A ridge board is a spacer. A ridge beam is a structural member. They sit in the same place at the top of a roof and look almost identical from a ladder, but only one of them is holding anything up, and confusing the two is one of the more expensive mistakes in residential framing.
The difference comes down to a single question: what stops the rafters from pushing the walls apart?
Why a Sloped Rafter Pushes Outward
A flat joist under load simply bends. A sloped rafter does something else: the load running down the slope tries to slide the rafter outward at its base. That horizontal push is called thrust, and it is what wants to spread the top of the walls.
A roof has two ways to deal with it. Either something ties the two sides together near the bottom so the rafters cannot spread, or something holds the top up so the rafters never lean on each other in the first place. Which one you choose decides whether you have a ridge board or a ridge beam.
Ridge Board: a Spacer, Not a Support
In a conventionally framed roof the rafters on each side bear against each other at the peak. The board between them keeps them aligned, gives a surface to nail to and sets the spacing, but it is not carrying vertical load down to anything. Remove it in your head and the rafter pair still stands, as long as the bottoms cannot spread.
That last clause is the entire design. The thrust has to go somewhere, and in a conventional roof it goes into the ceiling joists or rafter ties running across the building near the plate line. Those members are in tension, working like the bottom chord of a truss.
Which is why a ridge board only works when the ties are present and properly connected. Cut the ceiling joists to open up a vaulted space and you have removed the thing that was holding the walls together, even though you never touched the roof itself. The walls lean, the ridge drops, and the drywall cracks in the corners.
Ridge Beam: a Beam That Holds the Roof Up
A ridge beam carries load. The rafters bear on it rather than against each other, so each rafter behaves like a simple sloped member spanning from the wall to the ridge. No opposing pair, no thrust, no need for ties across the building. That is what makes a cathedral ceiling possible.
The catch is that the load has to keep going. A ridge beam collects half the roof and has to deliver it to posts at each end, and those posts have to land on something continuous all the way to the foundation. A ridge beam supported on a wall that is itself supported on nothing in particular has just moved the problem down a story.
| Ridge board | Ridge beam | |
|---|---|---|
| Carries vertical load | No | Yes |
| Rafters | Bear against each other | Bear on the ridge |
| Thrust at the walls | Yes, must be tied | None |
| Needs ceiling joists or rafter ties | Yes | No |
| Needs posts and a load path below | No | Yes, at both ends |
| Allows a vaulted ceiling | No | Yes |
| Typical material | Nominal lumber, often 1x or 2x | LVL, glulam, a steel beam or a flitch beam |
Because a ridge beam can collect a long run of roof, it often ends up as engineered lumber or steel rather than sawn timber. Where headroom is tight, a flitch beam gets the capacity into the depth available, and where the span is long a rolled section from the wide flange beam sizes chart may be the simpler answer.
Which One Does the Code Require?
It is not a free choice. Building codes tie it to roof slope and to whether the ties are there, on the reasoning above: a shallow roof generates far more thrust for the same load, and at some point ties stop being a practical way to resist it.
Timber design in the United States runs through the American Wood Council, whose standards are developed in an ANSI process and referenced in the I-Codes and cover wood design in residential and commercial construction (checked September 2026). Rafter sizing itself comes off span tables for the species and grade in use; AWC publishes a free Span Options Calculator for joists and rafters covering the species and grades in the NDS Supplement (checked September 2026).
Note what those tables give you: the rafter. They do not size the ridge beam, because that depends on the roof area it collects, the snow load and the span between posts.
How This Goes Wrong in Remodels
The classic sequence: someone wants a vaulted ceiling in an existing house, the ceiling joists are in the way, so they come out. The roof was designed as a ridge board roof relying on those joists. Nothing collapses that afternoon, which is the dangerous part, but the walls begin to spread and the ridge sags over months.
Doing it properly means replacing the ties with a real ridge beam, sized for the roof it now carries, with posts and a load path down to the foundation. That is the same class of work as removing a load-bearing wall: a structural change that needs a design, a permit and an inspection, not a weekend.
Frequently Asked Questions
How do I tell which one my roof has?
Look at the depth and at the ends. A ridge board is usually just deep enough to catch the cut ends of the rafters and dies into nothing in particular. A ridge beam is noticeably deeper, often engineered lumber or steel, and lands on posts. If there are ceiling joists or rafter ties across the space, it is almost certainly a board.
Can I remove ceiling joists if I add collar ties?
Collar ties near the ridge are not the same as rafter ties near the plate. They resist a different action, and moving a tie up the slope greatly increases the force in it. This is a calculation, not a substitution.
What size ridge beam do I need?
It depends on the span between posts, the width of roof it collects, the snow and wind loads, and the material. There is no table that answers it from the room dimensions. A licensed structural engineer sizes it.
Is a ridge beam always bigger than a ridge board?
In practice yes, usually much bigger, because it is carrying half the roof rather than nothing. Size alone is not proof though. What makes it a beam is that the rafters bear on it and it has posts under it.
Can a steel beam be used as a ridge beam?
Yes, and it is common where the span is long or the depth is limited. It brings the usual steel considerations: connections, a nailer for attaching the rafters, weight during erection and corrosion protection if it is ever exposed.
The Short Version
A ridge board spaces rafters that lean on each other, and the thrust is held by ties across the building. A ridge beam holds the rafters up, removes the thrust entirely, and needs posts and a continuous load path to the foundation. You cannot turn one into the other by cutting the ceiling joists, and which one a given roof needs is a question for a licensed structural engineer.
Reference information only, not engineering advice. Disclaimer.