Recommended Method for Determining Building Area
"$2,000 per square metre" — per which square metre? Area is the denominator under every cost rate, benchmark, and efficiency ratio, and one consistent measuring method is what keeps your estimates and comparisons honest. Built on AACE 13S-90.
What "building area" means
It sounds trivial: length × width. But buildings have walls of thickness, shafts, balconies, mezzanines, mechanical rooms, and unfinished spaces — and whether each counts, and where you draw the line, changes the total. Two competent people can measure the "same" building and get areas that differ by 10–20% simply because they used different rules.
Why a standard method matters
Area is the denominator under a huge number of metrics. If the denominator wobbles, every rate built on it wobbles too:
| If area is inconsistent… | …then this breaks |
|---|---|
| Cost-per-area rate ($/m²) | Conceptual estimates are off before you start |
| Benchmark comparisons | You compare projects that were measured differently |
| Efficiency ratios (net ÷ gross) | Design "efficiency" becomes meaningless |
The main area types
You'll meet a family of area definitions. The two you must know cold are gross and net; the rest are refinements:
- Gross area — The total floor area measured to the outer face of exterior walls, including walls, circulation, and shafts. The "whole footprint, every floor."
- Net (usable) area — The actually usable floor space — gross minus walls, structure, shafts, and core. What occupants can really use.
- Circulation & service area — Corridors, stairs, lifts, mechanical and electrical rooms — counted or excluded depending on the metric.
- Special spaces — Balconies, mezzanines, covered-but-unenclosed areas, basements — each needs an explicit rule on whether (and how) it counts.
How to measure consistently
The method matters less than applying one method, consistently, and stating which one you used. A reliable approach:
Nine things to remember
- Building area measurement is a standardized method, not just length × width.
- The same building can have different areas depending on the rules used.
- Area is the denominator under $/m² rates, benchmarks, and efficiency ratios.
- Gross = to outer wall face, including walls and circulation.
- Net = usable space, excluding walls, core, and shafts.
- Special spaces need explicit rules — balconies, mezzanines, basements.
- Net-to-gross ratio measures space efficiency — only valid if measured consistently.
- Compare apples to apples — confirm both rates use the same area definition.
- Always label your number — "gross" or "net," with units. Never a bare figure.
Glossary
- Circulation area
- Corridors, stairs, and lifts serving movement through the building.
- Core
- The central group of shafts, stairs, and services.
- Cost per area ($/m²)
- A cost rate that depends entirely on the area definition.
- Footprint
- The ground-floor outline / area a building covers.
- Gross area
- Floor area to the outer face of exterior walls, all floors.
- Net (usable) area
- The usable floor space, excluding walls, core, and shafts.
- Net-to-gross ratio
- Net ÷ gross — a measure of space efficiency.
- Service area
- Mechanical, electrical, and plumbing spaces.