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SFS is a precise, engineered system — and it shows on site. The most common problems we see aren't design failures; they're installation details that were missed, misunderstood, or rushed. This article lists the mistakes we see most often, and how to avoid each one.

1. Using the wrong track size

The track must be 4mm wider than the stud it accommodates. A 70mm stud needs a 74mm track, a 90mm stud needs a 94mm track, and so on.

What goes wrong

• Ordering "70mm track" for 70mm studs — you receive 74mm track (correct) or 70mm track (wrong, won't fit)
• Using 94mm track with 70mm studs — studs are loose, wall is unstable
• Mixing track sizes — 74mm base track with 94mm head track — wall misaligned top and bottom
• Confusing 146mm and 150mm — 146mm stud fits 150mm track, but 150mm stud needs 154mm track

How to avoid it

• Order tracks by actual track width (74mm, 94mm, etc), not by stud width
• State clearly: "74mm track to suit 70mm stud"
• Check the delivery against the specification before starting
• Our SFS Order Builder calculates this automatically

2. Wrong head detail (slotted vs plain)

Infill walls need slotted head tracks (for deflection). Loadbearing walls need plain head tracks (no deflection).

What goes wrong

• Plain track on infill — primary structure deflects, cracks appear in the wall
• Slotted track on loadbearing — wall sinks under load, structural failure possible
• Slotted track but no deflection gap — track can't slide, cracks anyway
• Slotted track but filled with plaster — track can't slide, cracks anyway

How to avoid it

• Confirm on the drawing which type of head is required
• Use slotted track for infill, plain track for loadbearing — every time
• Leave the deflection gap (typically 20–30mm) free — don't fill it
• Don't over-tighten the anchors through the slots

3. Missing or inadequate bracing

Walls need bracing during construction (temporary) and after (permanent). Most permanent bracing comes from the boards, but some walls need additional bracing.

What goes wrong

• No temporary bracing — wall wobbles, studs drift out of plumb, wall topples in wind
• Bracing removed too early — before boards are fitted, wall becomes unstable again
• Missing permanent bracing — tall walls, free-standing walls, and walls with large openings need diagonal strapping or structural sheathing
• Bracing interrupted at openings — openings become weak points

How to avoid it

• Install temporary bracing before starting wall framing
• Brace at the end of every working day
• Only remove temporary bracing once permanent bracing is in place
• Follow the bracing design for tall walls and free-standing walls
• Carry bracing around openings, not through them

4. Poor opening framing

Every opening needs trimmer studs, a lintel, and (for windows) a sill. Getting this wrong is a common source of structural problems and board cracking.

What goes wrong

• Single trimmer studs on standard openings — inadequate for doors and windows over 1m wide
• Trimmer studs not full height — load from above the opening isn't transferred correctly
• Lintel not bearing properly — load pushes the lintel down, wall cracks
• Opening cut to wrong size — window/door frame won't fit, or gaps are too large
• No sill on window openings — window has no support, sags over time

How to avoid it

• Double trimmer studs on all standard openings
• Trimmer studs run full height, base track to head track
• Lintel bears onto the trimmer studs with at least 4 fixings per end
• Opening = frame size + 10mm clearance each side
• Sill on every window opening, at the specified sill height

5. Missing cavity barriers

Cavity barriers prevent fire and smoke travelling through concealed cavities. They're required at junctions, compartments, and openings in fire-rated walls.

What goes wrong

• No cavity barriers at all — fire travels through the cavity, bypassing the fire separation
• Wrong barrier for the cavity — barrier rated for a different cavity width or rating
• Incomplete seals — gaps at ends or joints where fire can pass
• Not around openings — fire bypasses the opening's fire-rated frame
• No documentation — cannot prove compliance when covered up

How to avoid it

• Include cavity barriers on the installation drawing
• Use the correct barrier for the cavity width and rating
• Install continuously — no gaps at ends or joints
• Coordinate with services — fire-stop any penetration
• Photograph before covering up

6. Wrong or missing sealants

Sealant maintains fire, acoustic, and weather performance at junctions. Using the wrong type — or none at all — compromises the wall.

What goes wrong

• No sealant at head/sill — fire and acoustic performance compromised
• Rigid sealant in movement joints — cracks when the joint moves
• Standard sealant in fire-rated walls — doesn't maintain the fire rating
• Missing acoustic sealant — flanking transmission reduces performance

How to avoid it

• Use intumescent sealant in fire-rated walls
• Use acoustic sealant in acoustic-rated walls
• Use flexible sealant in movement joints
• Seal at head, sill, around openings, and at all junctions

7. Board fixing mistakes

The boards are part of the structural, fire, and acoustic performance — not just the finish. Fixing them wrong compromises the whole wall.

What goes wrong

• Fixing centres too wide — boards not structurally part of the wall, bracing lost, fire performance compromised
• Wrong screw length — too short (won't hold) or too long (punctures the boards behind)
• Screws not driven home — screw heads stand proud, board can't sit flush
• Joints not staggered — joints align between layers, cracks concentrate
• Boards fixed to head track — on deflection heads, this prevents the track from sliding

How to avoid it

• Fix at the specified centres — 300mm for fire-rated, 400mm for standard acoustic, 600mm for basic
• Use the specified screw length for the board thickness
• Drive screws just below the board surface — don't break the paper
• Stagger joints by at least 300mm between layers
• Boards stop just below the deflection head track — they don't fix to it

8. Corner detail mistakes

Corners are visible, structural, and fire-critical. Getting them wrong causes cracks, fire failures, and finish problems.

What goes wrong

• Wrapping boards around corners — causes cracking at the bend line
• No corner stud connection — corners become flexible, causing movement and cracks
• No corner bead on external corners — fragile edges that get damaged
• Missing fire-rated sealant at fire-rated corners — fire can bypass the wall
• Not staggered joints at corners — stress concentrates and cracks

How to avoid it

• Cut and butt-joint boards at corners — don't wrap
• Fix corner studs together with tek screws
• Use corner bead on all external corners
• Seal fire-rated corners with intumescent sealant
• Stagger joints on adjacent faces

9. Fire test substitutions

Fire-rated walls are only valid for the exact tested build-up. Substituting anything invalidates the rating.

What goes wrong

• Different board brand — e.g. using Siniat instead of BG Fireline
• Different board thickness — e.g. 12.5mm instead of 15mm
• Different insulation — e.g. PIR instead of mineral wool
• Different stud size or gauge — not matching the tested system
• Different fixing centres — more or fewer screws than tested
• Missing insulation — the cavity is empty when it shouldn't be

How to avoid it

• Read the test report — know exactly what was tested
• Match every component — board, insulation, stud, fixing
• Ask the manufacturer if a substitution is acceptable
• Check the field of application for permitted variations
• Never substitute without written confirmation

Summary

SFS installation mistakes are common, but they're avoidable. The most frequent issues are:

• Wrong track size (remember the 4mm rule)
• Wrong head detail (slotted vs plain)
• Missing or inadequate bracing
• Poor opening framing
• Missing cavity barriers
• Wrong or missing sealants
• Board fixing mistakes
• Corner detail mistakes
• Fire test substitutions

Each of these has a straightforward fix. The key is to plan the detail from the drawing, follow the manufacturer's installation instructions, and check the work at each stage before it gets covered up.