Purpose / Context - New detached houses have been getting larger in New Zealand for several decades. Large houses require more materials to build, and have greater ongoing energy costs than smaller houses built to the same standard. The purpose of this work was to examine whether larger houses are as efficient at accommodating people as smaller houses. Methodology / Approach - On-line house schematics from major franchise builders in New Zea-land were accessed, and a stratified random sample selected based on dwelling floor-area and de-veloper. These schematics were analysed for number and area of bedrooms (and potential bed-rooms), and number of toilets/bathrooms. Schematics for older social housing were also analysed. The potential occupancy was calculated using several methods. Results – Older social housing had similar potential occupancy to new franchise dwellings of similar size. Larger new franchise dwellings tended to have a lower potential occupancy per square metre than smaller dwellings. Key Findings / Implications – Large houses are built to satisfy current perceived market demands. The ability of the owners to pay for maintenance, and the occupiers to pay for heating/cooling energy will affect both how long the dwelling will last and occupant health. Inefficiencies designed into dwell-ing structure will remain unless there is a major renovation. Large dwellings with high building, running and carbon costs, which are unable to safely and healthily accommodate an appropriate number of people, are unsustainable for society. Originality - This paper provides a critique of the trend of increasing dwelling size.