Guidance

Code of measuring practice: definitions for rating purposes

Published 2 October 2012

Gross external area (GEA)

Broadly speaking the whole area of a building taking each floor into account.

GEA will include:

• perimeter wall thickness and external projections
• areas occupied by internal walls (whether structural or not) and partitions
• columns, piers, chimney breasts, stairwells, lift wells etc
• lift rooms, plant rooms, tank rooms, fuel stores, whether or not above roof level
• open-sided covered areas (should be stated separately)

GEA will exclude:

• open balconies
• open fire escapes
• open sided covered ways
• Open vehicle parking areas, terraces and the like
• minor canopies
• any area with a headroom of less than 1.5m (except under stairways)
• any area under the control of service or other external authorities

Note that:

• party walls are to be measured to their centre lines
• the areas of items excluded from GEA, should be calculated and shown separately

Gross internal area

Broadly speaking the whole enclosed area of a building within the external walls taking each floor into account and excluding the thickness of the external walls.

GIA will include:

• areas occupied by internal walls (whether structural or not) and partitions
• service accommodation such as WCs, showers, changing rooms and the like
• columns, piers, whether free standing or projecting inwards from an external wall, chimney breasts, lift wells, stairwells etc
• lift rooms, plant rooms, tank rooms, fuel stores, whether or not above roof level
• open-sided covered areas (should be stated separately)

GIA will exclude:

• open balconies
• open fire escapes
• open-sided covered ways
• open vehicle parking areas, terraces and the like
• minor canopies
• any area with ceiling height of less than 1.5m (except under stairways)
• any area under the control of service or other external authorities

Note that the areas excluded from GIA should be calculated and shown separately.

Identification of separate buildings

Because GIA excludes the thicknesses of external walls, but includes the thicknesses of all internal walls, it is important to identify what constitutes a separate building.

The general rule to be adopted is that elements, which are not united in a common form of construction, should be regarded as separate buildings. But where contiguous elements are of a similar construction they should be treated as a single building providing that more than 50% of the party wall has been removed.

Net Internal Area (NIA)

Broadly speaking the usable area within a building measured to the face of the internal finish of perimeter or party walls ignoring skirting boards and taking each floor into account

NIA will include:

• perimeter skirting, moulding, or trunking
• kitchens
• any built in units or cupboards occupying useable areas (subject to height exclusion below)
• partition walls or similar dividing elements
• open circulation areas and entrance halls, corridors and atria

NIA will exclude:

• toilets and associated lobbies (but extra measurements may be required for shops where they are either in excess of normal staff requirements considering the type and size of shop) or it is apparent additional toilets have been installed
• cleaners’ cupboards
• lift rooms, boiler rooms, tank rooms, fuel stores and plant rooms other than those of a trade process nature
• stairwells, lift wells, those parts of entrance halls, atria, landings and balconies used in common or for the purpose of essential access
• corridors and other circulation areas where used in common with other occupiers or of a permanent essential nature
• areas under the control of service or other external authorities
• internal structural walls, walls (whether structural or not) enclosing excluded areas, columns, piers, chimney breasts, other projections, vertical ducts etc
• the space occupied by permanent air conditioning, heating or cooling apparatus and ducting which renders the space substantially unusable having regard to the purpose for which it is intended
• areas with headroom of less than 1.5m (this area should be shown separately but excluded)
• car parking areas (this area should be shown separately and the number of spaces noted)

NIA: common terms

Internal finish

This should be either the brick/blockwork or plaster coat applied to the brick/blockwork, not the surface of internal linings installed by the occupier (generally timber stud frame with a plasterboard, or factory made lining).

Essential access

This will not include reception areas or areas capable of use and situated within entrance halls, atria and landings etc.

Permanent essential nature

Apart from areas used in common with other occupiers, corridors excluded from NIA are those of a permanent essential nature, ie internal corridors between structural walls (usually found in older buildings). Fire corridors and smoke lobbies which are defined by non-structural walls - but only where they are permanent and essential to any prospective tenant of the property and do not merely serve the needs of the actual occupier. If the latter, they should be included.

Structural walls

Walls that are load bearing and essential to the structural stability of the property.

Partition Walls

With one exception partition walls (and any other non-structural elements used to divide accommodation) should be ignored for the purposes of measurement. However, the space on which they stand and any small or awkward areas created (eg corridor) should be included in the NIA. The one exception is where a partition wall defines an excluded area, such as that required for permanent essential access. In those instances NIA should be taken up to the partition wall and the area of the partition should be excluded.

Heights and site area terms

Clear height

The height between the floor surface and the lowest part of the roof trusses, ceiling beams, roof beams or haunches at the eaves.

Internal eaves height

The height between the floor surface and the underside of the roof covering, supporting purlins or underlining (whichever is the lower) at the eaves on the internal wall face.

External eaves height

The height between the ground surface and the exterior of the roof covering at the eaves on the external wall face, ignoring any parapet.

Ceiling height

The height between the floor and the underside of the ceiling. If a false ceiling is installed the ceiling height to the underside of the structural ceiling should also be quoted if possible.

Raised floor height

The clear height between the structural floor surface and the underside of the floor surface or the supporting structure, whichever is the lower.

Site area

The total area of the site within the boundaries, measured in a horizontal plane.

Site depth

The measurement of a site from front to rear boundaries.

Site frontage

The measurement of a site along its frontage between 2 flank boundaries.