A classic example of the exposed ridge beam structure can be seen on our magnolia residence which is currently in construction.
Roof ridge beam.
The loads on the ridge beam are carried by vertical posts at the beam ends down through the building structural walls to the building foundation.
Ridge beam sizing is based on the span of the beam between supports and the amount of roof load supported by the beam.
With this design the ridge beam bears much more load weight than the ridge board on a standard stick framed roof.
Yes either a ridge board or a ridge beam is necessary and required by the building code where roof rafters meet at the the center of their span.
A timber frame roof has rafters and a ridge beam as with stick framing but the ridge is a large structural beam that the rafters sit on top of or sometimes fit into notches cut into the beam.
The difference between them is that a ridge beam is a structural member that bears half of the live and dead loads of the rafters on either side of it but a ridge board is not structural.
I always always build trusses.
Now if you have done any looking around this site you ll quickly see that i am not a fan of using a ridge beam in shed construction.
Framing in a ridge beam in shed roof construction is not hard.
The ridge beam is typically a larger member like a 4 x 12 and carries the gravity load of the roof joists just as the bearing wall or header does at the envelope.
Ridge beams are required by code if the roof slope is less than 3 in 12 irc section r802 3.