What Is a Ridge Beam vs. Ridge Board?
A ridge beam is a structural beam at the roof peak that carries the rafters' vertical loads to the gable ends or posts — sized by engineering for bending and deflection. A ridge board is a non-structural board that rafters merely nail to, with the roof's thrust resisted by ceiling joists or collar ties instead. Confusing the two is a classic framing error: a ridge board installed where a ridge beam is needed lets the roof spread and sag.
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Ridge beam (structural)
The beam carries half the roof load (each rafter delivers its top reaction to the ridge), spanning between supports — gable-end walls, posts, or interior bearing walls. Engineered lumber (LVL, glulam) or steel for typical spans; sized for bending, shear, and deflection. The rafters connect with hangers or engineered connections (not toenails alone). Vaulted and cathedral ceilings need ridge beams because there are no ceiling joists to tie the rafters.
Ridge board (non-structural)
The board (typically 1x or 2x) is just a nailing surface — the rafters' outward thrust is resisted by ceiling joists acting as ties across the building, forming the triangle that keeps the roof from spreading. This only works with a complete tie system: ceiling joists at every rafter pair (or engineered alternatives like collar ties plus structural ridge). Cut the ceiling joists for an attic room without adding a ridge beam, and the roof spreads.
What fails
The failure pattern: a homeowner removes ceiling joists or adds a vaulted ceiling keeping the original ridge board — the ridge sags, the walls bow outward, drywall cracks at the wall-ceiling joint. The fix is retrofitting a structural ridge beam (major work: temporary shoring, beam installation, new supports to the foundation). On framing inspections, the checker verifies which system the plans show and that the ties or beam match.
The bottom line
Ridge beams carry roof loads (needed for vaulted ceilings); ridge boards are just nailing surfaces relying on ceiling-joist ties. Never remove the ties without adding the beam.
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