Measuring height for the 18 metre fire statement threshold

Getting the 18 metre height measurement for fire statement purposes wrong is a validation failure, and it happens because people measure to the parapet. The convention is to measure from ground level to the floor surface of the top storey, ignoring any storey that is a roof-top machinery or plant area or consists exclusively of plant rooms. A 19 m parapet over an 17.4 m top floor is not a relevant building on height alone.

Two separate tests sit behind the requirement, and either one triggers it. Height of 18 m or more. Or seven or more storeys. A six-storey building can qualify on height, and a seven-storey building qualifies whatever its height.

Where the threshold is defined

Article 9A of the Town and Country Planning (Development Management Procedure) (England) Order 2015 requires a fire statement, on the form published by the Secretary of State, with applications for planning permission involving a relevant building. Relevant buildings are those containing two or more dwellings or educational accommodation that reach the height or storey threshold.

The fire statement is a validation requirement, so an application submitted without it, or with a statement on the wrong form, can be returned as invalid. The Health and Safety Executive is the Gateway One statutory consultee and will see the statement.

Keep this test separate from the higher-risk building test used at Gateways Two and Three. The Building Safety Act 2022 and the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 define higher-risk buildings for building control purposes, with their own treatment of storeys and height. The two regimes use similar language and are not interchangeable, so read the wording that applies to the consent you are seeking.

The datum the measurement is taken from

Measurement runs from ground level to the floor surface of the top storey. Not to the ceiling. Not to the parapet. Not to the top of the lift overrun.

Where the ground around the building is not level, the measurement is taken from the lowest part of the ground adjacent to the building. The same convention appears in Approved Document B, which defines the height of a top storey as its floor surface height above ground level on the lowest side of the building, excluding a top storey consisting exclusively of plant rooms.

That lowest-side rule is where sloping sites catch people. A building whose top floor sits 17.2 m above the entrance level on the high side may sit 18.6 m above the ground at the opposite corner, and it is the second figure that counts. On any site with more than a metre of fall, measure from each corner before you settle the floor levels.

Formed ground is the related trap. If the landscape design lowers the external level to create a lightwell, a terrace or a ramped basement access against the building, the lowest adjacent ground level moves with it. A scheme that cleared the threshold on the architectural sections can cross it when the landscape package is issued.

What counts as a storey

The storey count is the second route to the threshold, and it is counted differently from the height.

Roof-top plant and machinery storeys are left out. A plant enclosure at roof level, screened and containing only equipment, is not a storey for this purpose, and the same exclusion applies to the height measurement.

Mezzanines are the awkward category. The higher-risk building regulations include a mezzanine in the storey count only where its internal floor area is at least half the internal floor area of the largest storey that is not a mezzanine. A small gallery over a double-height entrance does not add a storey. A floor plate covering two thirds of the footprint does.

Storeys below ground level are generally excluded from the count. That is a sensible rule and a poor assumption to carry into design, because "below ground level" on a sloping site is not obvious, and a lower ground floor that is fully exposed on one elevation is not a basement.

Buildings that sit within a metre of the limit

Four moves give control over a marginal case, and all four belong in the early stages rather than at technical design.

1. Set the top storey finished floor level deliberately, against the lowest external ground level, and treat it as a fixed constraint in the structural zone coordination.
2. Keep plant at roof level exclusive to plant, with nothing else in the enclosure. A plant enclosure that also contains a cycle store, a tank room used for anything else, or circulation serving a roof terrace stops being excluded.
3. Fix the external levels before the planning submission, in the drawings rather than the landscape narrative, and lock them with a condition if the authority is willing.
4. Decide in advance what happens if the building ends up over the line. Designing a scheme that works both ways costs less than redesigning one that does not.

A scheme intentionally designed to sit just under the threshold deserves a candid note in the fire statement or the design statement explaining the measurement. Officers and consultees see this constantly, and an unexplained 17.9 m invites exactly the scrutiny the design was trying to avoid. Set out the datum, the dimension and the reasoning.

Recording the measurement on the drawings

Annotate the section that governs, not the prettiest one. It needs the external ground level at the lowest point adjacent to the building as a spot level to the site datum, the finished floor level of the top storey as a spot level, the dimension between them, and a note stating the calculated height and the exclusion applied to any roof-top plant.

Add a storey schedule listing every floor plate with its area, flagging mezzanines and their area as a proportion of the largest non-mezzanine storey, and marking which storeys are excluded from the count and why. That single sheet answers the validation officer's question and the consultee's question without correspondence.

Where the application involves an existing building rather than a new one, survey the building rather than relying on record drawings. Floor-to-floor dimensions in a 1960s block are rarely what the original drawings say, and an added screed or a lowered pavement changes the answer. A measured survey alongside the structural appraisal of a building proposed for retention gives you both pieces of evidence at once.

Who prepares the statement

A Fire Statement for a relevant building requires fire-engineering competence. The regime under the Building Safety Act 2022 framework and article 9A of the Development Management Procedure Order assumes an author who can speak to means of escape, access and water supplies for firefighting, and the construction products and materials used. A professional with that competence is legally required, and an AI-assisted draft is a starting point for that person rather than a substitute for them.

The same is true of a Fire Safety Strategy prepared to BS 9991 or BS 9999, which is a fire-engineering document throughout. Where you need someone to review and sign off a draft, the professional directory is the route to a reviewer.

And brief that person on the height measurement explicitly. The commonest version of this problem is a fire engineer who assumes the building is below the threshold because the architect said so, and an architect who assumed it because the parapet is 17.5 m above the entrance.

Note: crossing the threshold adds more than a document. It brings the Health and Safety Executive in as a consultee, stretches the determination period in practice, and affects the building control route later. Treat the measurement as a programme item.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.