In residential solar, knowing the roof pitch is an essential part of preparing for any solar design and installation. The roof pitch can affect a system’s energy production. Sometimes, steep roofs include a cost adder because it is more difficult to install. A roof’s pitch or slope can be referred to both as a degree angle and a ratio of vertical rise over horizontal run.

Knowing how to go from a rise over run ratio to degrees is a helpful skill. In this short video, HeatSpring instructor Sean White shares a quick trick to turn the rise over run ratio into a degree angle.

Okay, roof slope angle shortcut. Here’s what we’re going to do for a roof slope. And so we have a 4 and 12 roof. They talk about rise and run with a roof.

And so a 4 and 12 roof means that there’s 12 units distance (that would be the run). And then there’s four units rise. 

A lot of people talk about inches, but it could be feet and it could be centimeters, because it’s just a ratio. 

So we go 4 divided by 12 and that gives us 0.333. Then we take the inverse tangent of 0.333 and that gives us an 18 degree roof slope. 

That’s all there is to it. If you have roofer buddies, you can show them this trick. You could figure out the slope of a roof in less than 5 seconds with this trick. It’s an 18 degree slope, and it’s not that hard to remember.

And it impresses people because it uses trig[onometry]. 
For more great solar tips from Sean, enroll in his 40-Hour NABCEP Advanced PV Certification Training and CEUs course.