However rise over run is more efficient and easier to understand for the average diyer.
Pole barn lean to roof pitch.
Thus a 4 12 pitch would be a 33 slope.
A 4 12 pitch is around 18 5 degrees but not exactly.
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.
Lean to shed roofs develop an interesting problem as they get larger.
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.
How to calculate a lean to rafter.
Jul 21 2018 mar 28 2019.
This ugly design is most often avoided by installing a low slope roof to keep the rise of the roof at a minimum.
Some may say it is ugly.
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.
You can also divide the rise over run multiply by 100 and get a percentage.
Enter this measurement into the calculator and select a roof pitch and the length of the rafter will automatically returned along.