Fire strategy for a residential block above commercial units

A mixed use block fire strategy has to reconcile two buildings that happen to share a structure. Flats above are designed around a stay put principle, protected entrance halls and compartmentation between dwellings. A shop, restaurant or gym below is designed around simultaneous evacuation, travel distances to a final exit and a fire risk assessment under the Fire Safety Order. Putting one on top of the other produces a set of interface problems that shape the plan, the core position and the servicing arrangement, all of which appear on the planning drawings.

The strategy work belongs to a fire engineer. A Fire Safety Strategy to BS 9991 or BS 9999 and a Fire Statement at Planning Gateway One both require an author with the necessary fire-engineering competence, and any AI-assisted draft is a starting point for that professional rather than a replacement.

Why mixed use complicates the strategy

Approved Document B is published in two volumes, one for dwellings and one for buildings other than dwellings. A block of flats above commercial floorspace needs both, applied to different parts of the same structure, with a defined boundary between them.

The evacuation philosophies differ. Residents of flats are normally expected to remain in their dwelling unless directly affected, relying on compartmentation to contain a fire for long enough. Commercial occupants evacuate on the alarm. A single alarm system covering both would either evacuate the flats unnecessarily or fail to alert the shop.

The occupancy differs too. Residents sleep, are sometimes unfamiliar with the building's escape arrangements, and include people who cannot self-evacuate. Commercial occupancy is awake, supervised and, in a workplace, trained.

So the building is designed as two separate fire entities with a hard boundary between them. Every decision that follows is about keeping that boundary intact.

Separating residential and commercial escape

The starting requirement is that the flats have their own means of escape, independent of the commercial floorspace. Residents should not have to pass through a shop, a restaurant, a back-of-house corridor or a shared lobby serving both uses to reach the street.

In practice that means a dedicated residential core with its own entrance at ground level, a protected stair, and a protected lobby arrangement at each residential floor. The core has to land somewhere on the frontage, which competes directly with the commercial units for the most valuable street elevation. On a narrow urban plot this is the decision that shapes the whole ground floor plan.

A few consequences follow that designers should price early. The residential entrance needs step-free access, an intercom, a post arrangement and space for cycles and refuse, none of which can open directly into the protected stair. The stair must be kept clear, so storage and services cannot be tucked into it. And where the ground floor unit wraps the core, the compartment walls around the stair have to be continuous through the shopfront zone.

Where the site also carries a basement, the interface gets harder still, since a basement serving the commercial unit should not connect to the residential stair. Basement design brings its own structural and ground questions covered in Eurocode 7 and geotechnical evidence.

Compartmentation between the uses

The floor separating the commercial and residential parts is a compartment floor, and the walls separating the two occupancies are compartment walls. The period of fire resistance depends on the height of the building and the use, and it is one of the numbers the fire engineer fixes early because it drives the structural depth.

Three details cause most of the problems on site.

First, the junction between the compartment floor and the external wall. A gap at the slab edge behind a rainscreen or a curtain wall defeats the compartment floor entirely, so cavity barriers and fire stopping at that junction have to be drawn, not noted.

Second, the shopfront. A commercial unit with a tall glazed frontage sitting below a residential window creates a route for fire to break out and re-enter above. Spandrel height, glazing performance and the depth of any projecting element above the shopfront all matter here.

Third, any structural element supporting the residential floors that passes through the commercial space. A column inside a restaurant is carrying flats, and its fire protection has to reflect that, which often conflicts with the tenant's fit-out ambitions.

Service risers crossing the boundary

Services want to run vertically. Compartmentation wants them not to.

The cleanest arrangement is separate risers for each use, each within its own protected shaft, with no commercial service passing through a residential protected route. That is rarely achievable in full, so the strategy has to identify each crossing and specify the fire stopping and, where relevant, the fire dampers at every compartment line.

The commercial kitchen extract duct is the recurring problem. A restaurant at ground floor needs its extract to terminate at roof level, which means a duct rising through or alongside the residential building for its full height. It has to be fire rated for the compartments it passes, accessible for cleaning, and isolated from residential accommodation. It also has to terminate high enough and far enough from openable residential windows to satisfy the odour assessment, which is why the Ventilation and Extraction Statement and the fire strategy should be coordinated rather than written separately.

Plant noise transmitted into flats is a third strand of the same problem, dealt with through a Noise Impact Assessment and normally conditioned.

Servicing, refuse and plant interfaces

Refuse stores are a fire risk and a management problem. Residential and commercial waste should be stored separately, in fire-rated enclosures, not opening into a protected escape route, and positioned so collection vehicles can reach them without blocking fire appliance access.

Fire service access has its own geometry. Appliance access roads, hardstanding, hydrant positions and, above a threshold height, a firefighting shaft with a firefighting lift all take up space at ground level and on the site plan. Where a scheme squeezes commercial servicing, residential refuse, cycle parking and fire appliance access into one yard, something usually gives, and it is better for that to happen at design stage than at technical approval.

Management responsibilities after completion

The strategy only works if someone maintains it, and in a mixed use building the responsibility is split.

Under the Regulatory Reform (Fire Safety) Order 2005 the responsible person for the commercial premises is the occupier or employer, while the common parts of the residential element fall to the building's managing agent or freeholder. The Fire Safety (England) Regulations 2022 add duties in blocks of flats, and where the building is higher risk under the Building Safety Act 2022 an accountable person carries further obligations.

The practical risk is a commercial tenant fitting out in a way that breaches the compartment line, propping a fire door, or storing waste against the residential core. Lease drafting is the control, and it sits outside the planning process, but a fire strategy that ignores the management model is incomplete.

What the planning submission should show

Planning is not building control, so the submission does not need a full fire engineering design. It does need to show that the arrangements are deliverable within the consented form.

At minimum the drawings should show the separate residential entrance and core with its route to the street, the commercial unit boundaries and their final exits, the location of refuse and cycle stores for each use, the extract duct route and its termination point, plant locations, and fire appliance access with any required hardstanding.

Where the building is a relevant building, a fire statement must accompany the application under the Development Management Procedure Order and the Health and Safety Executive is consulted at Planning Gateway One. A requirement for a second staircase in new residential buildings above 18 m has been confirmed for England with transitional arrangements, so check the current Approved Document B text and the applicable transitional dates before fixing the core layout, because retrofitting a second stair after permission changes the plan from the ground up.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission, and fire documents require an author with fire-engineering competence. We do not guarantee planning approval. To see which documents a mixed use scheme is likely to need, enter your postcode on PlanScope.