watching for scurrently drifts that could be deeper and also more dangerous.If you have an older roof, live in a produced residence, or have actually a home via a flat roof, then it pays to be also more conservative: use 12 inches as your tough limit for scurrently removal.If you find it tough to open up any type of of your doors or windows this is a authorize the snow fill has actually grvery own too hefty for your house to bear. Seek the assist of an ice and snow removal company immediately. You might even consider spending a night or 2 in a motel. Roof collapses are exceptionally real, and they have the right to often times lead to tragedy. Give them the serious attention they deserve.
What is the best way to remove scurrently from the roof?
Always stand also on the ground. Never work from a ladder. Use a roof rake through rollers or a plastic edge to pull the scurrently off of your roof. Make certain you use an extendable pole so you’re able to stand much sufficient away from the edge of your roof that you’re not standing straight in the line of fire as the scurrently comes crashing down from your roof. The last thing you want to carry out is component your hair via a block of ice
Never, ever before acquire up on your roof. Professionals will obtain up tbelow through shovels and steamers, but you’re paying us to do that, and also we’re trained & insured against mishaps. You don’t need or want to risk injury, fatality, or discapability by standing on a slick ladder or a slippery roof in the dead of winter.
If you don’t feel confident that you have the right to acquire the project done without hurting yourself, get a professional. Don’t injure yourself just to conserve a few bucks.
Want to learn even more about the weight of snow?
No trouble. I’ve got some sources for you.
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Remember, a roof collapse can cause significant injury (or worse) to you or your loved ones, to say nopoint of the thousands upon thousands of dollars in repair expenses, raised homeowner’s insurance premiums, and also various other major hassles. At the finish of the day, it’s necessary not to acquire also hung up on waiting till you’ve gained the absolute maximum amount of scurrently up there. If you think you can have to rerelocate that scurrently, it’s more than likely a great idea to do so.