The New Structure Carries Itself: How Lacaton & Vassal Enlarge Social Housing Without Emptying It

Never demolish is a working method, not a slogan

Anne Lacaton and Jean-Philippe Vassal, who won the 2021 Pritzker Prize, are best known for a single line: never demolish, never remove or replace, always add, transform, and reuse. It reads like an environmental slogan, and it is quoted as one. In their practice, though, it functions as a construction sequence — a set of decisions about where the new structure goes, how the old one is touched, and whether the people inside have to leave. The interesting part of Lacaton & Vassal is not that they refuse the wrecking ball on principle. It is that they have worked out, project by project, exactly how to grow a tired building from the outside while it stays occupied.

It began with a greenhouse

The idea is older than the social-housing work. In 1993, for the Latapie House on the edge of Bordeaux, the young practice bolted a cheap agricultural greenhouse onto a modest family home. Transparent, retractable polycarbonate panels formed a winter garden that the family could open to the living room in warm weather and close off in winter, so the usable area of the house expanded and contracted with the seasons. The lesson they drew from it was economic before it was poetic: industrial and agricultural building systems buy enormous volumes of light-filled, weather-protected space for very little money. Generosity, in their vocabulary, is something you can afford once you stop paying for the wrong things.

The move: a structure that carries its own weight

Transferred to a 1960s housing slab, that lesson becomes a precise structural manoeuvre. Rather than stripping and re-cladding the existing facade, Lacaton & Vassal erect an entirely new, self-supporting structure — its own columns on its own new foundations — standing a few metres in front of the old wall. Onto that independent frame they hang prefabricated floor plates, and around it a light envelope of glass and corrugated polycarbonate.

Because the new structure carries itself, it does not load or depend on the ageing building behind it, and that single fact is what lets the old facade be opened up — windows enlarged, walls punched through into the new rooms — without shoring, without structural risk, and crucially without emptying the flats. The residents keep living there. The work happens on the outside and arrives, module by module, already made.

Tour Bois-le-Prêtre: the proof at building scale

The first full-scale demonstration was the Tour Bois-le-Prêtre, a sixteen-storey, hundred-flat tower in northern Paris slated for the usual fate. Working with Frédéric Druot, Lacaton & Vassal added winter gardens and balconies to every apartment in the occupied building. The tower's floor area grew from about 8,900 square metres to 12,460 — the footprint of each dwelling rising by roughly fifteen percent — and the whole transformation came in at 11.25 million euros, around half the cost of demolishing the tower and building new. Nobody was relocated. A resident who had lived for years behind a small window now had a bright, deep room looking over the city, and the public purse had spent less than it would have to lose the housing altogether.

Grand Parc, Bordeaux: sixteen days a flat

The method reached full maturity in the Transformation of 530 Dwellings at Grand Parc in Bordeaux, carried out with Druot and Christophe Hutin and awarded the European Union's Mies van der Rohe prize in 2019. Three occupied 1960s blocks, demolition already ruled out, received the same operation at scale. Each apartment gained twenty-five to thirty square metres of winter garden and balcony — not a token strip, but a genuine second room. Roughly half the entire project budget went into the winter gardens alone.

What makes it repeatable is the speed, and the speed comes from prefabrication. The team could complete an apartment in twelve to sixteen days: about half a day to lay the new concrete slab, two days to adapt the old facade, two days to set the prefabricated winter-garden facade in place, and eight to twelve days for the interior. Throughout, the inhabitants stayed in their homes. The new skin — corrugated polycarbonate and glass in aluminium frames, fitted with reflective solar curtains — went up around lives that never paused.

Why the added layer earns its keep

The winter garden is not merely extra floor. Unheated and glazed, it works as a bioclimatic buffer: it traps solar gain in winter, so the heated rooms behind it sit inside a warmer pocket of air, while its curtains and opening panels shade and ventilate it in summer. The extension therefore improves the building's energy behaviour at the same time as it enlarges it — comfort and lower bills arriving together with the extra square metres, rather than being traded against them.

The claim underneath the glass

The temptation is to read Lacaton & Vassal as a story about a nice material — the cheap greenhouse, the glowing polycarbonate. The sharper reading is structural and social. Their real invention is the decision to add a self-carrying layer in front of a building instead of tearing into it, because that decision is what keeps the residents in place, keeps the embodied carbon of the existing structure in service, and holds the cost at roughly half of starting over. The winter garden is the visible reward. The method is standing just behind it, on its own foundations.