Katraj Market Shelter

A vegetable market had operated on the same patch of ground for over thirty years under a shifting arrangement of tarpaulins and bamboo. The vendors' co-operative wanted a permanent roof. What they asked for was simple and precise: shade, no standing water, and no columns where the produce goes.

The site is a flat rectangle bounded by roads on two sides and a drain on the third, and the market could not close. Any structure had to be buildable in sections around a working market, with the co-operative moving stalls out of the way one strip at a time. That constraint set the entire construction method before the design started.

It is a roof and almost nothing else: eleven steel portal frames at 5.4-metre centres carrying a profiled sheet deck, 5.5 metres to the underside, with a continuous 900mm open ridge for ventilation. Columns land only on the perimeter and on one internal line that follows the existing circulation aisle — the vendors told us where that line was, and we drew it where they said.

The height is the design decision that matters. At 5.5 metres the roof is high enough for hot air to stratify well above head height and escape through the ridge, which is why the space under it sits three to four degrees below the street on a May afternoon. A lower roof would have been considerably cheaper and would have made the market unusable at exactly the times it is busiest. Section AA and the ridge detail on A-501 carry that argument.

Everything is bolted, galvanised and standard. Nothing is welded on site, no section is heavier than two people can carry, and every component is available from three suppliers within a kilometre. The market lost eight trading days in total. Four years on the co-operative has extended it by two bays themselves, using our drawings and no architect, which we consider the best outcome the project could have had.