Why does a mezzanine floor affect fire safety?
A mezzanine floor physically changes the building. It introduces a new level, alters how fire and smoke can travel through the internal volume, changes travel distances to escape routes, and creates a structure that – unless protected – can fail in a fire and compromise the safety of occupants above and below.
Building regulations treat a mezzanine as a permanent structural alteration to the building, not as furniture or equipment. The building’s fire strategy – the set of measures that together provide adequate means of escape, fire detection and structural fire resistance – must be reassessed to account for the mezzanine. That reassessment is carried out as part of the building regulations approval process.
Which regulations and approved documents apply?
Fire safety for mezzanine floors is governed by the Building Regulations 2010 and principally Approved Document B (Fire Safety). Approved Document B sets out requirements for:
- Means of warning and escape – fire detection, alarm and escape route provision
- Internal fire spread through the structure – fire resistance of floors, walls and structural elements
- External fire spread – less relevant for internal mezzanines but applicable where external works are involved
- Access and facilities for the fire service
The Regulatory Reform (Fire Safety) Order 2005 also applies to most commercial and industrial buildings and requires the responsible person to carry out a fire risk assessment. Installing a mezzanine changes the building and therefore requires the fire risk assessment to be reviewed and updated. This is a separate obligation from building regulations approval, though the two processes inform each other.
How does occupancy type determine fire safety requirements?
Intended use is the single most important factor in determining fire safety requirements for a mezzanine. The same structure can attract significantly different requirements depending on what it is used for.
- Storage only, infrequently accessed: the lowest level of fire safety requirement. Means of escape provisions are less onerous where occupancy is low and intermittent. Fire protection to steelwork may not be required depending on the fire strategy.
- General industrial or production use: moderate requirements. Escape routes and travel distances must be assessed. Fire protection to steelwork is commonly required.
- Office accommodation: more demanding requirements. A fire-rated ceiling beneath the mezzanine deck is typically required to provide compartmentation between the office level and the space below. Fire protection to steelwork, compliant escape routes and fire detection provisions are standard.
- Retail or public access: the most demanding category. Members of the public are assumed to be less familiar with the building and escape routes. Additional provisions for signage, emergency lighting, escape route width and fire suppression commonly apply.
These distinctions are not optional interpretations – they reflect the occupancy classifications in Approved Document B and are applied by building control in assessing compliance.
When is fire protection to steelwork required?
Fire protection to the supporting steelwork of a mezzanine is required where the structure needs to maintain its load-bearing capacity for a defined period in the event of a fire. The required fire resistance period – commonly 30 or 60 minutes – is determined by the fire strategy for the building, which takes into account occupancy, building size, escape provisions and whether sprinklers are present.
Protection is achieved by one of three principal methods:
- Intumescent coatings: paint-like coatings applied to the steel that expand when exposed to heat, forming an insulating char layer. The most common method for mezzanine steelwork.
- Board encasement: fire-resistant board fixed around the structural member. Used where a higher fire resistance period is required or where surface finish is important.
- Sprayed protection: mineral fibre or cementitious material applied to the steel surface. Less common in occupied mezzanine environments.
Where the fire strategy determines that fire protection to steelwork is required, it is mandatory – not a cost option. Unprotected steelwork that does not meet the required fire resistance period will not achieve building regulations compliance.
One of the most common questions when planning a mezzanine floor is whether the structural steelwork needs to be fireproofed.
The answer depends on the fire strategy for your building. Where the steelwork needs to maintain its load-bearing capacity for a defined period in a fire, protection is required. The fire resistance period is commonly 30 or 60 minutes, and is determined by occupancy type, building size, escape provisions and whether sprinklers are present.
There are three main methods. Intumescent coatings – a paint-like coating that expands under heat to form an insulating layer – are the most common approach for mezzanine steelwork. Board encasement fixes fire-resistant board around the structural member, and is used where a higher resistance period is needed or where surface finish matters. Sprayed mineral fibre is a third option, though less common in occupied environments.
The important point is this: where fire protection to steelwork is required, it is mandatory. It is not a cost option that can be removed at value engineering stage.
The full reference guide covers how occupancy, escape routes and sprinkler coverage all feed into the fire strategy for a mezzanine – and what that means for compliance.
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When is fire protection required to mezzanine floor steelwork?
Fire protection to mezzanine steelwork is one of the most frequently asked questions in the design and compliance process – and the answer isn’t always straightforward.
This short guide explains when fire protection to steelwork is required, how the fire resistance period (commonly thirty or sixty minutes) is determined, and what the three main protection methods are: intumescent coatings, board encasement and sprayed mineral fibre.
It also covers a point that often surprises people at value engineering stage: where protection is required, it is mandatory – not optional.
What fire-rated construction is required to the floor deck?
Where a mezzanine creates a floor between two occupied or potentially occupied levels, fire-rated construction to the underside of the deck is required to provide compartmentation – limiting the spread of fire and smoke between levels.
For office mezzanines, a fire-rated suspended ceiling beneath the deck is the standard solution. The ceiling provides the required fire resistance period and also conceals services and improves the finished appearance of the space. The deck material itself – typically particleboard – contributes to the overall fire resistance of the assembly when combined with the ceiling below.
For storage mezzanines where the underside of the deck is exposed, the fire strategy may determine that a rated ceiling is not required, depending on the occupancy, building size and escape provisions. This is confirmed through building control assessment, not assumed.
How does a mezzanine affect means of escape?
A mezzanine introduces a new level from which occupants must be able to escape. Means of escape provisions must ensure that anyone on the mezzanine can reach a place of safety within an acceptable travel distance, without passing through areas of high fire risk.
The key factors building control will assess are:
- Travel distance from the furthest point on the mezzanine to a protected escape route or final exit, measured in accordance with Approved Document B limits for the occupancy type
- Number of escape routes – where travel distance or occupancy exceeds defined thresholds, more than one escape stair may be required
- Stair geometry – stair rise, going, width and handrail provision must comply with Approved Document K
- Emergency lighting and exit signage on the mezzanine level
A mezzanine that pushes escape travel distances beyond compliant limits, or that creates a dead-end condition from which there is only one direction of escape, will require a second stair or a redesign of the floor layout.
When do sprinklers need to be modified?
Where a building already has a sprinkler system, installing a mezzanine floor will almost always require modifications to the system. The mezzanine deck obstructs the coverage pattern of sprinkler heads above it, leaving the area beneath the deck unprotected. Additional sprinkler heads must be installed beneath the mezzanine to restore coverage.
Where a mezzanine pushes the building’s total floor area or occupied area past thresholds that trigger a sprinkler requirement under building regulations or insurance conditions, a new sprinkler system may need to be installed across the building, not just beneath the mezzanine. This is a significant cost consideration and should be assessed at feasibility stage, not after design has been fixed.
