What is a mezzanine floor?

The meaning in one line

The word comes from the Italian mezzano, meaning “middle”. A mezzanine is a middle floor: a level built partway up a tall room, between the main floor and the ceiling or roof, that is open to the space below on at least one side and usually covers only part of the footprint.

In houses and theatres the word often means a gallery or a balcony. In business premises it nearly always means something more practical: a steel platform put up inside a warehouse, factory, shop or office building to create extra usable floor space without extending the building.

How a commercial mezzanine is built

Most mezzanines in UK commercial buildings are freestanding. They stand on their own steel columns, bolted to the ground floor slab, rather than hanging off the walls or roof of the building. That matters for two reasons: the existing building does not have to carry extra load, and the floor can often be taken down and rebuilt elsewhere if the business moves.

A typical floor has four layers:

• Columns on base plates, fixed into the slab. Each one puts a concentrated load on the floor below, so the slab has to be checked.
• Main beams running between the columns, and secondary beams (often cold-rolled steel sections) spanning between them.
• A deck on top. In dry buildings this is usually structural chipboard; Western Industrial lists 18 mm P5 board for offices and light storage and thicker board, plywood or steel plate for heavier or wet use. Lloyds Beal also installs concrete decks for heavy loads.
• Edge protection: handrails, knee rails and toe boards on open edges, plus staircases, gates and sometimes a goods lift.

Load ratings

Every mezzanine is designed for a stated load, given in kilonewtons per square metre (kN/m²). As a rough guide, Western Industrial lists 3.5 kN/m² for offices and light commercial use, 4.8 kN/m² for general storage and shelving, 6.0 kN/m² for pallet racking and 7.2 kN/m² or more for heavy industrial use. One kN/m² is roughly 100 kg spread over each square metre. The rating should be on the drawings and on a notice by the stairs.

What businesses use mezzanines for

The same structure can serve very different purposes:

• Storage: shelving, archives, spares and slow-moving stock, often the simplest and cheapest kind of floor. See storage mezzanine floors.
• Warehouse operations: picking, packing and returns areas above goods in and dispatch. See warehouse mezzanine floors.
• Offices and welfare: desks, meeting rooms, canteens and changing rooms over a shop floor. See office mezzanine floors.
• Production: assembly, kitting, packing lines and plant platforms. See factory mezzanine floors.
• Retail and leisure: extra sales floor, cafés, gym studios and showroom levels. See retail mezzanine floors.

Is a mezzanine a storey?

For everyday purposes, no: it is an intermediate level inside a storey. For the building regulations, it depends. Approved Document B, the fire safety guidance for England, treats small raised storage floors used by few people and never the public differently from a full floor. Larger floors, or floors where people work, are treated much more like a new storey, with fire-rated construction and escape routes to match. Our guide to mezzanine building regulations goes through the detail.

How much height do you need?

There is no single legal minimum, but a mezzanine only works if people can stand comfortably on both levels. Pallite suggests at least 2.4 metres of working clearance above and below the deck, which points to about 5.5 metres to the underside of the roof as a practical minimum, with 7 metres or more being comfortable. The structure itself takes a few hundred millimetres between the two levels.

Mezzanine or extension?

A mezzanine adds floor area without adding to the building’s footprint, so there is usually no planning application (with exceptions, covered in our planning permission guide), no new foundations beyond the column bases, and no work outside. It is also quicker: the steelwork for many floors goes up in days.

The trade-off is that it only works where there is spare height, and it does not add land, parking or loading bays. If the problem is yard space or dock doors, a mezzanine will not solve it.

What does a mezzanine cost?

Costs depend mainly on size, load and whether the floor needs fire protection. The Mezzanine Company publishes fully installed rates of £300 to £400 per m² for storage and £450 to £600 per m² for offices and retail, while structure-only figures from cost guides are much lower. Our mezzanine floor cost calculator builds a range for your size and use from several published sources.

The short version

A mezzanine floor is a middle level built inside a tall building, usually from a freestanding steel frame and deck. It is designed for a stated load, needs building regulations approval, and may need fire protection depending on its size and use. If you have the height, it is often the cheapest way to add space without moving. When you are ready, our free service can find a mezzanine floor installer who covers your area.