How gross internal area is measured for the levy

The Community Infrastructure Levy is charged on the gross internal area of the chargeable development, and the figure that matters is not the one in the sales particulars. GIA is measured to the internal face of the perimeter walls at every floor level, and it includes things architects habitually leave out of a schedule of accommodation: garages, plant rooms, stair enclosures, risers and basements. Getting the measurement wrong by a few square metres on a single house is irritating. Getting it wrong across a 60-unit scheme can cost tens of thousands of pounds, and the liability notice arrives long after the fee proposal has been agreed with the client.

What the Regulations charge and what they do not define

The Community Infrastructure Levy Regulations 2010 set the chargeable amount by reference to the gross internal area of the chargeable development, in square metres, multiplied by the rate in the charging schedule and indexed.

What the Regulations do not do is define gross internal area. There is no measurement code in the statutory instrument. Collecting authorities in practice apply the definition in the RICS Code of Measuring Practice, and that is what most CIL additional information forms assume. RICS Property Measurement and the international property measurement standards serve different purposes and produce different numbers, so state on the form and on the area schedule which definition you have used. An officer who cannot tell which basis you measured on will ask, and that costs a fortnight.

Because the definition is conventional rather than statutory, a disagreement about measurement is a disagreement about the application of the Code to your drawings. It is resolvable, and the route for resolving it is set out at the end of this article.

Measuring to the internal face

Measure each floor horizontally to the internal face of the enclosing perimeter walls. The thickness of the external wall is excluded. External projections, such as a projecting pier or an external flue, are excluded with it.

Where the floor is raked or stepped, as in an auditorium, it is measured horizontally as though it were level. Where a floor is structurally raked and there is a usable horizontal floor beneath it with permanent access, that lower floor counts as well.

Atria and double-height entrance halls are measured at base level only. The void above them is not counted again, which is the one place the convention works in your favour on a scheme with a tall entrance.

Internal open-sided balconies and walkways inside the building envelope are included. External open-sided balconies are not.

Internal walls, risers, stairs and plant

Everything inside the perimeter counts, whether or not anyone can use it.

• Internal walls and partitions, including their thickness
• Columns, piers, chimney breasts and other internal projections
• Stairwells and lift wells, including the void over them on upper floors
• Vertical service ducts and risers
• Lift motor rooms, plant rooms, tank rooms and fuel stores housed in a permanent covered structure, whether or not they sit above the main roof line
• Toilets, lobbies, bathrooms, showers, changing rooms and cleaners' cupboards
• Corridors of a permanent essential nature
• Mezzanine floors with permanent access

The rooftop plant enclosure is the one most often missed. A screened plant deck with a permanent roof over it is a covered structure of a permanent nature, and its footprint is part of the GIA. An open screened deck with no roof is not.

Risers are the second most common omission, because they are drawn as hatched boxes and read as structure rather than as floor area. Add them up. On a ten-storey residential building, four risers at a square metre each come to 40 square metres, which is a real number at most charging rates.

Garages, basements and loft space

Garages are included in GIA. This surprises householders and quite a few architects, and it is the single most common reason a domestic extension scheme comes in above a relief threshold.

Basements are floors and are measured in the same way as any other level. A basement plant room, a basement car park within the building envelope, and a basement storage area all count. An open ramp down to the basement is a different matter, because it is not enclosed.

Loft space is the awkward case. A loft with permanent access, such as a fixed staircase, is a floor. The Code includes areas with a headroom of less than 1.5 metres within GIA, which on a shallow pitch roof can add area nobody expected, and collecting authorities take different views on how to treat an unconverted void reached only by a hatch and a ladder. State your assumption on the drawing and on the form, so that any disagreement is visible at the start rather than at the liability notice.

Conservatories and pavement vaults are included. Greenhouses, garden stores and detached fuel stores at a dwelling are excluded.

Covered but unenclosed areas

The dividing line runs along the building envelope, and the Code resolves most of it.

The cases that still cause argument are partly enclosed. A bin store with three walls and a roof, open on the fourth side, will usually be treated as covered and enclosed enough to count. A bike shelter with a roof on posts will not. If the scheme has several of these, measure them, list them separately, and say which you have included and why.

Deducting existing floorspace

Where an existing building is being demolished or converted, its gross internal area can be deducted, which often reduces the chargeable amount to nothing on a replacement dwelling of similar size.

The condition is use. The Regulations allow the deduction where the relevant building contains a part that has been in lawful use for a continuous period of at least six months within the three years ending on the day planning permission first permits the chargeable development. A building empty for four years does not qualify, however substantial it is, and that single provision has caught a great many conversion schemes.

Evidence of use is therefore worth assembling early: council tax or business rates records, utility bills, tenancy agreements, photographs with metadata, trading accounts. Submit it with the additional information form rather than waiting to be asked.

Measure the existing building on the same basis as the proposal. An existing-building GIA that excludes the garage while the proposed GIA includes it produces an inflated net figure, and that is the applicant's error, not the authority's.

Reconciling the measurement with the drawings

Three different area figures usually circulate on a project, and they should all be reconcilable on one sheet.

1. GIA for the levy and for the planning application forms.
2. Net internal area or net sales area for the appraisal and the agent.
3. Gross external area, where a contractor or a cost consultant is working from it.

Put them in a table on the area schedule drawing, floor by floor, with a short note of what is included in each. The habit pays for itself when the collecting authority queries the figure, when the viability appraisal is tested, and when the quantity surveyor asks why the rate per square metre looks odd. The way floor areas feed an appraisal is covered in the note on space standards and accessible housing as appraisal inputs, and the presentation conventions in the note on viability appraisal submission format.

Keep the measurement in a spreadsheet tied to the drawing revision. When the plans change at the eleventh hour, the area schedule has to change with them, and a liability notice calculated from a superseded revision is a problem that takes months to unwind.

Where the figure is wrong and how it is challenged

The collecting authority issues a liability notice stating the chargeable amount. If you think the measurement is wrong, there is a two-stage route and both stages are short.

First, request a review by the collecting authority. The Regulations allow this within 28 days of the liability notice being issued, and the authority reconsiders its own calculation. Second, if the review does not resolve it, appeal the chargeable amount to the Valuation Office Agency, which the Regulations allow within 60 days of the liability notice. Separate appeal routes exist for apportionment, for the various reliefs and exemptions, and for surcharges.

Miss those windows and the amount stands. There is no general discretion to revisit it later, and paying under protest does not preserve a right of appeal.

The honest caveat is that measurement disputes are usually about interpretation at the margins rather than arithmetic, and a well-documented area schedule submitted at the outset prevents most of them. Where the chargeable amount is large enough to affect the scheme, the measurement deserves the same attention as the viability assessment and the affordable housing statement that sit alongside it.

Enter your postcode on PlanScope to see which supporting documents your scheme is likely to need.

This is general guidance, not legal advice. Charging rates are set locally and indexed annually, so check the current charging schedule and the authority's own guidance before relying on any figure. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.