Weighted floor area (surface pondérée)

Two shops of 80 m² do not have the same rental value if one offers 60 m² of sales area at the front and the other 30 m² of sales area and 50 m² of storage in the basement. The surface pondérée (weighted floor area) serves to compare what is not directly comparable. The Charte de l’expertise en évaluation immobilière (the French property valuation charter) defines the principle: reduce the different categories of actual area, according to their usefulness, to a standard area by applying weighting coefficients. The most useful zone (the front sales area, over a limited depth) counts as 1; less useful zones count as a fraction.

Weighting is used first of all for town-centre shops at street level, starting from the gross usable area broken down into zones. The Charte specifies that it may now also be applied to non-commercial areas, and its appendix offers recommendations for dwellings and offices (balconies, terraces, cellars, lofts).

Where the rule comes from

Title III, § 3.5.3 of the Charte (6th edition, November 2025) lays down the principle; chapter 6 details the weighting of commercial areas by category of premises (town-centre shops up to 600 m², medium-sized units, shopping centres, department stores, out-of-town premises); Title V, chapter 1, deals with residential and office areas. The Charte states that the expert may depart from the recommended coefficients provided the choice is justified. Article R. 145-4 of the French Commercial Code requires the residential part of commercial premises to be valued separately where it has an independent access.

In a valuation report

I measure the premises, draw up a zoning plan (frontage, depth, back shop, storage, upper floors, basement, plant rooms) and apply to each zone a coefficient that I justify by the actual configuration: width of the shop window, shape of the premises, access to the upper floors, ceiling height. I present the weighting table in the report, then express the rental value in euros per weighted m² per year, which allows it to be set against rent references in the same street, themselves weighted in the same way. A disagreement on rental value often stems from a difference in weighting: the table makes the discussion possible.

Example

Town-centre shop: 40 m² of sales area at the front over the first five metres of depth (coefficient 1), 30 m² of sales area in the second zone (coefficient 0.5), 20 m² of back shop (coefficient 0.3), 25 m² of storage in the basement (coefficient 0.1). Weighted floor area: 40 + 15 + 6 + 2.5 = 63.5 m² for 115 m² of actual area. With a rental value of €400 per weighted m² per year, taken from recent lettings nearby, the market rent comes to €25,400 a year excluding VAT and service charges.

Not to be confused with

The Carrez floor area is a regulatory private area in co-ownership, without coefficients. The habitable floor area is a regulatory area for dwellings. The GLA (gross leasing area) of shopping centres is a gross contractual area, not weighted.