Office mezzanine floors: what changes when people work up there all day

What changes when a mezzanine is used for offices instead of storage?

Almost everything except the steel. An office mezzanine holds more people, needs fire-resisting structure and proper escape, has to meet workplace standards for temperature, ventilation, lighting and space, needs toilets and rest facilities nearby, and must give reasonable access to disabled people.

A storage mezzanine is visited. An office mezzanine is occupied, and many of the easier routes open to a storage floor close once desks go up there.

If you're still deciding whether any mezzanine suits your building (height, columns, the slab), start with our guide to mezzanine floors. This page assumes you want offices up there.

What does the floor need to carry when it holds offices?

More than desks and people. The design must include partitions, ceilings, glazing, toilets, kitchens, services and furniture. Get the design load in writing for each area of the deck, and have it marked on the floor.

Office and storage uses are designed for different loads, and the designer picks figures for the use you describe. We don't quote kN/m² values: they're in paid structural standards and depend on your layout. What you control is the brief. Tell the designer about:

• partitions, doors and glazed screens, and whether you might move them later
• the suspended ceiling, lights, ductwork and heaters hung from it or from the deck
• toilets, washbasins and a kitchen, with water and drainage
• filing, safes, comms cabinets and printers: heavy items on small footprints
• the number of people at the busiest time, including meetings and training

HSE's warehouse guidance (HSG76) says mezzanine floors should be clearly marked with their safe load-bearing capacity and any restrictions on use. On a mixed deck that means separate figures for office and storage areas.

Converting a storage mezzanine? The structure, fire protection and escape were designed for storage. Get it checked by a competent structural engineer before you buy furniture, and treat it as building work that needs approval.

How are mezzanine offices partitioned, ceilinged and glazed?

Partitions are fixed to the deck, a suspended ceiling closes the space above, and the ceiling under the deck often has to be fire-resisting. Glazing overlooking the warehouse must be safety material, or protected, wherever that's needed for health or safety.

• Walls. Partitions sit on and are tied to the deck. Ask whether any are fire-resisting, form part of an escape route or protect a stair.
• The ceiling above. A suspended ceiling carries lights, holds heat and cuts noise. Under a high warehouse roof it also decides how much air you heat.
• The ceiling below. Approved Document B says elements of structure supporting a gallery need fire resistance, even in a single storey building. That's why office mezzanines usually have a fire-resisting ceiling under the deck and column casings.

Glazing to the warehouse

Regulation 14 of the Workplace (Health, Safety and Welfare) Regulations 1992 says transparent surfaces in walls, partitions and doors must, where necessary for health or safety, be of safety material or protected against breakage, and be marked or designed so they're obvious. HSE's Approved Code of Practice (L24) says to pay particular attention to glazing at waist level or below in walls and partitions, and at shoulder level or below in doors. Ask whether the screen is also part of the fire strategy.

Noise and dust from below

No regulation sets a noise level for an office over a warehouse, but it's a common complaint. Deal with it at design stage: keep offices away from docks and noisy lines, seal partition heads and service holes, use a self-closing door at the top of the stair, and ask what glazing specification the supplier offers for sound.

What temperature, ventilation, lighting and space does a mezzanine office need?

The Workplace Regulations require a reasonable temperature, enough fresh air, suitable lighting (natural where reasonably practicable) and enough space. HSE's Approved Code of Practice gives a normal minimum of 16°C and at least 11 m³ per person.

The Workplace Regulations apply in England, Wales and Scotland, and HSE's L24 explains how to meet them. A warehouse can be cold, draughty, dim and very high: the office has to fix all four.

Worked example (ASSUMED figures)

These numbers are invented to show the method, not a typical size.

• Assumed office: 8 m x 6 m = 48 m², ceiling at 2.6 m.
• Space (L24): 48 x 2.6 = 124.8 m³, ÷ 11 = about 11 people before furniture. Desks and walkways bring the practical number down.
• Escape design (ADB Table D1): if headcount isn't known, 48 ÷ 6 = 8 people. Planning for more? Give the designer the real number.
• Fresh air (Approved Document F, offices): the higher of 10 l/s per person (8 people = 80 l/s) or 1 l/s per m² (48 l/s), so 80 l/s.

Run these before you ask for quotes. If headcount, space and fresh air don't agree, it's cheaper to find out now.

Do heating, lighting and ventilation in a mezzanine office bring in Parts L and F?

Often, yes. Heating a space that wasn't heated before can be a change to energy status, which brings in Part L. Part F ventilation doesn't apply to space used solely for storage, but it does apply to offices.

Part L: energy. The Building Regulations 2010 define a change to a building's energy status as any change that makes the energy efficiency requirements apply where they previously didn't. Regulation 22 then requires whatever work is needed for the building to comply with Part L. Approved Document L Volume 2 gives the example of a previously unheated space becoming part of the heated building. A heated office inside an unheated warehouse is the case to raise with building control early: it can affect insulation of the office walls and ceiling, and the standard of the heating, lighting and mechanical ventilation (the regulations' "fixed building services").

Part F: ventilation. Requirement F1 says there must be adequate means of ventilation for people in the building, but it doesn't apply to space "used solely for storage". For offices, Approved Document F Volume 2 (2021 edition) gives:

• outdoor air at 10 l/s per person or 1 l/s per m², whichever gives the higher total
• extract ventilation in toilets, washrooms and food and drink preparation areas
• a means of purge ventilation for each office, and controls to adjust each room

Your mezzanine supplier may not design heating, ventilation and lighting. Find out who does, and make sure those drawings go in with the building regulations application.

Do you need toilets, drinking water and a rest area for mezzanine office staff?

You must provide suitable and sufficient toilets, washing facilities, drinking water and rest facilities at readily accessible places. HSE's Approved Code of Practice sets minimum numbers of toilets and washbasins by the number of people at work at any one time.

Regulations 20 to 25 of the Workplace Regulations cover welfare for the whole workforce, so an office team can tip existing facilities over the limit.

Source: HSE L24, Table 1 (men and women working). If separate toilets serve a group, such as office workers and manual workers, L24 says calculate each group separately.

• Location. L24 says facilities don't have to be within the workplace but should, if possible, be within the building, so ground-floor toilets can serve the mezzanine.
• Accessible toilet. Approved Document M asks for at least one wheelchair-accessible unisex toilet at each location where toilets are provided for people working in the building.
• Drinking water (reg 22): wholesome, readily accessible, with cups unless it's a drinking jet.
• Rest and meals (reg 25): suitable rest facilities, and somewhere to eat where meals are regularly eaten at work. In offices, L24 says seats in the work area can be enough if people aren't disturbed during breaks.

Does an office mezzanine need a lift for disabled access?

Approved Document M calls a passenger lift the most suitable way between storeys. In an existing building a lifting platform is acceptable where a lift can't reasonably be accommodated. There's no size or headcount below which access can be ignored, so agree the approach with building control before work starts.

There's no simple threshold. Here's what Approved Document M Volume 2 (England) says:

• It applies. Part M applies when an existing non-domestic building undergoes a material alteration. Altered arrangements for getting between levels must comply with Requirement M1, and the building must be no less compliant afterwards.
• A lift is preferred. Paragraph 3.21: a passenger lift is the most suitable form of access between storeys.
• Existing buildings have alternatives. Paragraph 3.24: a passenger lift or, if one can't reasonably be accommodated, a lifting platform designed for the height; a wheelchair platform stairlift serving an intermediate level only in exceptional circumstances.
• Stairs still matter. Paragraph 3.19: internal stairs should always be provided as well, designed for ambulant disabled people and people with impaired sight.
• Agree it early. Paragraphs 0.21 to 0.24: if you propose a different solution, it's for you to show it works, and the level of provision should be agreed with the building control body before work starts and recorded.

Approval isn't the end of it. Approved Document M notes that building control approval doesn't necessarily mean you've met your Equality Act 2010 duties, and Workplace Regulation 25A requires the parts of a workplace used by disabled workers (stairs, doors, toilets, workstations) to take account of them.

How do people escape from an office mezzanine in a fire?

The deck needs early warning of fire and a safe route out. Approved Document B limits office travel distance to 18 m where escape is in one direction only and 45 m where there's more than one, and the office use rules out the storage-only fire concession.

The detail is in our guide to mezzanine floor building regulations. What's different about offices:

• Tighter one-way distance: 18 m for offices against 25 m for normal hazard storage (ADB Table 2.1). A long deck with one stair at the end can fail this.
• More people: 6 m² per person instead of 30 means five times the occupants for the same area. Table 2.2 sets a minimum of one escape route for up to 60 people, but travel distances often call for a second stair well before that.
• No storage concession: paragraph 7.7 is for storage only, so expect a protected ceiling under the deck and column casings.
• A separate use? ADB assigns an ancillary use its own purpose group where the building is over 280 m² and that use is more than one-fifth of the floor area.
• Warning: ask how the fire alarm will be heard inside a closed office.

Under article 9 of the Regulatory Reform (Fire Safety) Order 2005, review your fire risk assessment when the premises undergo significant changes.

Does an office mezzanine need planning permission?

Often not, because works affecting only the interior generally aren't development. But listed buildings, planning conditions, external changes and some uses can still bring planning in, so check with your local planning authority.

Section 55 of the Town and Country Planning Act 1990 says works affecting only the interior of a building, or not materially affecting its external appearance, generally aren't development. In England the main exception is retail: internal works adding more than 200 m² of floor space in a building used for retail sale of goods (other than hot food) count as development. For an office, also check new windows, plant or flues outside, conditions on your existing permission and listed status. GOV.UK says you might need building regulations approval and planning permission. If you lease, landlord consent is a separate question.

What should you decide and ask before getting office mezzanine quotes?

Decide headcount, rooms and services first, then ask every supplier the same questions. A quote that leaves out fire protection, heating and ventilation or access isn't comparable with one that includes them.

1. Headcount: normal and peak, including visitors and meetings.
2. Rooms: open plan, private offices, meeting room, kitchen, toilets.
3. Position: away from noise, near drainage and power, with escape in mind.
4. Height: headroom under the deck and inside the office once the ceiling is in.
5. Access: who must get upstairs, and what could stay downstairs.

Ask every supplier

• What design load have you used for the office area, including partitions and ceilings?
• Is fire protection included: ceiling below, column casings, fire-resisting partitions and glazing?
• How many stairs, and what's the travel distance from the furthest desk?
• What access arrangement have you assumed, and has building control agreed it?
• Who designs heating, ventilation and lighting to Parts L and F, and is it priced?
• Who applies for building regulations approval, and what do I get at handover?

To put rough numbers on the floor itself, use our mezzanine floor cost calculator with your own rates, and add the fit-out and services as separate lines.

Related guides

Office mezzanine floors: frequently asked questions

Sources

We checked the facts on this page against these sources on 13 November 2026:

• HSE: Workplace health, safety and welfare (L24, Approved Code of Practice)
• The Workplace (Health, Safety and Welfare) Regulations 1992 (legislation.gov.uk)
• GOV.UK: Access to and use of buildings, Approved Document M
• GOV.UK: Fire safety, Approved Document B
• GOV.UK: Ventilation, Approved Document F
• GOV.UK: Conservation of fuel and power, Approved Document L
• The Building Regulations 2010, regulation 22 (legislation.gov.uk)

This guide is general information for UK businesses, not legal, structural engineering, building control, fire safety or health and safety advice. Warehouse Racking Hub is an independent guide. We don't design, supply, install or inspect racking or mezzanine floors ourselves. If you ask us to, we'll put you in touch with one storage systems specialist from our partners that covers your area.

Back to the top ↑