Building components · Frame Members
Ridge Board
Explains the important distinction between a ridge board that aligns rafters and a ridge beam that carries them.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a ridge board is
The ridge member runs horizontally along the apex of a pitched roof, and the tops of the rafters from each slope meet at it. What it actually does depends on the roof: in some it merely aligns the rafters and gives something to fix against, and in others it carries them.
That difference is the most consequential thing about it. Where opposing rafters are tied at their feet, the pair works as a triangle and the ridge does little; where they are not tied — as in a vaulted or open room below — the ridge has to carry the rafters and becomes a beam.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- A ridge board is not a ridge beam, and the words are not interchangeable. A board aligns; a beam carries. Confusing them is how open-plan roof alterations go wrong.
- It is not a purlin. A purlin supports rafters part-way up the slope; the ridge is at the apex.
- It is not the ridge covering. The tile, capping or flashing along the apex is part of the roof covering, not the structure.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- ridge
- ridge beam
- ridge member
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Whether the rafter feet are tied, because that determines whether the ridge is carrying anything at all.
- What supports it at its ends and, where it is acting as a beam, along its length.
- How the rafters connect to it, which differs between the two cases.
- Any alteration below that removes ties, since that can turn a board into a beam it was never designed to be.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Whether load passes through the ridge or through the tied rafter triangle is the question that determines what the member has to be.
A ridge sagging or the roof spreading at the eaves are related symptoms, and both point at how thrust is being resisted.
Removing ceiling ties to open up a roof space changes the structural action, and the ridge is where that change is felt.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Junctions
Interfaces this element takes part in
Junctions where the condition between this element and another governs how the construction behaves. These name the junction and the subjects it raises; they are not details, arrangements or approved ways of building.
Rafter to Ridge
Where opposing rafters meet at the apex, and where the roof's whole structural action is decided.
Raises: Structural transfer · Movement · Buildability · Thermal continuity
Where it is met
Application contexts
Building contexts where this element is commonly encountered. Association is not recommendation: appearing here does not mean the component suits every instance of that context, or any particular one.
- Pitched Roof
- Superstructure
Clarifications
Commonly misunderstood
- That the ridge holds the roof up. In a tied rafter roof it largely does not; the triangle does.
- That opening up a loft is a finishing operation. Removing the ties that make the rafter pair work is structural alteration, and the ridge is directly affected.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Is the ridge in this roof acting as a board or as a beam?
- Are the rafter feet tied, and does anything proposed remove that tie?
- What supports the ridge, and is that support adequate if the structural action changes?
- What evidence is there of spread at the eaves or sag at the ridge?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- No section, span or capacity is stated here, and the distinction between board and beam cannot be resolved from this entry for any particular roof.
- Opening up a roof space by removing ties is structural alteration requiring qualified design.
Structural Frame Members
The columns, beams, joists, rafters, plates and bracing that make up a load-carrying frame, identified by the position each occupies.
Browse all frame members entries →