The project of the Lelong building in Saint Vincent de Paul consists of the refurbishment and transformation of an old hospital into a residential building with an extension of 4 new levels. The main energy requirement of a residential building in Paris is space heating, which can be offset to a large extent by passive solar heating. The lower levels receive less sun and keep a standard window-to-floor ratio, whereas the upper levels can take full advantage of the sun with a fully transparent double façade system. Winter gardens wrap entirely the building providing a high degree of envelope control: they mitigate heat loss, allow maximum solar gains, daylight and views, reduce infiltration, pre-heat the air for renewal, reduce wind pressure on the façade and provide an enjoyable outdoor space for the summer. In order to determine precisely all these benefits and the actual behaviour of winter gardens, a research project was carried out with Lacaton&Vassal in previous built work.
For this project, the environmental requirements in terms of certification aimed for the PassiveHaus/Enerphit label, the BBCA label and the Bâtiment Biosourcé level 3 label.

"The project is part of the transformation of the Saint-Vincent-de-Paul hospital site. (...) The project aims to renovate the existing but also to densify the site and develop public space to create an urban residential district.
Intentions:
-Housing: Maximum spatial quality for all housing without distinction. Generous spaces to promote appropriation.
-The existing: to do with its qualities, to act in the direction of the existing.
-Environmental approach: Re-use the existing to the maximum of its capacity without destruction. Build efficiently using as little material as possible. A bioclimatic design for the thermal and comfort of the building.
-Landscape: Preserve, repair, consolidate, amplify the vegetation potential already present.
-Involve the inhabitant: Friendly common areas and more generous housing space, to facilitate appropriation."
Lacaton&Vassal

The climate of Paris is temperate with a summer average of 21ºC and peaks reaching 33ºC, and a winter average of 6ºC with peaks reaching -5ºC. In general, the most common source for energy consumption is heating, but special attention needs to be given to the very hot days, as they become more and more frequent. Solar radiation is considerable, with an indirect proportion that is very high. Solar control will be important to regulate heat gains and optimise indoor comfort passively. Prevailing winds come from west-south-west and are not very strong, as the average speed is of 2.5 m/s.