A ridge board was not always required and the photo above of the attic in a 1920s era house shows a roof framed without one.
Roof without ridge board.
A structural ridge is the standard alternative to ceiling joists.
Its only job is to provide a connection point for the roof joists on each side of the roof.
In conventional gable roof framing the slope of the roof is formed by rafters that run diagonally downward from the peak of the roof to the tops of the exterior walls of.
For 2 x 6 rafters use a 2 x 8 ridge board and so on.
You don t need a ridge beam but you do need a way to keep the walls from spreading.
Ridge beam sizing is based on the span of the beam between supports and the amount of roof load supported by the beam.
One collar tie would be enough in your case.
This can be accomplished with collar ties boards spanning the shed at ceiling height or with large gussets further up the rafter slope.
Rafters and ridge boards.
A ridge board is a non structural member that serves as a prop for opposing rafters to rest against and connect to.
For 2 x 4 rafters use a 2 x 6 ridge board.
This video shows how to make roof rafters with a rafter square and or a speed squ.
In most applications the ridge board is not structural and only serves as a convienience for the carpenters as they frame the roof.
You may splice two boards together to achieve this length if necessary using a 14 and 1 2 inch block of the same material.
In this design the tops of the rafters attach to a load bearing ridge beam that runs along the length of the roof.
While the joists commonly attach to the side of a ridge beam they can also sit on top of it as shown in the diagram below which creates an interesting look.
First off yes it is a common practice to frame a roof with no ridgeboard.
The ridge board s length will be the outside measurement of the building plus the length of the overhang at both ends.
Ridge board the engineering principles of the ridge board are a bit more complicated.