This type of dormer needs a roof pitch shallower than that of the original.
Minimum roof pitch for dormers.
The loft space would be much larger with a roof pitch of 45 degrees.
Having a steeper pitched roof allows for more space in a shed loft.
Pitched roofs can also be used to incorporate roof lights angled in a specific direction or dormer windows.
However you can only use this pitch with built up roofing or specialized synthetic roofing.
You can also divide the rise over run multiply by 100 and get a percentage.
However rise over run is more efficient and easier to understand for the average diyer.
A shed dormer on the other hand is usually had on homes with a roof pitch of at least 8 in 12 or steeper.
The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.
Roofing gutters and all waterproofing anywhere minimum roof pitch i am planning a shed dormer with a roof that will have about 3 12 pitch.