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Calculating CIL and Measuring Gross Internal Area

Calculating CIL

CIL is calculated per square metre of additional floorspace using the gross internal area (GIA) of the proposed development. It applies to those types of development identified in the CIL Charging Schedule.

In calculating CIL, consideration will be given to any existing floorspace on site. Where existing floorspace is being re-used or demolished it may be deducted from the CIL liability provided it has been in continued lawful use for at least six months in the last three years.

The Council will calculate the amount of CIL payable (the chargeable amount) on a chargeable development in accordance with the formulae set out at Regulation 40 of the Community Infrastructure Levy Regulations 2010 (as amended).

The CIL charge per sqm applies to the entire GIA for new dwellings and extensions exceeding 100 sqm, meaning that the whole floorspace is charged and not just the amount over 100 sqm.

Measuring the Gross Internal Area (GIA)

Floorspace is measured according to the Royal Institute of Chartered Surveyors (RICS) Code of Measuring Practice for Gross Internal Area (GIA).

Residential floorspace includes new dwellings, extensions, conversions, garages or any other buildings ancillary to residential use.

Generally, any structure with three walls and a roof can be a building with internal floorspace and is therefore chargeable under CIL.

GIA is the internal area of the building, and should include:

  • area occupied by internal walls and partitions, chimney breasts, stairwells, lift wells, vertical ducting and the like,
  • all rooms including conservatories,
  • atria, entrance halls, circulation space, corridors and communal entrances,
  • toilets, toilet lobbies, bathrooms, showers, changing rooms, cleaners’ rooms and the like,
  • garages and loading bays,
  • storage,
  • plant rooms, fuel storage, tank rooms and the like, including those on the roof,
  • basements,
  • internal open sided balconies, walkways and the like,
  • ancillary floorspace (eg underground parking).

The following will be excluded from CIL liable floorspace:

  • buildings into which people do not normally go (including buildings into which people go intermittently for the purpose of inspecting or maintaining fixed plant machinery),
  • conversion of one dwelling into two or more dwellings (including conversion from a single house into flats),
  • perimeter wall thicknesses and external projections,
  • external open-sided balconies, covered ways and fire escapes,
  • canopies,
  • voids over or under structural, raked or stepped floors,
  • floorspace resulting from demolition or change of use can be deducted from the CIL charge if:
    • it has been in continuous lawful use for at least six months in the three years prior to a development being permitted;
    • on the day planning permission is granted the floor space of the existing building exists; and
    • the existing building is demolished before completion.
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