Fire Rated Partitions
Fire-rated partitions are one of the most common — and most misunderstood — requirements in SFS construction. Achieving 30, 60, 90 or 120 minutes is not just about adding more board. It requires using a tested build-up, matching every component, and installing it correctly. This guide explains how each fire rating is achieved with SFS, what the boards and insulation have to be, and the common mistakes to avoid.
What is a fire rating?
A fire rating (also called fire resistance) is the period of time a wall can resist the spread of fire and maintain its structural integrity under fire test conditions. It's measured in minutes — typically 30, 60, 90 or 120.
Fire rating is not a single property. It's a combined performance of:
- Integrity (E) — the wall doesn't allow flames or hot gases to pass through
- Insulation (I) — the wall limits temperature rise on the unexposed side
- Loadbearing capacity (R) — the wall maintains structural load (for loadbearing walls only)
For most partitions, the requirement is expressed as EI (integrity and insulation). For loadbearing walls, it's REI. The number before or after the letter is the time in minutes — so "EI 60" means 60 minutes of integrity and insulation.
The test standards
Fire tests on partitions in the UK are carried out to one of two standards:
- BS EN 1364-1 — the current European standard for non-loadbearing partitions
- BS 476 Part 22 — the older British standard, still valid for older tested systems
Both are recognised by Building Control, but BS EN 1364-1 is now the preferred standard for new systems. Loadbearing walls are tested to BS EN 1365-1 (or BS 476 Part 21).
The test result is only valid for the exact construction that was tested. Any change to the board type, thickness, layers, insulation, stud profile, gauge, or fixing method may invalidate the rating.
30-minute fire rating
30-minute fire resistance is the entry-level rating. It's used in low-risk areas — for example, between a domestic room and a corridor, or in some commercial partitions with low fire risk on either side.
How to achieve 30 minutes
The most common 30-minute build-up:
- Board: 1 layer of 12.5mm fire-rated board each side (or 1 layer of 15mm)
- Insulation: Not always required — some 30-minute tests pass without cavity insulation
- Stud: Standard C stud, 70mm minimum
- Gauge: 1.2mm standard
- Centres: 600mm standard
Some 30-minute tested systems use 1 layer of standard wallboard (not fire-rated). This is because the test was conducted with standard board and still achieved 30 minutes. But if the test specifies fire-rated board, you must use fire-rated board.
60-minute fire rating
60-minute fire resistance is the standard rating for most commercial partitions — offices, schools, hospitals. It gives occupants 60 minutes to evacuate in a fire, and contains the fire long enough for the fire service to respond.
How to achieve 60 minutes
Common 60-minute build-ups:
- Board: 2 layers of 12.5mm fire-rated board each side OR 1 layer of 15mm fire-rated board each side (depending on tested system)
- Insulation: Usually required — 50mm or 60mm mineral wool in the cavity
- Stud: 70mm or wider C stud, or I stud depending on tested system
- Gauge: 1.2mm standard
- Centres: 600mm standard
60-minute ratings often start to require specific board types (e.g. BG Fireline, Siniat Fire Board) and specific insulation. The exact build-up must match a tested system.
90-minute fire rating
90-minute fire resistance is used in higher-risk areas — separating walls between commercial units, walls around plant rooms, and some residential separating walls.
How to achieve 90 minutes
Common 90-minute build-ups:
- Board: 2 layers of 12.5mm or 15mm fire-rated board each side
- Insulation: 50mm–100mm mineral wool in the cavity, often with specific density requirements
- Stud: 70mm minimum, wider for taller walls
- Gauge: 1.2mm or 1.5mm depending on tested system
- Centres: 600mm standard, sometimes 400mm
90-minute ratings are more demanding — both in the tested build-up and in the installation quality. A single missing screw, a gap in the insulation, or a poorly fitted board joint can compromise the whole wall's fire performance.
120-minute fire rating
120-minute fire resistance is the highest standard rating. It's used in the most demanding applications — high-rise separating walls, walls protecting escape routes, and industrial fire compartmentation.
How to achieve 120 minutes
Common 120-minute build-ups:
- Board: 2 or 3 layers of fire-rated board each side (usually 15mm), sometimes with specific fire-rated cores
- Insulation: Full-fill mineral wool, 50mm–100mm, often with specific density
- Stud: 90mm minimum, sometimes 100mm or wider
- Gauge: 1.5mm or 2.0mm depending on tested system
- Centres: 400mm or 600mm depending on tested system
120-minute ratings require exact matching to the tested system. Even the fixing centres (screw spacing) can be critical. Any deviation from the tested build-up invalidates the rating.
The role of insulation
Cavity insulation plays a major role in fire performance. It does two things:
- Prevents hot gases circulating in the cavity, which reduces the rate of temperature rise on the unexposed side
- Holds the boards in place as they char and degrade during the fire, maintaining integrity for longer
Not all insulation is equal for fire. Mineral wool (Rockwool, glass wool) is non-combustible and works well. Plastic-based insulation (PIR, EPS) melts and can contribute to fire spread. If the tested system specifies mineral wool, do not substitute PIR — the rating will be invalid.
The role of the stud
The stud is the frame that holds everything together. During a fire test, the stud must:
- Remain in place for the duration of the rating
- Not deform enough to allow boards to fall away
- Transfer loads (for loadbearing walls)
For non-loadbearing partitions, most C studs at 1.2mm gauge survive a fire test — the stud isn't doing much structural work. For loadbearing walls or long-duration tests, heavier gauge may be required.
The critical rule: the stud must match what was tested. If the test used 70mm × 1.2mm C studs, that's what you install. Substituting a larger stud is usually OK (larger is generally better), but substituting a smaller one, a different profile, or a different gauge is not.
Common mistakes
Using the wrong board
If the tested system specifies BG Fireline, using Siniat Fire Board or a generic "fire-rated" board may invalidate the rating. The tested system is the tested system. Match the board brand and type unless the test report explicitly permits substitution.
Missing insulation
As noted above, missing or incomplete insulation is a common cause of fire test failure on site. The insulation must be the correct type, the correct density, and full-fill.
Wrong fixing centres
Board fixing centres are part of the tested system. If the test specified 300mm centres for board fixings, using 600mm centres invalidates the rating. Check the test report.
Poor joint detail
Board joints must be properly staggered (no joints in adjacent layers aligning) and taped/filled per the manufacturer's instructions. Gaps at joints allow fire to penetrate.
Cutting around openings poorly
Openings cut too large, or openings without the correct framing around them, create weak points. Every opening must have doubled studs, a lintel above, and (where required) a sill below.
Missing cavity barriers
For fire-rated walls, cavity barriers are required at certain locations (floor levels, wall junctions, around openings). These are separate from the wall's own fire rating and prevent fire spread through the cavity itself. See our full Cavity Barriers article for details.
Summary
Fire-rated partitions are achieved with tested build-ups, not by adding board layers arbitrarily. Each rating requires a specific combination of board type, thickness, insulation, stud and fixing method. Match the tested system exactly, install it correctly, and use the right cavity barriers where required.
- 30 minutes — 1 layer fire-rated board each side, may not need insulation
- 60 minutes — 1–2 layers of fire-rated board each side, mineral wool insulation
- 90 minutes — 2 layers fire-rated board each side, mineral wool insulation
- 120 minutes — 2–3 layers fire-rated board each side, full-fill mineral wool insulation, wider studs
For any fire-rated system, confirm against the tested report before installation. Our Fire Tested Build-Ups register lists all tested SFS constructions and their fire ratings.
Key Takeaways
- Fire rating is not just about boards — insulation, studs, fixings and joint details all matter
- Always match the tested system — board brand, thickness, layers, insulation, stud and fixing method
- 30 min — 1 layer fire-rated board each side, minimal insulation
- 60 min — 1–2 layers fire-rated board, mineral wool insulation
- 90 min — 2 layers fire-rated board each side, mineral wool insulation
- 120 min — 2–3 layers fire-rated board, full-fill mineral wool, wider studs
- Don't skip cavity barriers — separate requirement from the wall's own rating
- Read the test report — the rating only applies to the tested build-up
Find the right fire-rated build-up for your project
Our Fire Tested Build-Ups register lists every tested SFS construction and its fire rating. Or use our SFS Order Builder to spec the frame.