Measurement of buildings

Cost planning

A typical method of measurement of buildings, as the basis for cost planning, includes the following measurements (as referenced in the National Dictionary of Building and Plumbing Terms):

Fully Enclosed Covered Area (FECA)

This is the sum of all enclosed areas at all building floor levels, including basements (except unexcavated portions), floored roof spaces and attics, garages, penthouses, enclosed porches, attached enclosed covered ways alongside buildings, equipment rooms, lift shafts, vertical ducts, staircases and any other fully enclosed useable areas of the building, measured from the inside face of the external wall. Projections from the face of the wall, such as columns or piers, are ignored. Open (unroofed) courts, light wells and the upper part of rooms, galleries or halls are not included.

Unenclosed Covered Area (UCA)

The sum of all unenclosed areas at all building floor levels, including roofed balconies, open verandahs, porches and porticos, attached open covered ways, undercrofts and useable space under buildings, unenclosed galleries and any other trafficable covered areas of a building which are not totally enclosed by full-height walls. It is measured as the area between enclosing walls or the inside of balustrades. When the covered area is supported by columns, is cantilevered, or is suspended or any combination of these, the measurement is taken to the edge of the paving or to the edge of the covering, which ever is the lesser. The UCA measurement does not include eaves, overhangs, sun-shading devices or awnings unless they relate to clearly defined trafficable covered areas.

Gross Floor Area (GFA)

The total floor area contained within a building, including the horizontal area of external walls. While some commercial and public authorities use variants, the Gross Floor Area is the sum of the FECA and the UCA.

Building Area (BA)

The area of all enclosed and unenclosed spaces at all floor levels of the building to the outside of all enclosing walls, balustrades, columns and the like.

Useable Floor Area (UFA)

The sum of the floor areas measured at floor level from the inside face of the walls of all interior spaces related to the primary function of the building; normally the FECA with the following deductions:

• common-use areas including circulation areas, lobbies and foyers, stairways, lifts, landings, fire escapes, verandahs and balconies, corridors, passages, toilet and restroom areas, cloak and locker rooms, cleaners' rooms, stores and cupboards, and tea rooms or amenity areas
• service areas including mechanical plant rooms, equipment rooms, electrical switchboards or rooms, tank rooms, lift-motor rooms, metre cupboards, telephone cupboards or rooms, garbage areas, loading bays and car-parking areas
• non-habitable areas including the space occupied by columns and structure, internal walls and permanent partitions, lift shafts and service ducts

Area efficiency

This is a measure of the design efficiency, calculated by dividing the Useable Floor Area (UFA) by the Gross Floor Area (GFA) and expressing the result as a percentage.

Site planning

Local councils and other authorities controlling planning have their own set of requirements and definitions for the measurement of buildings. At times, the terminology can be confused with the cost-planning terminology.

Plot ratio

This is a ratio of the Building Area (BA) and the site area expressed as a ratio to 1 (eg 0.5:1 or 1:1). It is not uncommon for planning authorities to describe it as a ratio of the Gross Floor Area and the site area. In this case the planning definition of Gross Floor Area is identical to the NPWC definition of Building Area.

Care should be taken to establish exactly what areas of a building are excluded from the Building Area calculation. Most planning authorities have a list of areas which are not included for their purposes and these exclusions may vary from one authority to the next.

Site cover

In planning terms, site cover is calculated by dividing the footprint area of the building by the site area and expressing the result as a percentage (ie 30% cover or 50% cover).

As in the case of plot ratio, different authorities have differing requirements for the calculation of the footprint area of buildings; some parts of a building are excluded and sometimes unenclosed-covered areas are included. It is important to establish what each authority requires.

Establishing lettable areas

The Property Council of Australia has developed its own set of rules for the measurement of buildings, particularly for establishing lettable areas. Architects involved in services pertaining to leased premises should check these. Rules include definitions for the following:

• Gross Lettable Area – Retail (GLAR)
• Gross Lettable Area (GLA)
• Net Lettable Area Office Buildings (NLA)