Sir,

Simon Curtis, chairman of the RICS Property Measurement Panel, highlights the scope for misunderstandings when seeking to accurately measure floor areas that are 'usable' following the Kilmartin v Safeway case (professional + legal, 22.09.06). As chairman of the 1993 fourth edition of the Code of Measuring Practice, I would like to comment.

When the 1993 edition was produced, it stressed the importance of relying on the three core definitions: gross external area (GEA), gross internal area (GIA), and net internal area (NIA). The current code (fifth edition, 2001) continues the same emphasis. These core definitions do not try to decide what is usable because at the time it was felt that this was not the way to go.

In place of the old definition of sales area in the second (1987) and third (1990) editions, it was decided to omit any reference to usable space in the core special use definitions and instead state the retail area of the shop as the NIA. Only in the ancillary definition of retail storage area does a reference to usable space appear.

The proposal to widen the scope of the usable area test from its limited retail function by applying it to other types of accommodation, such as offices, is probably not appropriate and may result in conflict with the accepted core definition of the NIA.

In 1993, there were debates about what floor area was not included in the NIA. The current definition seems to have stood the test of time. After all, NIA relates to the physical characteristics of the building to be measured.

The danger in applying a user test is a departure from facts and a step into interpretation, where there are always different views. For example, because they exist, corridors are usually categorised as NIA, but whether or not they are usable space is a different matter. It then becomes an issue of valuation, not one of measurement.

Ian Campbell, senior partner, Campbell Gordon