Originally Posted by
Terry Beck
I saw reference to ridge beams as a structural replacment for ceiling joists, but don't understand how that would counteract the spreading forces to the sidewalls.
Terry,
That would be a structural ridge.
In normal construction, the ridge is simply pinched between the two opposing rafters, with the loads trying to go vertically down (by gravity), thereby pushing against the rafters, which in turn push against the tops of the walls, pushing then outward when not supported by shear walls or pilasters or something else.
When a structural ridge is installed, the load of the ridge is carried by the two walls (or columns or something) are each end, then when the rafters are placed, the rafter load is simply carried vertically down from the ends of the structural ridge and vertically down at the walls, with no lateral outward push against the walls (stating it very simply, anyway).
Thus, with a structural ridge, nothing is needed to keep the walls from being pushed out by the roof load. However, something needs to keep the walls from being pushed in or sucked out by wind loads and other loads, so you typically end up with pilasters supporting the wall at specified intervals. The pilasters may be inside, outside, or both.