Small co-owned properties, a "blind spot" in energy renovation, according to a study from the Île-de-France region

Renovating a large complex is "more technically and economically accessible" than carrying out energy performance improvement work in small co-owned properties of fewer than 15 units, explains this study which covers 3,6 million homes in the Ile-de-France region, built before 1991.

These small buildings "are very poorly represented (...) accounting for less than 10% of the projects" for condominium renovation identified through public aid schemes by the IPR, the urban planning agency of Ile-de-France.

The main explanatory factor is the "particularly significant financial effort" in small co-ownerships which are "twice as expensive to renovate (relative to the number of dwellings) and remain a blind spot in the energy renovation market".

Smaller co-ownerships are older: 68% of the co-ownerships with fewer than 20 units analyzed date from before 1945. A characteristic which often implies "less standardized and more complex interventions than the energy renovation of buildings from the Trente Glorieuses".

Energy renovation is therefore more expensive and spread over fewer owners than in a large building.

The study also notes "a lack of companies working on these small co-owned properties", with professionals preferring to work on "more profitable" buildings, "starting at 60 units".

The IPR "notes that small, older condominiums are not only less renovated than buildings from the Trente Glorieuses (the thirty glorious years of post-war economic boom), but also less frequently achieve a good level of energy performance, when they are renovated."

The study includes "one-off" renovations, meaning those where only one type of work is carried out: boiler replacement, wall insulation. These renovations, which result in minimal energy savings, represent 84% of the 70.000 annual renovations recorded between 2021 and 2023.

Overall, it is primarily buildings with "intermediate" energy ratings (C, D, or E) that are being renovated, while energy-inefficient buildings (rated F and G) "remain mostly in the energy-intensive categories E, F, and G." The IPR observes that the more a renovation improves energy performance, the more expensive it is.

As for detached houses in the Île-de-France region, they are more frequently renovated in towns than in rural areas and are "usually done when acquiring" the property, or in case of necessity, such as a disaster or a boiler that needs replacing.

Illustrative image of the article via Depositphotos.com.