Because the ridge board is a smaller member typically only an inch thick sometimes even less it is not a structural member and doesn t carry the gravity load.
Gable roof without ridge board.
In this design the tops of the rafters attach to a load bearing ridge beam that runs along the length of the roof.
A ridge board isn t a beam per se.
It s often just a nice way to bring the rafters together.
The typical gable roof diagram above shows the r length measured from the outside wall to the middle of the ridge beam the rafter section diagram below typical of a shed or patio cover roof shows the r length measured from the outside wall to the outside face of the ridge beam either one is acceptable depending on which type of roof you are building but if you are using the.
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 the building.
A proper beam would have a supporting post at each end.
For 2 x 6 rafters use a 2 x 8 ridge board and so on.
Ridge beam sizing is based on the span of the beam between supports and the amount of roof load supported by the beam.
Framing a gable roof building a gable with barge end purlin struts and collar ties.
Ridge board the engineering principles of the ridge board are a bit more complicated.
Putting it together is relatively straight forward if you have basic carpentry skills and use precise measurements.
You don t need a ridge beam but you do need a way to keep the walls from spreading.
The picture above shows the plan view of a gable roof ladder trusses are made up using four noggins bridging at each corner to support a rafter outside the building.
That rafter outside forms the overhang for the barge boards to fix to and so the soffit boards and ventilation are continuous all the way.
A ridge board is a non structural member that serves as a prop for opposing rafters to rest against and connect to.
A structural ridge is the standard alternative to ceiling joists.
Ridge beams are required by code if the roof slope is less than 3 in 12 irc section r802 3.
Its only job is to provide a connection point for the roof joists on each side of the roof.
The ridge board s length will be the outside measurement of the building plus the length of the overhang at both ends.
To build your gable roof you ll need wooden boards cut into joists rafters supports and a ridge board in addition to sheathing felt paper and shingles.