Mezzanine floors: when installation needs permission

Installing a mezzanine inside an existing building usually needs no planning permission, because section 55(2)(a) of the Town and Country Planning Act 1990 says works affecting only the interior of a building are not development. There is one specific exception and one general one. The specific exception is retail: under section 55(2A), inserting a mezzanine floor into a building used for retail purposes is development where the mezzanine exceeds 200 square metres of gross internal area. The general exception is that any mezzanine, in any building, needs permission if it results in a material change of use.

Building regulations approval is required either way, and that is not optional.

When internal works become development

Start with the two tests, in order.

Does section 55(2A) apply? That means asking whether the building is used for retail purposes and whether the proposed mezzanine, taken as a whole, exceeds 200 square metres gross internal area. If both are yes, the works are building operations and a planning application is needed.

Does the mezzanine change the use? A mezzanine used for additional storage in a warehouse changes nothing. A mezzanine that converts part of a Class B8 warehouse into a trade showroom open to the public may well amount to a material change of use, and that is development regardless of floor area. The same logic applies to a mezzanine in a gym used for a nursery, or in an industrial unit used for offices beyond an ancillary level.

Two practical points that catch people out. The 200 square metre figure applies to the mezzanine, not to the building, and a scheme phased into two 150 square metre mezzanines in the same unit invites the council to look at the total. And the retail provision refers to buildings used for retail purposes, which is a question about actual use rather than about the letter of the use class.

The retail mezzanine provision

The provision was inserted by the Planning and Compulsory Purchase Act 2004 for a policy reason: large retail warehouses were adding substantial sales floorspace internally, with no application and therefore no assessment of the effect on town centres or on the highway network.

That policy background tells you what the application will be about. The council will not be interested in the steelwork. It will be interested in three things.

• Whether the additional floorspace is sales area or ancillary storage, staff or plant space.
• What the additional sales area does to the vitality and viability of nearby centres.
• What it does to trip generation and parking demand.

Answer those directly in the Planning Statement and the application becomes straightforward. Leave them to be inferred from a floor plan and it will not.

Note also that additional gross internal area created by a mezzanine can attract a Community Infrastructure Levy charge where the authority has a charging schedule covering retail. Check the schedule before you budget, because the levy is calculated on the net additional floorspace and is payable on commencement.

Transport and parking implications

Extra floorspace means extra trips, at least in the council's model.

For a modest mezzanine the highway authority will normally accept a Transport Statement that sets out the existing parking provision, the existing and proposed floorspace by use, trip generation from a recognised database, and an assessment of whether the current car park can absorb the change. Where the parking survey shows spare capacity at peak, the point is usually resolved.

The argument gets harder where the store already overspills at weekends, or where the additional area is sales rather than storage. Sales floorspace generates far more customer trips per square metre than storage does, so the split you declare on the drawings has consequences beyond retail policy.

Servicing is worth addressing too. A mezzanine adds stock, which adds deliveries, and a service yard designed for two deliveries a day may not take four.

Retail impact where the extra space is sales area

National policy requires a retail impact assessment for main town centre uses outside a defined centre where the proposal exceeds a floorspace threshold, which is set locally where the plan specifies one and otherwise falls back to the national default. That means a mezzanine in an out-of-centre retail warehouse can trigger a Retail Impact Assessment even though the building footprint is unchanged.

The assessment looks at the effect on existing, committed and planned public and private investment in nearby centres, and at the effect on town centre vitality and viability. A sequential test may also apply, asking whether the floorspace could be accommodated in a centre first.

Where the mezzanine is only for storage, say so and accept a condition restricting its use. A condition limiting the mezzanine to ancillary storage, with no display or sales to the public, is a common and workable outcome, and it is much easier to accept at the outset than to argue about later.

Fire safety and building regulations

A mezzanine changes the fire strategy of a building, and this is where the real technical work sits.

Approved Document B covers means of escape, travel distances from the mezzanine to a protected route, the number and width of escape stairs, compartmentation and the fire resistance of the mezzanine structure. Open mezzanines in single-storey buildings are treated differently from enclosed ones, and area limits apply. Sprinkler provision under the relevant standard is sometimes the route to a workable design where travel distances are otherwise exceeded.

Structural design under the Eurocodes, loading assumptions for storage versus retail, and accessibility under Approved Document M all follow. Where the building is occupied, the Regulatory Reform (Fire Safety) Order 2005 duties on the responsible person apply throughout the works and afterwards, and the fire risk assessment has to be revised.

None of that is a planning matter. All of it can stop the project, so involve the building control body and a fire engineer before the layout is fixed.

Evidence to submit

For a mezzanine application caught by section 55(2A), a workable pack looks like this.

1. Existing and proposed floor plans, sections and elevations, with the mezzanine area figured on the drawing.
2. A floorspace schedule showing existing and proposed gross internal area, split between sales, storage, staff and plant.
3. A planning statement addressing the 200 square metre trigger, the use of the additional space and the relevant retail policy.
4. A transport statement with parking accumulation data where the additional area is sales.
5. A retail impact assessment where the local or national threshold is exceeded.
6. Confirmation of the position on the Community Infrastructure Levy, with the additional information form.

Enforcement risk of installing first

Building a mezzanine that needed permission, without it, is a breach of planning control. The council can serve an enforcement notice requiring removal, and appealing on ground (a), that permission ought to be granted, puts you in the same policy argument from a much weaker position.

Time limits for taking enforcement action against operational development were changed by the Levelling-up and Regeneration Act 2023, extending the period for breaches occurring after the relevant commencement date. Check the current position rather than relying on the old four-year rule, because the answer now depends on when the breach occurred.

And there is a commercial risk that has nothing to do with the council. An unauthorised mezzanine appears in every purchaser's and every lender's due diligence, and it is the sort of item that reduces a price or delays a completion until it is regularised.

Browse the 66 PlanScope report types to see which documents a floorspace application usually needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval, and this is general guidance rather than legal advice.