Building components · Frame Members
Collar Tie
Explains the collar as a tie whose position along the rafters determines how effective it is.
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 collar is
A collar connects a pair of opposing rafters somewhere above their feet, holding them together. It resists the roof's tendency to spread outward, which is the same problem a ceiling joist acting as a tie addresses at a lower level.
Where it sits matters a great deal. A collar close to the rafter feet works much like a full tie; one placed high, near the ridge, resists spread much less effectively and changes the forces in the rafters themselves.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a ceiling joist. A ceiling joist ties at plate level and also carries a ceiling; a collar is higher up and commonly carries nothing.
- It is not a purlin. A purlin supports rafters vertically; a collar ties them horizontally against spreading.
- It is not a ridge member, though collars are sometimes confused with them because both are near the apex.
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.
- collar
- collars
- collar beam
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Its height above the rafter feet, which governs how much of the spreading force it actually resists.
- Its connections to both rafters, since a tie is only as good as its fixings.
- Whether anything else is resisting spread at a lower level.
- What the roof structure was designed to do, since collars are part of a scheme rather than an addition that works in isolation.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
A collar carries tension, and how it is fixed at each end is therefore central rather than incidental.
Roofs where the tie action is inadequate spread at the eaves, and the walls beneath show it.
Collars are frequently in the way in loft conversions, and raising or removing them changes the structural scheme.
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.
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 a collar can be raised freely to gain headroom. Its position determines its effectiveness, and raising it changes the forces throughout the roof.
- That adding collars fixes a spreading roof. Whether it does depends on the whole structural arrangement, including what is happening at the feet.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What is resisting spread in this roof, and what part do the collars play?
- Does any proposed change to collar height alter the structural scheme?
- How are the collars fixed to the rafters, and are those fixings intact?
- Is there evidence of spread at wall head level?
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 height, section, spacing or fixing is stated here.
- Raising, removing or adding collars 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 →