A 4 12 pitch is around 18 5 degrees but not exactly.
Minimum roof pitch for dormers.
A shed dormer on the other hand is usually had on homes with a roof pitch of at least 8 in 12 or steeper.
You can also divide the rise over run multiply by 100 and get a percentage.
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.
Pitched roofs can also be used to incorporate roof lights angled in a specific direction or dormer windows.
The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.
However you can only use this pitch with built up roofing or specialized synthetic roofing.
Having a steeper pitched roof allows for more space in a shed loft.
This type of dormer needs a roof pitch shallower than that of the original.