Building components · Frame Members
Deflection Head
Explains the head of a partition as a designed movement condition, distinct both from an ordinary head track and from a movement joint between two elements that each move.
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 deflection head is
A deflection head is the arrangement at the top of a non-loadbearing partition that allows the structure above it to move without pressing on the partition. It is commonly formed with a deep-legged head track that locates the studs laterally while leaving them free vertically, together with the gap above the linings that the expected movement requires.
It matters because a partition built tight to the soffit becomes a prop. Floors and beams deflect under load and go on deflecting over time, and a partition standing in the way takes load it was never arranged for: studs bow, boards crack along the head line, and doors within the partition bind. The deflection head exists to make that impossible while still keeping the head closed where the partition has to separate.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a movement joint. A movement joint is a discontinuity between two parts of a construction that both move and that must be free to move relative to each other; a deflection head is a one-sided condition in which the structure above moves and the partition beneath must not be made to follow it.
- It is not a partition track in general. Every framed partition has a track at head and base; a deflection head is the particular head arrangement that permits vertical movement, and a partition can have a perfectly ordinary head track and no deflection head at all.
- It is not a head seal or a cavity barrier. Those close a gap; a deflection head has to close a gap that is required to keep changing, which is a different problem and is why the two are detailed together rather than treated as one.
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.
- movement head
- slip head
- sliding head detail
- head deflection detail
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- How much the structure above is expected to move, which is a design quantity established for the building rather than a property of the partition beneath it.
- Whether the partition has to separate in fire or acoustic terms, since the head has to stay closed throughout the whole range of movement it allows.
- What is fixed to or built into the partition near its head, because anything spanning the gap reinstates exactly the restraint the detail exists to remove.
- The linings, since the boards have to stop short of the structure above and the finish at the head has to accommodate a joint that moves.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The head is the one place a non-loadbearing partition and a moving structure meet, and it is where the consequences of getting that wrong appear, as cracking along a line rather than as anything structural.
Where the partition is fire-separating, the head has to go on separating while remaining free to move, which is a tested arrangement rather than something settled on site.
An open head is a direct path over the partition, so the detail has to be both free to move and closed to sound, and those two requirements pull against each other.
The gap the detail depends on is invisible once the partition is lined, and it is commonly lost to a screw through both legs of the track, a service bracket, or a board fixed hard to the soffit.
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.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
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 cracking along the top of a partition is a decorating problem. It is commonly the visible result of a head that is restraining, or being loaded by, the structure above it.
- That the studs can be screwed off through the head track for stability. Fixing them vertically reinstates the restraint the deflection head exists to remove, and the detail then does nothing.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- How much movement is the structure above this partition expected to undergo?
- Does this partition have to resist fire or sound, and how is the head detailed to do that while still moving?
- How are the studs located at the head without being fixed vertically?
- What crosses the head — services, framing, door frames, ceiling components — and does any of it bridge the gap?
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 in a partition. It states no gap, movement allowance, track dimension, fixing arrangement or fire rating, and none can be inferred from it.
- Deflection head details in fire-separating construction form part of a tested assembly, and both the movement allowance and the head arrangement are determined for the building by its design team.
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 →