Theory 098/Energy & Environment /Building physics
Building Energy Is a Shape Ratio
Energy benchmarks are per square metre of floor. The loss happens at the surface.
Building energy use is set by the ratio of envelope area to volume rather than by floor area, so a compact tall building can use less energy per square metre than a low sprawling one despite more glazing.
01The evidence
Energy intensity varies widely between buildings of similar floor area, and the variation tracks compactness rather than glazing ratio.
02The tension
Benchmarks normalise by floor area, which predicts intensity from size and treats shape as a modifier rather than as the driver.
03The mechanism
Heat loss occurs at the envelope. The ratio of envelope to volume sets how much surface each unit of heated space must maintain, so compact forms lose less per unit volume.
That makes the shape ratio the determinant, and predicts intensity should collapse onto it across building types.
04What this is not
Those normalise by floor area. This normalises by envelope, which explains intensity differences at equal floor area.
05Predictions
- P1Intensity should collapse onto the envelope-to-volume ratio.
- P2Compact buildings should outperform sprawling ones.
- P3Glazing should matter less than shape.
06Refutation
Intensity tracking floor area at controlled shape would restore the benchmark.
07What it changes
It would change building energy ratings.