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Long SFS walls need movement joints. Without them, walls crack, boards split, and finishes fail. Movement joints aren't complicated, but they're easy to miss — and the consequences of missing them can be expensive. This guide explains when you need movement joints in SFS walls, how far apart to space them, and how to detail them correctly.

What is a movement joint?

A movement joint (sometimes called an expansion joint or control joint) is a deliberate gap in the SFS wall that allows the wall to expand and contract without cracking. Movement joints in SFS walls are typically horizontal or vertical gaps of 10–20mm between sections of wall, sealed with a flexible sealant or covered with a cover strip.

Unlike deflection heads (which are at the top of the wall and accommodate movement of the structure above), movement joints are within the wall itself — they break the wall into segments so each segment can move independently.

Why long walls need them

SFS walls expand and contract for several reasons:

• Thermal movement — steel expands when heated and contracts when cooled. A 20°C temperature change on a 20m wall can cause 5mm of movement.
• Moisture movement — board materials (plasterboard, OSB, sheathing) expand and contract with humidity changes.
• Structural movement — the primary structure deflects under load, and this movement is transferred to the wall unless accommodated.
• Foundation movement — small settlements can introduce cracks in long walls.

Without movement joints, these movements create stress in the wall. Eventually, the stress exceeds the strength of the boards or the joints between them, and cracks appear. Movement joints allow the stress to be released in a controlled way.

When movement joints are required

Movement joints in SFS walls are required:

1. At specified intervals along long walls

The most common trigger. Walls exceeding a certain length need joints at regular intervals. The interval depends on the type of SFS, exposure, and the specific project requirements. Common guidance is every 6m, 8m, or 10m — see below.

2. At junctions with structural elements

Where an SFS wall meets a concrete column, steel beam, or other structural element, a movement joint may be required. The wall moves independently of the structure, and the joint accommodates that movement.

3. At changes in wall height or thickness

Where the wall height changes (e.g. at a step in the building) or the thickness changes (e.g. where a structural wall meets a partition), a movement joint may be required.

4. At changes in substrate or supporting structure

Where the wall transitions from one type of substrate to another (e.g. from concrete slab to steel frame), the different thermal and structural behaviour may require a movement joint.

5. At building expansion joints

Where the building itself has an expansion joint, the SFS wall must have a matching movement joint at the same location.

Joint spacing guidance

The correct spacing depends on several factors, but as a starting point:

These are general guidance. For any specific project, check with the manufacturer, the structural engineer, or the cladding/board supplier — they may have specific recommendations based on the build-up.

Types of movement joint

Simple gap with flexible sealant

The most basic movement joint is a 10–20mm gap between sections of wall, sealed with a flexible fire-resistant sealant. This works for internal walls with painted or wallpapered finishes.

Cover strip or trim

A gap covered by a trim — PVC, aluminium, or timber. The trim hides the gap and allows it to close and open invisibly. Common in commercial and domestic finishes.

Proprietary movement joint profile

Manufactured profiles designed specifically for movement joints — typically metal or PVC sections with flexible sealant built in. These are used in high-specification applications and in fire-rated walls where the movement joint must also maintain fire performance.

Fire-rated movement joints

For fire-rated walls, the movement joint must maintain the fire rating of the wall. Fire-rated movement joint profiles (often intumescent-based) are used. The joint must allow movement under normal conditions but seal in a fire.

Acoustic movement joints

For acoustic-rated walls, the movement joint must maintain the acoustic performance. Acoustic sealants and profiles are used.

How to detail and install

1. Plan the joint locations

Mark out movement joint locations on the installation drawing. Determine spacing based on the wall length, finish, and any structural movement.

2. Interrupt the framing at the joint

At the joint location, don't run the SFS framing continuously. Stop the studs and track on one side of the joint, and start a new frame on the other side. This may mean two head tracks and two base tracks at the joint, or a single track with a deliberate break.

3. Stop the boards at the joint

Boards should stop 10–20mm short of the joint on both sides. Don't run boards across the joint — they'll crack when the joint moves.

4. Fit the joint profile or sealant

If using a proprietary profile, fit it according to the manufacturer's instructions. If using sealant, apply flexible fire-rated or acoustic sealant (as required) to fill the gap.

5. Finish over the joint

If using a cover strip, fix it over the joint. If not, the sealed gap becomes the visible finish. Make sure the finish detail is consistent with the rest of the wall.

6. Coordinate with other trades

Movement joints must be continuous through the wall build-up — through cladding, insulation, boards, and finishes. Coordinate with other trades so joints are aligned.

Common mistakes

No joints on long walls

The most common mistake. Walls over 10m with no movement joints will crack. The cost of retrofit joints (chasing into boards, patching, refinishing) is far higher than including them from the start.

Joints in the wrong location

Placing joints at structural features rather than at planned intervals, or missing joints at changes in wall height or substrate.

Board run through the joint

Running boards continuously across the joint. The joint can't function if it's bridged by rigid material.

Incorrect sealant

Using rigid (cement-based) sealant instead of flexible sealant. The joint must be able to move; rigid sealant will crack.

No fire rating

Using standard sealant in a fire-rated wall. The joint must have a fire-rated sealant or profile to maintain the fire separation.

Not coordinated with cladding

Movement joint in the SFS but not in the cladding — cladding cracks or bulges as the SFS moves behind it.

Missing joints at junctions

Not placing joints where the wall meets structural elements. The wall moves differently from the structure, and this movement causes cracks at the junction.

Summary

Movement joints allow long SFS walls to expand, contract, and accommodate structural movement without cracking. They're required at specified intervals along long walls, at junctions with structural elements, and at changes in wall height, thickness, or substrate. The correct spacing depends on the wall type and finish, typically every 6–10m for standard walls, 3–4m for tiled finishes.

Movement joints must be planned from the start, interrupted through all layers (framing, boards, cladding, finishes), and detailed appropriately for fire and acoustic performance where required.