Building components · Frame Members
Queen Post
Explains the queen post as a paired position whose defining consequence is the space it does not occupy.
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 queen post is
Queen posts come in pairs. Each stands between the tie below and the sloping member above, set back from the centre line, and the pair is commonly connected across the top by a horizontal member so that the heads are held apart as well as held up. The arrangement divides the truss into a central bay and two outer ones.
What makes the position worth naming is the consequence of the pair. A single central member fills the middle of a roof; a pair leaves it open, which is why the form recurs wherever the centre of a roof space has to be usable or a wide opening has to be spanned. The heads of the posts also commonly become the points at which purlins are supported, so the position does structural work in two directions at once.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a king post. A king post is single and sits on the centre line, filling the middle of the truss; queen posts are a pair set either side of it, and the clear space between them is the reason the form is chosen.
- It is not a collar tie. A collar runs between two opposing rafters and is worked by their tendency to spread; the member connecting queen post heads runs between the two posts and is worked by their tendency to be pushed together, which is why the two members look alike and are loaded in opposite senses.
- It is not a roof strut. A strut is commonly inclined and takes purlin load down to a loadbearing wall or binder beneath the roof; a queen post is vertical and works between its own truss's chords, even where a purlin happens to be carried at its head.
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.
- side posts
- paired truss posts
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The member connecting the heads of the pair, since without it the two posts are not acting as the arrangement assumes.
- The joints at the head and the foot of each post, which determine whether the position works in compression, in tension or in both.
- Whether purlins bear at the heads, which adds a duty the post's own joints have to accept.
- The truss being treated as a designed whole, because the outer bays and the central bay behave differently and each depends on the others.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Load arrives at the head of a queen post from more than one direction where a purlin is carried there, and each of those paths passes through the same joint.
The clear central bay is the part of a queen post roof most likely to be built into or opened up, and work there commonly meets the member connecting the two heads.
Spread at the feet of a roof shows in the walls beneath, and whether a queen post arrangement was resisting that spread is a question about the whole truss rather than about either post.
Feet of posts sit on the tie where debris and moisture collect in an unventilated roof space, and the condition of that joint is not readable from the exposed faces.
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.
Related elements
Neighbouring components
Typed relationships to other elements. There is deliberately no generic “related” category: an edge that cannot be classified does not exist.
Clarifications
Commonly misunderstood
- That the two posts are independent members that happen to be in the same truss. They work as a pair with whatever connects their heads, and altering one changes the other.
- That the clear bay between them is structurally spare space. The bay is clear because the arrangement was designed that way, and building into it can change what the posts and the tie are doing.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What connects the heads of these posts, and is that member intact?
- Are purlins carried at the heads, and where does that load go from there?
- Does any proposed work in the central bay alter what the truss relies on?
- How are the feet of the posts joined to the tie, and what condition are those joints in?
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
- This entry describes a position within a truss. It states no section for the posts or for the member connecting their heads, and no span, spacing or capacity, and none can be inferred from it.
- Altering, removing or building into a truss arrangement 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 →