How Much Water Can Your Roof Shed?

Winter is almost upon us, and that means it’s only a matter of time before the rain and snow start dousing the residents of Colorado Springs. That means it’s time to get out the ladder and clean out your rain gutters, and homeowners everywhere likely groan at the thought. We know that cleaning your rain gutters isn’t a pleasant job, but the truth is that neglecting this important chore can lead to disastrous consequences over the course of the winter. While that rain and snow may not seem like a big deal, the truth is you may not be aware of just how much you’re going to have to deal with. Even in light rain or snowfall, your roof is going to shed a ton of water, and your gutters need to be prepared to handle it.

Rainfall

Rain is pretty common throughout fall and then again into springtime. While a light mist or gentle rain may not seem like it’s that big of a deal, the truth is all that water collecting in your rain gutters can be disastrous if it has nowhere to go. And it’s a lot of water as well. While a little sprinkle may not seem like that much more than a nice water for your lawn, the truth is that your roof is basically a funnel that causes all of that water to accumulate in one place, and boy does it add up quickly when it does.

Let’s put it into perspective. If your roof is 1,500 square feet in size (which is not large by roofing standards), it can shed one thousand gallons of water for every inch of rain that falls. That’s more water than the average American uses in more than two weeks! In particularly heavy rainstorms when an inch of rain falls in roughly an hour or so, it’s easy to see how all that water can quickly turn into a torrential flood when the drainage systems designed to manage it are blocked. That same thing can happen on a smaller scale in your rain gutters!

Snowfall

Snow is a little bit different from rain in that while rain is nothing but water, snow also has an abundance of air packed between the microscopic flakes, which actually means there’s quite a bit less water in snow than there is in rain. In fact, the US Geological Survey estimates that it takes about 10 inches of snowfall to equal the same amount of water as one inch of rain. However, that amount fluctuates based on the snow itself: some flakes are larger than others, some is more densely-packed, and some has a higher concentration of ice rather than pure fresh powder.

The general rule of thumb with snowfall is that one inch of snow falling evenly over one acre of ground equals 2,715 gallons of water according to US Geological Survey numbers. When you consider that an acre is 43,560 square feet, that means one inch of snow on your 1,500 square-foot roof would come out to just 93 gallons of water.

However, there’s something else you have to worry about with snowfall: it rarely stays nice fluffy powder. Snow melts into water, where it can accumulate and re-freeze turning into a dreaded ice dam. Ice dams are extremely dangerous, and can add a ton of weight to your roof, even more than just the weight of the snow.

There’s another issue with snow: the weight. One cubic foot of water weighs 62.4 pounds, and while snow weighs just a small percentage of that, it can add up quickly. If we were to use roughly 12.5 pounds as the average weight of a cubic foot of snow, that would mean a 1,500 square foot roof would suddenly have to bear 18,750 extra pounds… more than nine tons of added weight! Whereas water usually just rolls off your roof and into your rain gutters, snow sticks to your roof, and just 12 inches of snow can add a massive extra burden that may cause extensive damage. And that’s assuming that the snow doesn’t melt into ice, which is much denser and weighs far more.