Understanding Your Shed’s Roof Pitch Measurement

I recently added an option to my storage shed plans for increasing the roof pitch from 3/12 to a steeper 4/12 and 5/12 pitch.

Even though I work with this all the time, when I did these calculations I had to stop and think because the reason behind the numbers isn’t intuitively obvious. So I decided this would be a good opportunity to explain what those roof pitch numbers mean.

Roof pitch (or slope) is typically expressed in terms like 3/12, 4/12 and 5/12.

This is a measurement of how much the surface of the roof rises vertically over a horizontal distance.

It’s expressed as a ratio of the vertical rise over the horizontal run, or rise over run, and is always stated in terms of a 12 foot run for standardization..

For example…

For example a roof that increases a height of 3 feet over a 12 foot distance has a pitch of 3/12.
3-12-shed-roof-pitch

A roof that increases 4 feet over a 12 foot distance has a pitch of 4/12.
4/12 shed roof pitch

And a roof that increases 5 feet over a 12 foot span has a pitch of 5/12.
5/12 shed roof pitch

All together

This graphic shows the 3 pitches overlaid together to give you an idea of their relationship to each other. roof pitch comparison

Gable roof example

A gable roof consists of 2 symmetrical slopes together. The run is the measurement to the center of the roof, not the total width.
full-gable-shed-roof-pitch

This shows that the slope is the same even though the run isn’t.

comparison2

  • 8ft wide gable roof shed has a run of 4ft and a rise of 1ft.
  • 10 wide gable roof shed has a run of 5ft and a rise of 1 1/4ft.
  • 12 wide gable roof shed has a run of 6ft and a rise of 1 1/2ft.
  • 24 wide gable roof has a run of 12ft and a rise of 3ft.

My shed plans offer all 3 of these roof pitches. Which one you choose to use will depend on the weather in your area and what you want the final appearance of your shed to be.

The 3/12 pitch roof is the easiest to work on and is the most economical in terms of materials usage. However it might not be suitable in a larger shed if you have a lot of rain or snow load.