The Ridge Beam is the horizontal timber beam at the apex of the roof. It has no structural function but is the member against which the high ends of the rafters lean. It ensures that the rafters meet in a straight line and stay upright.
Where a trussed roof is used, the rafters are the top chord of the truss and truss action spans the width of the building. In other cases, the rafters must span from the top of the roof to the top of the walls. The ridge beam supports the rafters at the top of the roof and is a bending member spanning between its supports (generally across rooms).