What building regulations apply to a mezzanine floor?

Why a mezzanine needs approval

A mezzanine is building work. It adds a structure that people stand on, puts new loads on the ground slab and changes how anyone upstairs escapes in a fire. So, even when no planning permission is needed, the work needs approval under the Building Regulations before it starts and a completion certificate when it is finished.

In England and Wales you can use the council’s building control service or a registered building control approver. Most mezzanine installers prepare the drawings and calculations and make the application for you, and some include the cost in their price. Scotland uses a building warrant system instead.

The regulations themselves are short. The detail sits in the Approved Documents, which describe ways to comply. Three of them matter most for a mezzanine.

Part A: structure

Building control needs to see that the floor will safely carry its own weight and the loads put on it. That means structural calculations showing:

• the design imposed load, usually in kN/m², and any point loads
• how the frame stays stable sideways, through bracing or fixing
• the loads at each column base and what the slab must carry
• the deck type and thickness

For storage mezzanines in warehouse-type buildings, designers can use BRE Digest 437, a guide for industrial platform floors. Jersey’s building control guidance explains that it allows design for lower imposed loads than the general code, provided there is a management document for the floor and loading notices by the stairs and loading points. Whatever method is used, the design load should appear on the drawings and on a notice on the floor.

Part B: fire safety and escape

This is where most of the cost and argument lies.

When a floor needs fire protection

Approved Document B, Volume 2 (paragraphs 7.6 and 7.7) treats small raised storage floors differently from full floors. Industry guidance reads the conditions broadly as follows:

• used only for storage, by a small number of staff and never the public
• a single tier, open above and below to the space it sits in
• within size limits; Western Industrial gives under 20 metres in every direction and no more than half the floor area of the room

Rapid Racking, writing in Logistics Matters, sums up the practice: floors over 10 metres in any direction need smoke detection underneath, and floors over 20 metres need fire protection, meaning a fire-rated ceiling under the deck, a perimeter fascia and casings on the columns, unless the building is sprinklered.

Once a floor is used for offices, production, packing or retail, or is open to the public, it is generally treated as a floor that needs fire resistance. Western Industrial gives 60 minutes as the usual specification, with 30 minutes the minimum where the upper floor is no more than 5 metres above ground, and says fire protection adds roughly 15 to 30% to the cost of the structure.

Escape distances

Approved Document B limits how far anyone has to travel to reach a way out. Table 2.1 gives:

On a large floor, these limits often decide whether a second staircase is needed. Our mezzanine floor design page explains how stair positions are chosen.

Part K: stairs and guarding

Approved Document K covers stairs, handrails and edge protection:

• Utility stairs (staff only): rise 150 to 190 mm, going 250 to 400 mm, up to 16 risers per flight.
• General access stairs (where the public go): rise 150 to 170 mm, going 250 to 400 mm, usually up to 12 risers.
• Twice the rise plus the going should be between 550 and 700 mm.
• Handrails 900 to 1000 mm above the pitch line; headroom of at least 2 metres on escape routes.
• Guarding at the edges of floors and landings in factories and warehouses: 1100 mm; on stairs, 900 mm.

For industrial buildings, Part K also points to BS 5395-3 for industrial stairs, ladders and walkways. Our mezzanine stairs guide covers this in more depth.

Other rules that apply

• Access for disabled people (Part M) matters for floors open to the public or used as offices; a lift may be needed.
• Workplace regulations still apply once the floor is in use: safe access, lighting and floors fit for their loads.
• Structural steel is made to BS EN 1090 with UKCA or CE marking, as Pallite notes; ask the installer for the declaration.

What you should receive at the end

• approved drawings and structural calculations
• a completion certificate from building control
• a loading notice to display at the stairs
• details of the fire protection fitted and any detection extended under the floor

Keep these with your fire risk assessment. Insurers, landlords and future buyers will ask for them.

How this affects price

Fire protection, extra stairs and detection can add thousands of pounds to a floor, so the use you choose matters. Our mezzanine floor cost calculator shows the difference between a storage floor and an office floor of the same size.

This guide is general information, not professional advice. Your building control body has the final say, and a good mezzanine floor installer will design to the rules from the first drawing.