Buying a house in France: what to watch out for

What does COS, SHON and SHOB mean?

When land or real estate in France is put up for sale, sometimes the advertisement lists one of the above-mentioned terms, but what exactly do they mean?SHOB (Surface hors oeuvre brute) & SHON (Surface hors oeuvre nette) are administrative terms that you will encounter in local land-use plans and planning permits.

The most important document is the PLU (Plan Local d'Urbanisme), which is gradually replacing the older POS (Plan d’Occupation des Sols) document. In the PLU and POS references are made to the COS (Coefficient d’Occupation du Sol). This is a percentage that, when applied to the surface area of the building site, gives the SHON. So when the COS is 10% and the surface area of the land is 2000m², you can build a house of 200m² SHON. If you have French building land for sale, the COS and the thereby derived total surface area are usually indicated. Also for houses that are on sale in France the living surface area is frequently indicated as, for example, 200 m2 SHON.

Calculating the SHON

In order to understand the SHON you should first know what the SHOB is: the sum of the surface areas of each floor, calculated up to the outer edge of the walls. It comprises balconies, corridors, loggias, roof terraces, ceiling spaces, open-air ground floor surfaces, terraces and garages. You then subtract the surfaces that are less than 1.8 meters high from the SHOB. You also subtract the surface areas of the stairs, lifts, unusable ceiling spaces, roof terraces, open-air terraces, balconies, corridors and garages. From this amount you subtract a further 5% for insulation and what remains is the SHON. Compare this version of calculating the SHON with the COS, as described earlier. It’s really very simple.

Living space

Yes, but how do you calculate what is of most importance to you: the “surface habitable”, meaning the actual living space? Let’s use as an example a house with just a ground floor, with a flat roof, rectangular and with outside measurements of 21m x10m. In this case the SHOB is 210m ² (including the flat roof) and there are no factors to be subtracted, except for the insulation, making the SHON 210 x 95% and so 200m². In a modern French house of good quality, the external walls often consist of a 35cm "sandwich" (20 cm for the supporting parts, 10 for the insulation materials and 5 for the inner walls). The inner walls of this hypothetical property are therefore 20.3m & 9,3m, meaning you have an living space of 189m², with a SHON of 200m ². The actual living space will naturally be diminished by the thickness of separating internal walls etc.

From the aforementioned it is evident that there is no fixed relationship between the SHON and the living space. But, a rough rule of thumb is that the living space is approximately 90% of the SHON. By now it will have become clear that in France it is better to employ an architect to request planning permission, if you either want to build something from scratch or if you want to make extensions on an existing house.

A further note on the Superficie Loi Carrez. This law owes its name to the French law which obliges the seller of a property in a “copropriété” (condominium) to state the living surface area in all documents pertaining to the sale. This law generally applies to the sales of apartments, but can also be applied to certain houses built on estates. It contains detailed rules concerning the way in which the living space is calculated, where the most important aspect is the exclusion of every space with a freestanding height of less than 1.8m (just like for the SHON).