Who this guide is for
- Owners seeing repeated cracking along the top of an internal wall
- Anyone specifying partitions beneath a concrete or timber floor above
- People supervising a fit-out where partition heads are about to be closed
- Readers preparing questions for a structural engineer about movement
- Anyone writing a handover note about details that must not be filled
Two requirements at one point
The head connection holds the top of the partition laterally while leaving it free vertically. It is asked to do one thing and refuse another at the same place, which is why it is commonly formed as a deep-legged head track that locates the studs laterally without gripping them, together with a gap above the linings.
In masonry the same contradiction appears as a restraint with a gap. Build the wall hard up to a soffit that will deflect and only two things can follow: the wall begins carrying load nothing designed it for, or the finish and the junction crack as the soffit comes down onto it.
How much movement, and who says so
How much the structure above is expected to move is a design quantity established for the building, not a property of the partition beneath it. A cast plate goes on moving after it is built, so the gap left above a partition beneath it is an allowance for something that has not finished happening.
That number comes from the frame designer rather than being assumed, and it is the figure the finishing detail at the head has to respect. This page states none, because the allowance belongs to the specific building.
The ways the gap is lost
The detail depends on a gap that is invisible once the partition is lined, and it is commonly lost without anybody deciding to lose it. A screw driven through both legs of the head track fixes the studs vertically and reinstates exactly the restraint the arrangement existed to remove.
Anything spanning the gap does the same thing: a service bracket, a packer, a board fixed hard to the soffit, a rigid fillet applied at the head line for a clean edge. None of them looks like a change to the structure of the wall.
- A fixing through both legs of the head track
- A bracket or clip spanning the head gap
- Boards taken hard up to the soffit rather than stopped short
- A rigid filler used to tidy the line before decoration
Closing a gap that has to keep changing
Where the partition also has to close the line — against air, against sound, or where separation has been determined by others — the head has a further problem: it has to stay closed throughout the whole range of movement it allows. A joint closed with a flexible sealant over backing stays continuous while the construction either side shifts.
A joint packed hard or filled solid closes the same gap by bridging it, and at a head that turns the abutment into a route for load into the partition. The two outcomes look identical from the room.
Glazed screens, where the consequence is immediate
A glazed screen makes the same failure visible faster. The base carries weight and sets the line; the head restrains and must not carry anything. If the head closes up, the glass begins taking load through its edge, and the failure appears in the panel rather than in the detail that caused it.
That is also why filling or packing a screen's head allowance is treated as a caution rather than a workmanship preference.
What to say on site, and what to leave behind
The people who close a head gap are rarely the people who specified it, and the instruction they are working to is usually about appearance. A note on the drawing explaining that the gap is a movement allowance, rather than a tolerance to be taken up, is the cheapest intervention available.
After handover the same information matters again, because a later fit-out will fix brackets, trims and services at exactly that line.
Partition head checklist
- 1Ask what movement the structure above this partition is expected to impose
- 2Confirm who provided that figure and where it is recorded
- 3Establish whether the head is an ordinary track or a movement-accommodating arrangement
- 4Check whether the partition is required to stay closed at the head as well as free to move
- 5Confirm boards stop short of the structure above rather than butting it
- 6Look for fixings driven through both legs of the head track
- 7Check for brackets, packers or services spanning the head gap
- 8Confirm what closes the gap, and that it can take repeated movement
- 9Ask who is applying the finish at the head and what they have been told
- 10Note the head detail on the drawing as a movement allowance, not a tolerance
- 11Record the detail in the handover information for later fit-out
- 12Where cracking recurs along one line, have the head examined rather than redecorated
Common mistakes to avoid
- Reading the head gap as an untidy joint to be filled
- Screwing studs off through the head track for stability during installation
- Filling the gap with the same rigid material used on the wall face
- Assuming cracking along the top of a partition is a decorating problem
- Fixing services or brackets across the head after the wall is complete
- Taking a movement allowance from habit rather than from the structural design
- Packing a glazed screen's head allowance to make a trim line up
When to involve a professional
- How much the structure above a partition will move is a structural determination for the building, made by qualified professionals
- Head details in fire-separating construction form part of a tested assembly and are determined by the design team
- What is required at a junction between separating or fire-resisting elements is a regulated determination, not a site decision
- Whether a head arrangement accommodates the movement expected is confirmed by the designer rather than inferred from the detail
- Recurring cracking along one line is worth having assessed before any further redecoration
Frequently asked questions
Questions readers ask about this topic
Why is there a gap above my partition?
Because the floor or roof above deflects under load and goes on deflecting over time. The gap is the allowance that lets that happen without the partition standing in the way and picking up load it was never arranged to carry.
Is cracking along the top of a wall a decorating problem?
It is commonly the visible result of a head that is restraining, or being loaded by, the structure above it. Redecorating treats the symptom, and the line usually returns, which is why the head detail is worth examining first.
Can the head gap be sealed and still move?
That is exactly what the detail has to achieve. A closure formed over backing can stay continuous while the construction either side shifts, whereas a gap packed hard closes it by bridging it and reinstates the load path the arrangement existed to prevent.
What is different about a masonry partition head?
The same contradiction, with more weight behind it. The wall has to be restrained laterally without being loaded vertically, and the closure at the head is the detail most often replaced on site by simply building the wall tight to the soffit.
Who should be told about the head detail on site?
Whoever closes the line and whoever decorates it, because both arrive after the framing trade has left and both are working to an instruction about appearance. A note on the drawing saying the gap is a movement allowance is the usual way that happens.
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