You can also divide the rise over run multiply by 100 and get a percentage.
Pole barn lean to roof pitch.
Lean to shed roofs develop an interesting problem as they get larger.
A 4 12 pitch is around 18 5 degrees but not exactly.
Roof pitch refers to the amount of rise a roof has compared to the horizontal measurement of the roof called the run.
The run for a lean to shed rafter ending into a wall should account for the ridge board nailed into the wall where the tops of the rafters rest into.
If the roof pitch is very steep at all then it will rise to a height that becomes unsightly.
This ugly design is most often avoided by installing a low slope roof to keep the rise of the roof at a minimum.
A change in roof pitch between the existing building and the lean to or the lean to high side being lower than the existing structure can result in snow drifting and snow slide off loads which need to be carefully considered.
In other words if there is a 1 1 2 ridge board nailed into the wall and the width of the lean to is 96 then the run will be 94 1 2 96 1 1 2 94 1 2.
Jul 21 2018 mar 28 2019.
Thus a 4 12 pitch would be a 33 slope.
However rise over run is more efficient and easier to understand for the average diyer.
Some may say it is ugly.
If the lean to is enclosed on the low eave side the new lean to roof outside columns must now carry the wind load against the top half of the new wall plus the entire roof.