Fire narratives for volumetric and modular residential

A modular construction fire statement has to answer a question that a traditionally built scheme never raises: what happens in the gaps between the boxes. Volumetric modules arrive as completed rooms with their own floors, ceilings and walls, so stacking them creates horizontal and vertical cavities that do not exist in an in-situ frame. Those cavities are the first thing a fire engineer looks for and the first thing the Building Safety Regulator will ask about.

None of that stops a modular scheme getting permission. It does change what the planning submission has to say, and it changes when the manufacturer has to be in the room.

Which buildings fall into Gateway One

Article 9A of the Town and Country Planning (Development Management Procedure) (England) Order 2015 requires a fire statement to accompany an application for planning permission for development involving a relevant building. In broad terms that means a building containing two or more dwellings, or educational accommodation, which meets the height condition of 18 m or more, or seven or more storeys.

The statement must be submitted on the form published by the Secretary of State, and the Health and Safety Executive, acting as the Building Safety Regulator, is a statutory consultee on those applications. Its response has to be taken into account before the authority determines the application.

A fire statement is a document that calls for fire-engineering competence. The legislation expects it, the Regulator reads it as the work of someone with that competence, and an AI-assisted draft is a starting point for that professional rather than a substitute for them.

Interfaces between modules and the cavity question

In a volumetric building the compartment lines fall at module boundaries, which means every compartment wall and floor has a construction joint running along it. The fire risks that follow are well understood by the people who design these systems and poorly understood by everyone else.

The matters a fire strategy has to address:

• Cavity barriers at the junction between adjoining modules, horizontally and vertically.
• The sealing of inter-module voids where services cross a compartment line.
• Fire stopping installed on site rather than in the factory, and who inspects it.
• The behaviour of the system where modules meet a traditionally built core or podium.
• Tolerance gaps that are designed in to allow modules to be craned into position.

The last point is the awkward one. A tolerance gap exists because the construction method needs it, and it has to be filled with something that performs when hot and that can be installed through a narrow opening after the modules are set. That is a system-specific answer, not a generic one.

Factory assurance and the evidence trail

The attraction of offsite manufacture is consistency. The same attraction is what makes the assurance regime so central, because once a module leaves the factory you cannot open its walls to inspect them.

What a credible evidence trail looks like at planning stage: the system is identified, the manufacturer's factory production control arrangements are described, third-party certification or accreditation of the system is referenced, and the arrangements for traceability of each module are set out. The Building Safety Act 2022 framework and the golden thread of information expect that record to exist from the start rather than be assembled at handover.

Where the procurement route has not been settled, say so. A statement that names a specific system the client has not yet appointed is worse than one that sets out performance requirements the eventual system must meet.

External wall build-up on a modular system

Modules are normally clad after installation, or partly clad in the factory with a site-applied outer layer. Either way, the external wall is a composite of factory and site work, and the combustibility restrictions for relevant buildings apply to it in the same way as to any other.

Two practical points follow for the planning drawings. The wall build-up depth is fixed earlier than on a traditional build, because the module dimensions are fixed, so the elevations and the reveals are less adjustable later. And where the facade zone is shallow, the material palette narrows, which can push a scheme towards finishes that the design officer did not expect.

That is why the elevational conversation and the fire conversation have to happen together on these schemes. A design officer asking for deeper reveals and a fire engineer asking for a non-combustible build-up are both reasonable, and reconciling them after permission is expensive.

What the planning submission can and cannot settle

Gateway One is about the matters that planning can actually control, which is a narrower list than people assume. The fire statement covers site layout, access for fire appliances, water supplies for firefighting, the principles of the means of escape and the principles of the fire safety design.

It does not approve cavity barrier details. Those belong to Gateway Two and the building control process under the Regulator.

The stair row matters more than it looks. The number and position of staircases is drawn on the planning drawings, and the requirement for a second staircase in new residential buildings above 18 m, introduced by amendment to Approved Document B with transitional arrangements, changes the floor plate. Verify the current transitional position before fixing a core layout, because adding a stair after permission alters unit numbers, areas and the viability case.

A Fire Statement handles the Gateway One submission itself. The fuller Fire Safety Strategy to BS 9991 or BS 9999 is a fire-engineering document and sits alongside it on more complex schemes. Both require a competent author, and PlanScope's drafts are a structured starting point for that author.

Programme is the other planning consequence. Module production slots are booked months ahead, and a manufacturer will not hold a slot for a scheme whose permission is still subject to a Regulator response. Build the Gateway One consultation into the programme as a fixed period rather than an optimistic one, and expect the authority to use an extension of time if the response arrives late.

Risks worth disclosing rather than hiding

Three disclosures improve a modular submission rather than weakening it.

State whether the module system has been selected. If it has not, set out the performance requirements and the stage at which the system will be fixed, and accept a condition requiring the detailed fire strategy to reflect the selected system.

State where site-installed fire stopping occurs and how it will be inspected and recorded. The Regulator is looking for an answer that includes a named inspection regime rather than a promise.

State the interface between the modular element and any traditionally built core, podium or basement, because that junction is where two sets of assumptions meet.

Scheme information also has to be available to the fire service in operation, which is why the secure information box and its position appear on drawings at planning stage on taller residential schemes.

Enter your postcode on PlanScope to see which reports a residential scheme of this height is likely to need, then brief the fire engineer against that list.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.