Fire strategy for a mixed use building at planning stage

A mixed use fire strategy planning submission fails for a structural reason far more often than a technical one. The decisions that matter most are made on the plan, and the plan is fixed by the permission. Where the residential escape stair lands, whether the commercial unit sits under habitable rooms, how a kitchen extract duct gets from the ground floor to roof level, where a fire appliance can stand. None of that can be engineered away at building control stage without changing the drawings, and changing the drawings means going back to the council.

So the fire strategy has to be settled while the massing is still soft.

Separating the uses vertically

The basic principle is that a fire in the commercial unit should not threaten the flats above, and that a fire in a flat should not spread laterally or downwards into the commercial unit.

In practice this means a compartment floor between the uses, with every penetration through it treated. Every penetration. Structural connections, drainage stacks, electrical risers, gas supplies, ventilation ducts and the extract from a commercial kitchen. The last of those is the one that reshapes plans, because a kitchen extract duct serving a restaurant has to reach discharge level, has to be fire rated along its route, and has to be accessible for cleaning. Running it up the outside of the building creates an elevation problem. Running it internally takes a shaft out of the residential floor plate on every storey.

Refuse is the same story at smaller scale. Commercial waste, residential waste and recycling need separate stores, and a fire in a bin store is a common ignition source, so those stores want to be separated from escape routes and from the building envelope.

Shared cores and independent escape

Councils and the Health and Safety Executive both look hard at whether the residential occupants can leave without entering the commercial use, and whether firefighters can reach the residential floors the same way.

A single core serving both uses can work, but it generally needs a protected lobby arrangement that separates the two at every level, plus separate final exits. The floor area that takes is real. It is also smaller than the area lost in a redesign at Gateway Two, which is where these arrangements get tested properly.

Height drives the rest. The requirement for second staircases above 18 metres in residential buildings changes the core geometry rather than adding a component, and it interacts with firefighting shafts that already take a substantial bite out of each floor. Below that height, sprinkler provision above 11 metres brings a tank and pump room into the basement or ground floor plan, along with the access needed to maintain it.

Commercial plant and the risk it puts under the flats

Ground floor commercial uses arrive with plant. Refrigeration, air handling, gas-fired catering equipment, laundry, gym machinery, sometimes a generator. Each carries its own fire load and its own failure mode, and each has to be located, ventilated and separated.

Two arrangements cause most trouble. The first is plant at roof level serving a ground floor unit, which requires a service route through the residential building. The second is a gas supply to a commercial kitchen under dwellings, which brings explosion venting and isolation arrangements into the design conversation.

Neither is insurmountable. Both are much easier when the commercial unit's likely tenant is described at application stage rather than left as a blank Class E shell. A permission that says nothing about the intended use produces a fire strategy built on assumptions that the eventual tenant breaks.

Basements make all of this harder. Plant rooms, sprinkler tanks, commercial storage and car parking below ground each need their own escape provision and their own smoke clearance, and a basement car park under flats brings a fire load that has to be separated from the residential core. Where a basement is proposed on a constrained urban site, a Basement Impact Assessment deals with the ground and groundwater questions, and the fire strategy has to be read alongside it rather than after it.

Access for firefighting on a constrained frontage

Urban mixed use sites usually have one frontage, and it is usually busy.

Approved Document B sets out the vehicle access required for firefighting, including minimum road widths, turning provision, clearance heights and carrying capacity, and it requires hardstanding for a pumping appliance within 18 metres of the rising main inlet and within sight of the building entrance. Check the current edition rather than working from memory, because the document has been amended repeatedly.

On the site plan, show the appliance standing position, the route to it, the rising main inlet, the hydrant locations and any gate or bollard on the route. Where the standing position falls on the public highway, the highway authority becomes part of the conversation, and a loading bay or cycle stand in the wrong place can be the thing that stops the scheme.

What the fire statement has to cover

The statement is submitted on the form published by the Secretary of State and it addresses the principles rather than the detail. Site layout, emergency vehicle access, water supplies for firefighting, the approach to escape and evacuation, the construction method and materials in outline, and how the proposals affect surrounding land.

The Fire Statement is a planning document, but the Health and Safety Executive reviews it as a statutory consultee at Planning Gateway One, and an inadequate one delays validation and determination. It is required to be prepared by someone with the necessary fire engineering competence under the framework established by the Building Safety Act 2022 and Article 9A of the Development Management Procedure Order 2015. The same is true of a Fire Safety Strategy prepared to BS 9991 or BS 9999. An AI-assisted draft gives that professional a structured starting point and their own judgement remains legally required.

What is deferred and what is locked

Detailed fire engineering, compartment construction, detection and alarm design, smoke control sizing, sprinkler hydraulics and the fire safety case all belong to the later gateways and to the building regulations process. Nothing in a planning permission settles them.

But the permission locks the geometry. Height, stair count, core position, shaft positions, the compartment line between uses, the appliance standing area and the elevation treatment. If any of those turns out to be wrong at Gateway Two, the fix is a section 73 application or a fresh permission, with the programme cost that implies.

Work the fire strategy alongside the massing study rather than after it. On a mixed use scheme the honest sequence is to sketch the core, the compartment line and the appliance standing position on the first massing option, then test whether the floor area still works. Teams that do it the other way round tend to discover the problem at the point when the drawings have already been issued for planning. For specialist technical reports, qualified professional input may be required. This is general guidance rather than 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. We do not guarantee planning approval.