Compartmentation drawings in a fire safety strategy

A compartmentation drawing fire strategy set is the part of a fire safety strategy that a planning layout can actually break, which is why it belongs in the design process rather than at the end of it. The drawings show where compartment walls and floors run, what fire resistance period each one achieves, where protected stairs and lobbies sit, how far a resident has to travel to reach one, and how the fire service gets to the building and up it. Get the core positions and the access geometry wrong at planning stage and the scheme either loses units or needs a new application.

Note the distinction that trips people up. The Fire Statement required at Planning Gateway One is a planning submission on a prescribed form. The fire safety strategy is the fuller fire engineering document that sits behind it and continues into building control.

What the drawing set has to show

A strategy for a residential block usually carries a plan per storey plus at least one section, and each plan needs to communicate several layers without becoming unreadable.

The content that a reviewer looks for: compartment walls and floors identified with their fire resistance periods, protected shafts including stairs, lifts and service risers, fire doors with their ratings and whether they are self-closing and smoke sealed, cavity barriers and the extent of concealed spaces, escape routes with travel distances annotated, final exit positions, the firefighting shaft where one is required, rising main inlet and landing valve positions, sprinkler or other suppression coverage, smoke control provision and its type, fire service vehicle access and hardstanding, hydrant locations, and the assembly point.

Use a consistent convention and put the key on every sheet. Heavy line weights for compartment lines with the period written in, a distinct hatch for protected routes, and door tags that match the door schedule. A drawing that requires the reader to hold three sheets side by side has failed at its job.

On a refurbishment, record what exists before designing what is proposed. The same discipline that goes into condition grading and defect schedules applies to surveying existing compartmentation, because assumptions about a 1960s block's separating construction are usually wrong.

Compartment lines and fire resistance periods

Compartmentation divides the building so that a fire in one part does not spread to another before the occupants are out and the fire service has intervened. In a block of flats, each dwelling is a compartment, and the separating walls and floors have to achieve a stated period of fire resistance for loadbearing capacity, integrity and insulation.

The periods scale with height. Approved Document B sets out minimum periods for blocks of flats by the height of the top storey, running from 30 minutes on the smallest buildings through 60 minutes up to 18 metres, 90 minutes up to 30 metres, and 120 minutes above that. Treat those as indicative and read the current tables, because the document has been amended repeatedly and the figures interact with sprinkler provision.

Three things the drawings must resolve rather than assume. Every service penetration through a compartment line needs a stated sealing detail. Every junction between a compartment wall and the external wall or the roof needs to maintain the line, which is where cavity barriers come in. And any partial-height compartment wall or transfer structure needs its protection period shown, because a protected shaft loses its rating at the weakest connection.

Where the strategy departs from the Approved Document and uses a fire engineering approach under BS 7974 instead, the drawings have to carry the assumptions the analysis relied on. Those assumptions become conditions of use for the building's life.

Protected routes and travel distances

Travel distance is the figure that most often collides with a planning layout. In a block of flats, travel in a single direction within the common parts is tightly limited, in the order of 7.5 metres from a flat entrance door to the protected stair or to a point of alternative escape, while a distance of up to 30 metres is accepted where escape is available in more than one direction.

That single figure dictates how many flats a single-stair core can serve on each floor, which dictates the efficiency of the whole building. Test it on the concept plan. A corridor drawn to suit the unit mix and then measured afterwards is how schemes lose a flat per floor.

Within a dwelling there are separate limits on travel to the flat entrance door, and open-plan layouts with the kitchen on the escape route need particular attention, usually through enhanced detection, sprinklers or a protected entrance hall.

Annotate the distances on the drawing with the measured route shown as a polyline, going around furniture zones and through door swings rather than as a straight line. Reviewers check this.

Firefighting shafts and access for appliances

Firefighting provisions come in at height and at depth. A firefighting shaft, comprising a firefighting stair with protected lobbies and, above a certain height, a firefighting lift and a rising main, is required where a storey is a set distance above or below fire service access level, and the usual triggers are 18 metres above and 10 metres below. Basements change the answer more often than people expect, so a deep basement car park under a modest building can pull the requirement in.

Vehicle access is a planning matter as much as a building regulations one, because it sets road widths, turning provision and hardstanding positions in the site layout. Approved Document B gives minimum dimensions for access routes, including a carriageway width of 3.7 metres between kerbs, gateway width of 3.1 metres and a carrying capacity for a pump appliance of 12.5 tonnes, together with a maximum hose distance from the appliance to points within the building. Check the current table rather than working from memory, and check whether a high reach appliance is required, because its turning circle and loading requirements are considerably greater.

Then reconcile that with the soft landscaping drawing. Fire service hardstanding under a tree canopy, across a permeable paving system not designed for the load, or over a shallow attenuation tank, is a coordination failure that surfaces at technical approval.

External walls and the cladding question

External wall construction now sits at the centre of any strategy for a residential building. The strategy has to state the classification of the materials in the external wall build-up, the combustibility restrictions applying at the building's height, and the approach to cavity barriers, balconies and any attachments.

For a building in scope of the higher-risk regime, meaning 18 metres or seven storeys with at least two residential units, the strategy also has to be written knowing that the Building Safety Regulator will examine it at the later gateways. Decisions taken for planning reasons, such as a deep balcony, a projecting brise soleil or a heavily articulated facade, carry fire consequences, and testing them now costs far less than testing them later.

Say plainly in the strategy what is not yet fixed. A statement that the external wall specification is subject to test evidence, with the performance requirement stated, is honest. A statement that the wall will comply is not information.

Coordinating fire strategy with the planning layout

The items that have to be agreed before the planning drawings are finalised are few and they are all structural to the scheme.

1. Number and position of stair cores, including whether a second staircase is required at the building's height under the current version of Approved Document B and its transitional arrangements.
2. Corridor lengths and the resulting units per core per floor.
3. Basement extent and its effect on firefighting shaft requirements.
4. Fire service access route, turning provision and hardstanding positions, coordinated with levels, drainage and planting.
5. Rising main inlet positions, which need to be accessible from the appliance position and are usually a facade decision.
6. Sprinkler or suppression strategy, since a tank and pump room takes real floor area.

Bring these into the Design and Access Statement as design drivers rather than leaving them as technical appendices. A case officer who understands why the core sits where it does will defend the layout in the committee report.

Who is competent to author the strategy

A fire safety strategy prepared to BS 9991 for residential buildings, or BS 9999 for other buildings, is a fire engineering document and a professional with fire engineering competence is legally expected to prepare it. The same is true of the Fire Statement required at Planning Gateway One under Article 9A of the Development Management Procedure Order 2015, where the Health and Safety Executive acts as statutory consultee for relevant buildings.

Look for chartered engineer status with the Institution of Fire Engineers, evidence of work on buildings of comparable height and use, and a clear statement of which standard the strategy follows. Ask who will sign it and whether their professional indemnity cover extends to the approach being used, particularly where a fire engineering analysis departs from the Approved Document.

A Fire Safety Strategy drafted with AI assistance is a starting point for that fire engineer to develop, check and take responsibility for. It is never a substitute for their judgement, their calculations or their signature. Arranging independent review through the professional directory before submission is the sensible order of work.

This is general guidance rather than legal advice, so 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. For specialist technical reports, qualified professional input may be required.