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Corners are where SFS walls most often go wrong. Internal and external corners are the points where two walls meet, and getting them right is essential for the structural integrity, fire performance, and finish quality of the whole wall system. This guide explains how to detail every type of SFS corner correctly.

Why corners matter

Corners are structurally important because:

• They carry load — in loadbearing walls, the corner is where load from two walls meets and is transferred to the floor below
• They're rigid points — corners are the stiffest part of an SFS wall, and they need to be detailed so that the rigidity doesn't transfer bad stresses to the boards
• They're fire-critical — corners are where fire can bypass the fire separation if not detailed correctly
• They're visible — corners are seen and touched, and any imperfection shows up
• They're where board joints concentrate — board joints at corners are common weak points for cracking

Every corner should be detailed on the installation drawings, with the stud layout, track runs, and board pattern shown clearly.

Internal corners

An internal corner is where two walls meet at an angle less than 180° — like the corner of a room. It's the most common corner type in SFS construction.

Stud layout

There are two common approaches:

• Two studs meeting at the corner — a stud on each wall, positioned so they meet at the corner with their flanges overlapping. This is the simplest and most common approach.
• Double stud at the corner — two studs on one wall, back-to-back, with the second wall's stud meeting the face of the double stud. This is more rigid and is often used in fire or acoustic walls.

Track runs

The base track runs continuously around the internal corner, with the two walls meeting cleanly. The head track does the same.

At the corner, the track from one wall meets the track of the other. They should butt cleanly with no gap. If the corner is not square, the tracks may need to be mitred (cut at an angle) to meet cleanly.

Fixing

Fix the two corner studs together using tek screws through their flanges. This makes the corner a single rigid unit.

Fix the base track and head track to the floor and soffit as normal (600mm centres), plus an extra fixing near the corner for stability.

Board pattern

Boards should not be continuous around an internal corner. Instead:

• Board from one wall runs to the corner, stopping at the inner face of the corner stud
• Board from the other wall runs to the corner, stopping at the inner face of its corner stud
• The joint at the corner is filled with jointing compound and tape

This creates a "butt joint" at the corner. It's the standard detail for internal corners.

External corners

An external corner is where two walls meet at an angle greater than 180° — like the outside corner of a building. It's less common in internal partitions but very common in SFS external walls.

Stud layout

The most common approach is:

• Two studs meeting at the corner — a stud on each wall, positioned so they meet at the external corner with their webs facing outward
• Corner post — sometimes a separate corner post (a square or rectangular section) is used to make the corner more rigid
• Corner box — for very rigid corners, a small box section of track or stud is formed at the corner

Track runs

The base and head tracks run continuously around the external corner. Because the corner "sticks out", the tracks have to follow the external profile — this means the track flanges are on the outside of the corner, facing outward.

Where two tracks meet at the external corner, they should be mitred and fixed together (using a corner bracket or corner piece) to make a continuous, rigid corner.

Fixing

Fix the corner studs together with tek screws. For external corners, it's often best to use a corner bracket or L-bracket to reinforce the corner.

Fix the tracks at the corner with extra anchors — the external corner is a vulnerable point for wind loading.

Board pattern

At external corners, the board detail depends on the finish:

• Boarded corner — one wall's boards run past the corner and finish flush with the outside face of the other wall. This creates a clean external corner without a visible joint. The boards of the second wall butt into the back of the first wall's boards.
• Corner bead — a metal or plastic corner bead is fitted over the corner, and boards on both sides butt into the bead. The corner bead provides a clean, rigid edge that protects against impact damage.

For plasterboard external corners, a corner bead is almost always used — it protects the corner from damage and provides a clean finish.

T-junctions and K-junctions

A T-junction is where one wall meets another at 90° — like a partition ending against a main wall. A K-junction is where a wall meets another at an angle (not 90°).

T-junction

At a T-junction, the stud of the meeting wall is fixed to the face of the wall it meets. Typically:

• A stud on the meeting wall is positioned with its web against the face of the main wall
• The meeting wall's track butts into the main wall's face
• Boards on the meeting wall stop at the main wall face

K-junction

Similar to a T-junction but at an angle. The meeting wall's track and studs are cut at the angle to fit against the main wall.

Fire and acoustic consideration

At T-junctions, the junction between the two walls is a potential path for fire and sound. If either wall is fire-rated, the junction must be sealed with fire-rated sealant or a fire-stop. Similarly for acoustic-rated walls.

Board patterns at corners

Board patterns at corners are critical for avoiding cracks. The main principles:

Stagger board joints

If two boards meet at a corner, the joint on one face should not align with the joint on the adjacent face. Stagger the joints by at least 300mm.

Don't wrap boards around corners

As noted above, wrapping boards around corners causes cracking. Always cut and joint at the corner.

Use a corner bead for external corners

Corner beads (metal or plastic) provide a clean edge, protect against impact, and hide the joint between the two boards.

Double board at high-stress corners

In fire-rated or acoustic-rated walls, corners are often double-boarded (two layers) to maintain the fire or acoustic performance at the corner. Check the tested system.

Don't leave gaps

Gaps at corners are a fire and acoustic weakness. Fill any gaps with intumescent sealant or fire-stop before finishing.

Fire and acoustic performance

Fire

At fire-rated corners, the joint between the two walls must be detailed so that fire can't bypass the fire separation. This typically means:

• Fire-rated board at the corner (same specification as the walls)
• Fire-rated sealant in any gaps
• Cavity barriers at the corner if the cavity is continuous
• Tested corner detail if the wall system is fire-rated

Acoustic

At acoustic-rated corners, the junction between the two walls is a potential path for flanking transmission. Acoustic sealant at the junction, and careful detailing to avoid gaps, maintains acoustic performance.

Finishing the corner

After boarding, corners need to be finished:

Internal corners

• Fill the joint with jointing compound
• Embed joint tape into the compound
• Skim over the tape with more compound
• Sand smooth

External corners

• Fit corner bead (metal or plastic)
• Fix bead with screws or adhesive
• Fill over the bead with jointing compound
• Sand smooth

Painting or finishing

After sanding, the corner is ready for paint, wallpaper, tiles, or other finish. Corner beads provide a clean, sharp edge that takes paint well and resists damage.

Common mistakes

Wrapping boards around corners

Causes cracking at the bend line. Always cut and joint.

Not staggering joints

Joints aligning across adjacent faces concentrate stress and crack.

Missing corner bead on external corners

Leaves a fragile edge that gets damaged and looks poor.

Not fixing corner studs together

Corners become flexible, causing movement and cracks.

Gaps at fire-rated corners

Fire can bypass the fire separation. Fill with fire-rated sealant.

No acoustic sealant at acoustic corners

Flanking transmission compromises acoustic performance.

Wrong stud layout at external corners

Doesn't provide enough rigidity. Use corner bracket or box detail.

Not shown on drawings

Installers guess, and different installers detail differently. Always show corner details on installation drawings.

Summary

SFS corners are structural, fire, acoustic, and finish-critical. Internal corners use two studs meeting, butt-jointed boards, and filled joints. External corners use two studs meeting, corner brackets for rigidity, corner beads for protection, and cut boards (not wrapped). T-junctions and K-junctions need careful detailing for fire and acoustic performance.

Get corners right and the whole wall works. Get them wrong and cracks, fire failures, and acoustic compromises appear — often after the project is finished.