Mixed-use buildings, housing above shops: fire, accessibility and planning 2026

A mixed-use building combines the regulation of residential buildings — the order of 31 January 1986 as amended, classified in families 1 to 4 — with the public-building regulation of 25 June 1980 for the retail part. The two bodies of rules were not designed to articulate with each other: it is practice, the building research centre's guidance and the safety commissions' opinions that define how they coexist.

The basic rule is physical separation between the residential part and the public part by a fire-resisting construction. That construction must be REI 120 where it separates a building open to the public in the first four categories from housing. For a fifth-category establishment the requirement can fall to REI 60 according to the risk analysis. It includes the separating floors above the ground-floor unit and the lateral walls.

Any penetration of the fire separation by a service — electricity, plumbing, ventilation, ductwork — must be protected by a fire damper, an intumescent sleeve or an appropriate collar. This is a frequent point of vigilance during construction: untreated penetrations cancel the fire resistance of the wall. The fire safety coordinator must ensure that every actuator crossing the separation is connected to the detection system.

The question of circulation is crucial. Two regulatory options exist.

Option one, strictly separated circulation: a separate entrance for the public part and for the dwellings, separate lifts, separate stairs. This is the simplest solution in regulatory terms, but it penalises the usable area and raises the cost of the common parts.

Option two, shared circulation: residents may reach the upper floors through a hall shared with the public part, subject to specific separation. The shared entrance hall is then treated as a public space — escape widths, emergency lighting, smoke control. That solution is cheaper but requires precise analysis by the safety commission.

ℹ Point of vigilance: the shared stair If a single stair serves both the residential floors and the ground-floor public unit, it must satisfy the more demanding requirements of both regimes. In practice: at least one unit of passage, 0.90 m clear, on the public side; EI 60 or EI 30 enclosure according to the category; smoke control under both regulations. The safety commission may impose an enclosed stair dedicated to the public part, independent of the residential stairs.

Where a building houses several regulated activities, the more demanding regulation applies to the shared structure. The general principle is that the residential part follows the 1986 order and the public part follows the public-building regulation. The shared structural requirements — load-bearing floors, stairs — must satisfy both simultaneously, which means adopting the higher requirement.

Covered parking within a mixed-use building falls under the car park regime. Basements must be subdivided into compartments below 3,000 m² separated by REI 60 walls, with carbon monoxide detectors triggering the ventilation, and smoke control at six air changes an hour or 900 m³/h per vehicle. Separation between the car park and the residential part is REI 120, as is separation between the car park and the public part.

Dwellings on upper floors must meet the accessibility standards for new residential buildings: every dwelling at ground floor or served by a lift must be accessible or adaptable. The common circulation — corridors, landings, lift — must comply with the width and manoeuvring standards.

The ground-floor retail unit must meet the accessibility standards for buildings open to the public: level entry, an accessible internal route, accessible sanitary accommodation where the establishment provides any, an accessible till. The two regimes do not share the same requirements on escape width or counter height: the architect must treat them separately zone by zone.

Where one lift serves both the dwellings and the public part, through a shared hall, its characteristics must satisfy both regulations. The minimum car size is that required for buildings open to the public — 1.00 m × 1.40 m with a 0.90 m door — which is generally more demanding than for dwellings alone.

The local plan distinguishes permitted uses by zone. A city-centre urban zone may allow both retail and housing, but with different rules by use: massing, site coverage, parking. Economist and architect must ensure the areas allocated to each use respect the local coefficients and ratios, notably the parking spaces required, which differ between shops and dwellings.

As a general rule a mixed-use building is the subject of a single planning application, even where the uses are multiple. The application must include a safety statement specific to the retail part and an accessibility certificate for the whole building. A later change in the retail activity — a new tenant, a change of trade altering the regulatory type — may require a fresh application or a prior declaration.

Floor area is calculated for the whole building. The regulatory deductions — parking, plant rooms, external insulation thickness — are the same for every use. The split between residential and retail floor area matters for the land appraisal of the operation.

The environmental regulations apply by use: the residential part follows the apartment thresholds, the retail part follows the commercial thresholds. Where the two parts share the same thermal installation — a central heat pump, a district connection — the assessments must be separated in the regulatory calculation. The compliance certificate is produced by use.

ℹ A frequent case: unheated shops below heated dwellings If the ground-floor retail unit is unheated, delivered as a bare shell, it falls outside the environmental regulations for the retail part. Note, however, that the thermal bridges between the unheated ground floor and the floors of the flats above must be modelled in the dwellings' bioclimatic calculation. A common solution is a first-floor slab with reinforced insulation to break the thermal link with the retail unit.

The regulatory complexity of a mixed-use building generates direct and indirect premiums. The direct ones correspond to the additional construction — fire walls, dual-regime fire safety cabling. The indirect ones arise from the reinforced coordination between trades and from more complex regulatory monitoring.

ℹ ✔ Summary for the economist Anticipate the position of the REI 120 separation from the concept stage: it structures the project. Allow for two distinct regulatory files: housing, by the design team, and the public part, by the technical control office. Typical budget for a mixed operation of one to four upper floors with ground-floor retail: 1,730 – 2,450 €/m² of floor area overall. Estimated regulatory premium: + 5 to 15 % against a single-use operation of the same massing. Check the local plan: some zones require active ground floors with an obligation to maintain retail for a set number of years. Allow for the safety commission visit and opinion before the shop opens.

Fire regulation of apartment buildings is detailed in the residential block article. Public-building obligations for shops are treated in the retail article. The fire safety article covers the principles of resistance and reaction to fire applicable to both regimes. For local plan rules and floor area calculation, see the planning article.

ℹ The construction economist on demand. A mixed-use building means two regulations and one operation. Quostra prices the residential and public packages separately, builds in the fire separation premiums and produces an overall estimate from the sketch stage.

Reference basis of the figures

The ratios per square metre and per item on this page are stated in January 2026 values. They were updated from January 2025 values, the basis adopted for the whole cocoon, using the BT01 all-trades index published monthly by INSEE on its 2010 base: 132.0 in January 2025, 134.7 in January 2026, a coefficient of 1.0205.

The global amounts quoted as examples, and any rents, charges or receipts expressed per year or per night, remain on their own basis: a building cost index does not apply to them.

To bring the ratios forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7). The BT01 measures contractors' input costs, labour at 44.9 % and materials at 36.5 %, not the prices actually tendered.