Mezzanine floor fire protection: key facts
- Approved Document B treats a mezzanine as a gallery. In a single storey building, structure that supports a gallery needs fire resistance unless a concession applies.
- The concession in paragraph 7.7 covers storage-only floors with few people, no public, open above and below, and size limits. Offices, production and busy picking floors don't qualify.
- Where the top floor is no more than 5 m above ground, Table B2 gives 60 minutes for storage and industrial buildings without sprinklers and 30 minutes with sprinklers throughout. Offices: 30 minutes either way.
- A floor is tested for fire from the underside. A suspended ceiling only counts towards that if it meets the relevant provisions as a fire-protecting ceiling.
- Fire resistance is classified to BS EN 13501-2. The older BS 476 alternatives are being withdrawn by the 2029 amendments, which take effect on 2 September 2029.
- A new mezzanine is a significant change to the premises. The fire risk assessment must be reviewed and recorded under the Fire Safety Order.
What does fire protection on a mezzanine floor actually do?
It buys time. It keeps the deck, beams and columns standing, and stops flames and heat getting through the floor, for a set number of minutes in a standard test, so people can escape and firefighters can work.
Fire protection doesn't stop a fire. It holds the structure up, and keeps fire below the deck, long enough for the escape plan to work. Approved Document B measures fire resistance in three ways:
| Letter | What it means | Where it matters on a mezzanine |
|---|---|---|
| R | Loadbearing capacity: it doesn't collapse | Columns, main beams, secondary beams |
| E | Integrity: flames and hot gas don't get through | The deck and the ceiling under it |
| I | Insulation: the top surface doesn't get too hot | The deck, so people above can still cross it |
Table B1 sets out which apply. Columns and beams need R, tested on their exposed faces. A floor needs REI, tested with the fire from underneath. That's why the classic protected mezzanine has a fire-rated ceiling below the deck and boards or casings around every column.
The minutes come from a standard test and, in Approved Document B's words, "should not be confused with real time".
When does a mezzanine floor need fire protection?
Assume it does. In a single storey building, Approved Document B says structure supporting a gallery needs fire resistance, unless it's a storage-only raised floor meeting every condition in paragraph 7.7. Offices, production and staffed picking floors normally need protection.
Most structure in a single storey warehouse needs no fire resistance, but paragraph B25(d) makes an exception for anything that supports a gallery. The way out is the raised storage concession in paragraph 7.7, set out in full in our building regulations guide: one tier, storage only, few people and no public, open above and below, compliant escape, and size limits. How that plays out:
| Use of the deck | Can it rely on the storage concession? | Starting assumption |
|---|---|---|
| Bulk or shelved stock, occasional visits | Possibly, if every 7.7 condition is met | Check size against the limits for your detection and sprinkler set-up |
| Order picking with a team working shifts upstairs | Doubtful: "few in number" is hard to argue | Expect fire protection; agree with building control early |
| Offices, canteen, production, packing | No: not storage | Fire-resisting floor and structure |
| Open to the public, or two tiers | No | Fire-resisting floor and structure |
Worked example (ASSUMED figures, for illustration only). A single storey warehouse, no sprinklers, BS 5839-1 detection on the ground floor. Planned: a 24 m by 12 m spare-parts deck, well under half the floor area, visited by two staff a few times a day. Every 7.7 condition is met except size: with detection the limit is 20 m, and this is 24 m. Options: shorten it; agree a larger size with building control and the fire and rescue service (7.7g); fit sprinklers throughout; or fire-protect the structure. Move a picking team up there later and the concession goes, whatever the size.
How many minutes of fire resistance does a mezzanine need?
Approved Document B Table B2 sets it. Where the top floor is no more than 5 m above ground, storage and industrial buildings need 60 minutes without sprinklers and 30 minutes with sprinklers throughout. Offices need 30 minutes either way.
Table B2 works by "purpose group" (the building's main use) and height of the top floor. Single storey buildings use the "up to 5 m" column. The rows most owners meet:
| Purpose group (Table B2) | Without sprinklers | With sprinklers throughout |
|---|---|---|
| Storage and other non-residential (7a) | 60 minutes | 30 minutes |
| Industrial (6) | 60 minutes | 30 minutes |
| Shop and commercial (4) | 60 minutes | 30 minutes |
| Office (3) | 30 minutes | 30 minutes |
Taller buildings have longer periods. "With sprinklers" means the whole building has a system complying with Appendix E. Paragraph B25(a) adds that supporting structure should have no less fire resistance than what it supports, so a 60-minute floor needs 60-minute columns and beams. Ask the designer which row they've used and why, especially for an office or production deck in a storage building.
What's changing in 2029
Approved Document B uses the European classification, BS EN 13501-2, but Table B1 still lists alternatives for products tested to BS 476, marked "effective until 1 September 2029". The 2029 amendments take effect on 2 September 2029 and remove those national classes. Transitional rules cover work notified or applied for earlier that has started, or starts within six months. Either way, ask for BS EN 13501-2 evidence: national ratings "do not automatically equate" with European classes.
What fire protection options are there for a mezzanine?
The usual package is a fire-protecting ceiling under the deck, casings or boards around columns and exposed beams, and a fire-rated fascia at the deck edge. Each one has to be a tested system installed as tested. Detection, sprinklers or compartment walls can change how much of it you need.
| Measure | What it protects | What to check |
|---|---|---|
| Fire-protecting suspended ceiling under the deck | The floor (REI from below) and the secondary beams above it | Tested as a system with this deck type; installed exactly as tested, including access panels and light fittings |
| Column casings or boards | The columns (R) | Full height to the deck structure; impact resistance near truck routes |
| Beam protection at edges and any beam below the ceiling line | Main and edge beams (R) | Every exposed face that the ceiling doesn't cover |
| Fascia or edge panels | The open edge of the deck and the gap between ceiling and edge beam | Fire rating to match the ceiling; how it meets the ceiling |
| Compartment walls or protected enclosures | Separating different uses, or protecting a stair | Continuity at junctions, fire doors, sealed service holes |
Only a fire-protecting ceiling counts. Approved Document B defines one as a ceiling "that adds to the fire resistance of the floor", and says a suspended ceiling should only be relied on if it meets the appropriate provisions. A standard office grid doesn't.
Surfaces count too. The underside of a gallery is a ceiling for lining purposes: Table 6.1 asks for class C-s3, d2 in most rooms and B-s3, d2 in circulation spaces. Ask how the chosen deck (see mezzanine floors) fits the tested ceiling system.
Ask for with every quote: the fire period and the Table B2 row behind it; the tested system for ceiling, columns and beams, with classification report references; and whether ceiling, casings, fascia and fire-stopping are included or excluded. Our mezzanine floor cost calculator lets you add fire protection as its own line.
Can a mezzanine change how your building is compartmented?
Yes. A deck covering more than half the space it sits in counts as a storey, which can make the building multi-storey, with tighter compartment size limits. Other uses may also need separating.
A gallery counts as a storey if its area is more than half that of the space it projects into. That affects more than the deck.
- Compartment sizes. Table 8.1 sets different limits for single and multi-storey buildings. For industrial buildings with a top storey up to 18 m, single storey has no floor area limit; multi-storey is limited to 7,000 m² per storey without sprinklers, or 14,000 m² with them. Beyond the no-sprinkler limits, the table says sprinklers to Appendix E should be provided.
- Different uses. Paragraph 8.3 says parts used mainly for different purposes should be separated by compartment walls or floors, unless one use is ancillary to the other.
- Ancillary upper storeys. Paragraph 8.12 lets a two storey industrial or shop building be treated as single storey for compartmentation if the upper storey is ancillary, no larger than 20% of the ground storey or 500 m² (whichever is lower), compartmented from below and has its own escape route.
Paragraph 8.4 asks for fire resistance to be continuous at joins, with openings that don't reduce it. An open stair or unsealed cable hole breaks a compartment floor. If you're near the half-area line, settle the size with your designer and building control before design.
Does a mezzanine need fire detection or sprinklers?
Not always, but both change what's required. Approved Document B expects automatic detection where a fire in an unattended area could cut off escape, which fits storage under a deck. Detection to BS 5839-1 lifts the storage concession's size limit to 20 m; sprinklers throughout remove it and cut the Table B2 period for storage and industrial buildings from 60 to 30 minutes.
Fire detection and alarm
Paragraph 1.5 says automatic detection and alarm should be provided where a fire could start in an unoccupied part, such as a storage area, and threaten escape from occupied parts: stock burning under a deck while people work above. GOV.UK's factories and warehouses guide agrees that if people on a mezzanine would be unaware of a fire, detection may be needed. Systems should comply with BS 5839-1, with a design, installation and commissioning certificate. Check the alarm can be heard on the deck, and that there's detection under the deck, not just at roof level.
Sprinklers
Sprinklers throughout remove the storage concession's size limit (7.7h), cut the Table B2 period for storage and industrial buildings from 60 to 30 minutes, and can sometimes compensate where a design departs from the guidance (paragraph E4). For non-residential buildings they should be designed and installed to BS EN 12845, with the reliability measures in its Annex F.
How is the escape route from a mezzanine protected?
Escape stairs should normally be protected stairways inside a fire-resisting enclosure, typically REI 30. An open stair is acceptable only where travel distance and people numbers are very limited, such as a storage concession floor. If there's only one way out, keep the numbers and travel distances inside Approved Document B's limits.
Travel distances and stair numbers are in our building regulations guide. This is about protecting those routes.
- Protected stairways. Paragraph 3.23 says every internal escape stair should be a protected stairway, within a fire-resisting enclosure. The exception is an unprotected stair where travel distance and the number of people are very limited; raised storage areas are the example given.
- How much protection. Paragraph 5.2 says that, apart from specific situations, REI 30 is enough to protect means of escape.
- Routes under the deck. If a stair lands under the mezzanine, the protection overhead protects the escape route too.
- Single exits. GOV.UK's factories and warehouses guide says a ground floor and mezzanine served by one exit is generally acceptable if they hold no more than 60 people in total.
Note before design: where stairs land; the walk from each stair foot to a final exit, and whether it passes under the deck; the most people upstairs at once; and the stock stored near the stair.
What will building control ask for on mezzanine fire protection?
A fire strategy that says which route the design takes (the storage concession or fire-resisting structure), the fire period and why, tested evidence for each protection product, details of detection, sprinklers and escape, and proof at the end that it was installed as designed.
A warehouse mezzanine needs a full plans application. On fire, expect your local authority or registered building control approver to want:
- The route. Paragraph 7.7 concession (with each condition shown) or fire-resisting structure.
- The period. The Table B2 row, the top floor height, and whether the building has sprinklers throughout.
- Product evidence. BS EN 13501-2 classification reports for ceiling, column and beam protection; lining classes.
- Junctions. Ceiling to fascia, casing to deck, and fire-stopping around services.
- Detection and sprinklers. BS 5839-1 design and certificate; whole-building sprinkler cover if relied on.
- Escape. Stairs, protected enclosures, travel distances and people numbers.
Varying a 7.7 size limit needs agreement from building control and the fire and rescue service, considering firefighter safety and travel over or under the floor.
Fire safety information at handover. Regulation 38 requires fire safety information to be handed to the responsible person where work includes erecting or extending a building covered by the Fire Safety Order. Whether it formally covers your mezzanine is for building control, but ask for it anyway: it exists so you can understand the fire strategy, maintain the systems and carry out an effective fire risk assessment.
What does a new mezzanine mean for your fire risk assessment?
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person must review the fire risk assessment when the premises undergo significant changes, and record the review. A new mezzanine is that kind of change. Building control checks the design; the assessment covers how the floor is used, stocked and maintained.
Article 9 requires the assessment to be reviewed when premises undergo "significant changes, extensions, or conversions", and article 9(6) requires the review to be recorded as soon as practicable. GOV.UK says you can do it yourself with the official guides or appoint a competent person. The Order applies in England and Wales; Scotland and Northern Ireland have different rules. Two more duties apply once the deck is in use:
- Article 14: routes to emergency exits, and the exits, must be kept clear at all times, and must be adequate for the number of people present. Stock on deck walkways or stair landings breaks this.
- Article 17: fire safety facilities and equipment must be under a suitable system of maintenance and kept in good repair.
Give your fire risk assessor: the approved drawings and fire strategy; any 7.7 conditions relied on; the fire period and products; detection certificates; maximum people upstairs; what's stored on and under the deck; and the completion certificate. Tell your insurer before work starts and ask what they need; only they can say how changes affect cover.
What goes wrong with mezzanine fire protection?
Most failures happen after handover: ceiling tiles lifted and not replaced, holes cut for new cables, casings damaged by trucks, and the use of the deck or the stock beneath it changing without anyone revisiting the fire design.
- Missing ceiling tiles. Lift one for maintenance, swap in a standard tile or leave it out, and the floor above has lost its tested protection.
- Unsealed penetrations. Paragraph 10.1 says every opening for services through a fire-separating element should be fire-stopped. GOV.UK's warehouse guide lists breaches from new cabling as a typical problem.
- Damaged column casings. A dented casing beside a truck route may have opened at the joints. Check casings alongside your racking inspection.
- Use creep. A storage deck gains a packing bench, then desks, then a team. The 7.7 concession assumed storage only and few people.
- Stock below changes. Higher-hazard goods, such as compressed gases or alcoholic liquor, can change the hazard the design assumed; travel distances are shorter for higher-hazard storage.
- Enclosing or extending. Partitions under a concession deck mean it's no longer open above and below. Added bays can break the size limit or the half-area line, and are new building work.
- Racking alterations. Where racking supports the deck, changes to the pallet racking can affect the structure the fire design relied on.
Related guides
Mezzanine floor fire protection: frequently asked questions
Does every mezzanine floor need fire protection?
No. Approved Document B lets a storage-only raised floor go without fire-resisting structure if it meets every condition in paragraph 7.7: one tier, few people and no public, open above and below, compliant escape and size limits. Most other mezzanines in single storey buildings need fire-resisting structure.
How long does mezzanine fire protection need to last?
Approved Document B Table B2 sets the minimum. Where the top floor is no more than 5 m above ground, storage and industrial buildings need 60 minutes without sprinklers and 30 minutes with sprinklers throughout. Offices need 30 minutes. The minutes refer to a standard test, not real time.
Why does a mezzanine need a fire-rated ceiling?
Approved Document B tests a floor's fire resistance from the underside. A fire-protecting suspended ceiling adds to the floor's fire resistance, but only if it meets the relevant provisions as a tested system. A standard ceiling grid doesn't count.
Do sprinklers mean I don't need mezzanine fire protection?
Not automatically. Sprinklers throughout remove the size limit on a storage-only concession floor and cut the Table B2 period for storage and industrial buildings from 60 to 30 minutes. Other mezzanines still need protection.
Can we pick orders on a storage mezzanine without fire protection?
Only if every paragraph 7.7 condition is still met, including storage purposes only and few people on the floor. A regular picking team is hard to fit within that. Ask building control before changing how the deck is used.
Does a mezzanine need fire detection?
Approved Document B expects automatic detection where a fire in an unoccupied area, such as storage, could threaten escape from occupied parts. Detection to BS 5839-1 on the lower level also lets a storage concession floor be up to 20 m in width or length.
What happens to BS 476 fire ratings in 2029?
The 2029 amendments to Approved Document B take effect in England on 2 September 2029 and remove the national classes for fire resistance. Products should have evidence classified to BS EN 13501-2. Transitional rules cover work already notified or applied for.
Do I need a new fire risk assessment after installing a mezzanine?
You must review it. The Regulatory Reform (Fire Safety) Order 2005 requires a review, recorded, when premises undergo significant changes, and a new mezzanine is one.
Can we run new cables through a fire-rated mezzanine ceiling?
Only if the openings are fire-stopped afterwards. Approved Document B says every opening for services through a fire-separating element should be sealed with fire-stopping. Use a competent contractor and a tested product, and record the work.
Sources
We checked the facts on this page against these sources on 13 November 2026:
- Fire safety: Approved Document B (GOV.UK)
- Regulatory Reform (Fire Safety) Order 2005, article 9 (risk assessment)
- Regulatory Reform (Fire Safety) Order 2005, article 14 (emergency routes and exits)
- Regulatory Reform (Fire Safety) Order 2005, article 17 (maintenance)
- Fire safety in the workplace: fire risk assessments (GOV.UK)
- Fire safety risk assessment: factories and warehouses (GOV.UK)