About Roof Pitch

“Roof collapses under weight of snow and ice,” says New York Times. Even here in the Southwest, we’ve heard the news headlines coming from the rest of the country as winter storm after winter storm pounds the eastern seaboard. So why did so many of those roofs cave in? A major contributing factor was the roof pitch.

So what is roof pitch? Roof pitch is the vertical rise of your roof divided by the horizontal span (or run). It is typically expressed with the rise first and run second, with the run denominated by the number 12, giving a ratio of how many inches of incline there is to each foot of run. For example, 3:12, 4:12, 5:12, and so on.

Are you asleep yet?

Don’t worry, here it is in simple terms. Roof pitch is the slant or steepness of your roof. You might have a very steep slant with high peaks or no slant at all (flat). The term flat roof is misleading however, since even a flat roof is not truly flat. It should have a 1 to 2% minimum slope so that water runs off.

And that is the primary purpose of pitching a roof — to redirect water and snow so it won’t pond on your roof and cause serious damage to your roofing materials or even catastrophic collapse. Typically, areas with higher rain or snowfall have a steeper pitch — some of the roofs on eastern seaboard just didn’t have enough pitch to withstand the heavy snowfall, or worse yet, they were built correctly but the roofs weren’t well maintained.

Here in the Southwest, particularly the desert areas, we can get away with nearly flat roofs, both on commercial and residential properties, thanks to our dry climate. However, the mountainous areas of the Southwest get plenty of snow, so a “flat” roof requires a great deal of roofing expertise, and in some cases it may not be the best option.

Every state and community has regulations and requirements for the pitch of a roof. It is a good idea to check with a professional roofer or building official to learn what those regulations are before picking out a building or home design that might not work in your area.