Higher-risk buildings: height and storey definitions
The 18 metre and seven storey tests are measured in a specific way, and planning Gateway One uses a different definition from the construction and occupation regimes. How to scope a borderline building.
A higher risk building definition question has two answers in England, and the one that applies depends on which part of the Building Safety Act 2022 framework you are in. For design and construction, a higher-risk building is one at least 18 metres in height or with at least seven storeys that contains at least two residential units, and also care homes and hospitals meeting the same height condition. For the occupation regime, care homes and hospitals drop out. For planning Gateway One, the test is different again and catches student and other educational accommodation. Three definitions, one building, and the measurement rules decide all of them.
Where the definitions sit in law
The Building Safety Act 2022 sets the framework and leaves the detail to regulations. The Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 describe the buildings in scope for the design and construction regime and contain the measurement rules for height and storeys.
Planning Gateway One sits somewhere else entirely. Article 9A of the Town and Country Planning (Development Management Procedure) (England) Order 2015 requires a fire statement with applications for development of a relevant building, and makes the Health and Safety Executive a statutory consultee.
Those are separate instruments with separate definitions. An architect who checks the 2023 Regulations and assumes the answer covers the planning application has skipped a step.
How height is measured
Height is measured from ground level to the floor surface of the top storey. Not to the ridge, not to the parapet, not to the top of the lift overrun.
Two refinements matter in practice. Where the ground is not level, the measurement is taken from the lowest ground level adjoining the external walls, which pushes sloping sites into scope more often than designers expect. And a storey consisting only of roof-top plant or machinery is ignored both for the height measurement and for the storey count.
The consequence is that a building can be well over 18 metres to its parapet and still sit outside the definition, or can look like a six-storey block and fall inside it because the ground falls away at the rear. Measure it properly before you rely on either outcome.
Storey counting and the exclusions
The storey count works on its own rules rather than on the architect's floor numbering.
| Element | Counted? |
|---|---|
| Storey wholly below ground level | No |
| Storey partly above ground level | Yes |
| Roof-top storey containing only plant or machinery | No |
| Mezzanine with internal floor area of at least half the largest storey | Yes |
| Gallery or small mezzanine below that proportion | No |
| Roof that is not a storey, for example a plant deck with no enclosure | No |
Seven storeys and 18 metres are alternatives, not a combined test. Either one brings the building into scope, which is why low floor-to-floor heights in residential schemes do not protect a seven-storey block.
Uses inside and outside the definition
For design and construction, the categories are buildings with at least two residential units, care homes and hospitals, each meeting the height condition. Hotels, offices, student blocks that are not residential units in the relevant sense, prisons and military barracks sit outside.
For the occupation regime that applies once the building is finished, care homes and hospitals are excluded and the focus is on buildings containing at least two residential units.
Gateway One is wider in one specific respect. Article 9A applies to a relevant building, which includes buildings containing two or more dwellings and buildings containing educational accommodation, meeting the height condition. Purpose-built student accommodation therefore engages the planning fire statement duty even where the later regimes treat it differently.
That asymmetry is the single most common error in scoping these schemes. Check each gateway against its own definition rather than carrying one answer forward.
Consequences at each gateway
- Gateway One, at planning application stage. A fire statement on the prescribed form must accompany the application, and the HSE is consulted. Without it the application should not be validated.
- Gateway Two, before building work starts. Building control approval must be obtained from the Building Safety Regulator rather than from a local authority or an approved inspector, and construction cannot lawfully begin until it is granted.
- Gateway Three, before occupation. A completion certificate from the Regulator is required, and the building must be registered before residents move in.
Programme effects follow from Gateway Two in particular, because the approval is a decision on a submitted design rather than a rolling inspection. Sequencing a start on site around it, and around the separate obligation to serve a commencement notice for levy purposes, needs care, as our note on commencement notices and the CIL amendment regulations explains.
Design changes during construction may need further approval, which is a different working method from the one most contractors are used to.
Interaction with the planning fire statement
The fire statement submitted at Gateway One addresses the fire safety considerations of the development as they relate to the land use and the layout: access and water supply for the fire and rescue service, the siting of the building, the arrangement of escape routes in principle, and the implications of the proposed design for later stages.
It is not a building regulations fire strategy and it should not pretend to be. The two documents have different audiences and the Gateway One submission is deliberately about the matters planning can control.
A Fire Statement is one of the report types where a competent professional is legally required rather than merely advisable. The requirement arises under the Building Safety Act 2022 framework and Article 9A of the Development Management Procedure Order, and the statement needs an author with the necessary fire-engineering competence. PlanScope can draft the structure and the policy framing of the document, and that draft is a starting point for that professional rather than a substitute. You can see how the fire-related reports sit alongside the rest of an application pack in the full list of report types.
Checking a borderline building
Where the answer is close, treat it as a survey exercise rather than a drawing exercise.
- Establish the lowest ground level adjoining the external walls from a topographical survey, not from an assumed datum.
- Measure to the finished floor surface of the top storey as designed, allowing for build-up that may change.
- List every storey and apply the exclusions one at a time, recording the reasoning.
- Calculate mezzanine areas against the largest storey rather than against the floor they sit within.
- Identify whether any roof-top enclosure contains anything other than plant, because a single residential unit or a roof terrace store can change the classification.
- Record the conclusion in a short note on file, dated, with the survey attached.
The reason for the written note is practical. Height is sometimes designed down to stay below a threshold, and if the scheme later gains 200mm of floor build-up or a raised plant plinth, someone needs to notice. A scheme that drifts into scope between planning and construction is an expensive discovery.
Reform news on the building safety framework and the wider 2023 planning changes is tracked on the UK planning law timeline. Enter your postcode on PlanScope to see which reports a residential scheme at this scale is likely to need.
This is general guidance, not legal advice. Check the position with your local planning authority, the Building Safety Regulator 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.
Frequently asked questions
Is height measured to the roof or to the top floor?
To the floor surface of the top storey, measured from ground level, and from the lowest ground level adjoining the external walls where the site slopes. A storey containing only plant or machinery at roof level is ignored. A building can exceed 18 metres to its parapet and still fall outside the definition.
Do seven storeys and 18 metres both have to be met?
No. They are alternatives, so either one brings a building into scope. That is why residential schemes with low floor-to-floor heights are not protected by being under 18 metres if they have seven storeys. Count the storeys using the regulations' own exclusions rather than the architect's floor numbering.
Does student accommodation count as a higher-risk building?
It depends which regime you are in. Planning Gateway One applies to relevant buildings under Article 9A of the Development Management Procedure Order, which include buildings containing educational accommodation that meet the height condition, so the fire statement duty is engaged. The construction and occupation regimes focus on residential units and treat the position differently.
When does a mezzanine count as a storey?
Where its internal floor area is at least half the internal floor area of the largest storey in the building. Smaller galleries and mezzanines are not counted. The comparison is against the largest storey, not against the floor the mezzanine sits within, which is a frequent error on warehouse and loft-style conversions.
What happens at Gateway Two?
Building control approval must be obtained from the Building Safety Regulator before construction begins, rather than from a local authority or an approved inspector. It is a decision on a submitted design, so the programme has to allow for it, and design changes during construction may require further approval before they are built.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.