The true cost of a window

Full-height glazing sells apartments. This is not in dispute, and any developer who claims otherwise is either lying or losing money. The question is what it costs — not per square metre installed, which is knowable, but across the life of the building, which is rarely calculated.

A triple-glazed unit in a warm climate has roughly four times the heat gain of an insulated opaque wall of the same area, even at good specification. It has perhaps a thirty-year service life against the hundred-year life of the structure behind it. It requires access equipment to clean and, eventually, a crane to replace.

Against that, it delivers daylight and view, both of which are genuine goods with measurable effects on how people feel in a room. The mistake is not glazing. The mistake is uniform glazing — treating the whole envelope as a single condition when a building has north faces and west faces, bedrooms and stairwells, views worth framing and views worth hiding.

At Meridian House the western elevation is 34% glazed and the eastern 61%. At Casa Solana the number is 19% overall, and nobody who has been in those houses describes them as dark. Deep reveals, high sills and a single well-placed opening do more for a room than a wall of glass with a blind permanently drawn across it.

The best window in a building is usually the one you did not also put on the other three sides.