Alexander Aronsohn FRICS

Director of Technical International Standards (RICS)

IPMS 1 is used in some markets for planning purposes or the summary costing of development proposals.


IPMS 1 is the sum of the areas of each floor level of a building measured to the outer perimeter of external construction features and reported on a floor-by-floor basis. The definition of IPMS 1 is the same for all classes of building. In many markets, but not universally, this is known as gross external area.

IPMS 1 at a glance

  • It is equivalent to the old measurement of gross external area
  • It is the same for all building classes (office, residential, retail industrial and mixed use)
  • It is used for measuring the area of a building, including external walls
  • It can be used by parties for planning purposes and the summary costings of development proposals
  • IPMS 1 includes and excludes certain areas from the measurement (see below)
  • It also include some measurements, which must be stated separately (balconies, covered galleries, rooftop spaces).


Covered galleries above ground level are deemed to have a notional external wall face consistent with the adjacent wall face of the building. Balconies are measured to their outer face. The external area of basement levels is calculated by extending the exterior plane of the perimeter walls at ground floor level downwards, or by estimation of the wall thickness if the extent of the basement differs from the footprint of the building.


Measurement for IPMS 1 is not to include the area of open light wells or the upper level voids of an atrium, open external stairways which are not an integral part of the structure, for example, an open framework fire escape.

Measurement of IPMS 1 is not to include, but may state separately, if measured, additional areas which are not fully enclosed, such as patios and decks at ground level, external car parking, equipment yards, cooling equipment and refuse areas.


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