Habitable, Carrez, Boutin: the same flat, three figures
A flat with a conservatory and a low mezzanine can show three different areas, all of them correct.
The answer in three lines
All three start from the same principle: measure the floors, deduct walls, partitions, steps, stairwells, ducts and door reveals, and ignore anything under 1.80 metres of headroom. They diverge on scope and on occasion. The Carrez law is declared when selling a condominium lot and counts enclosed, covered spaces, conservatory included. The habitable area, in the sense of the construction code, additionally excludes conservatories, balconies, cellars, garages and unconverted lofts. The Boutin law is that habitable area, stated in an unfurnished lease.
What sets them apart
Carrez law
Private floor area of a condominium lot. Counts enclosed, covered spaces with at least 1.80 metres of headroom. Does not apply to cellars, garages and parking spaces, nor to lots below eight square metres.
Habitable area
A concept from the construction code. Same deduction of walls and of headroom below 1.80 metres, but additionally excludes conservatories, balconies, loggias, terraces, cellars, basements, garages, sheds and unconverted lofts.
Boutin law
It is not a third calculation method: it is the habitable area, made compulsory in an unfurnished lease. The computation is identical, only the obligation changes.
When to use which
Carrez law
When selling a flat or a condominium lot. It is the area that appears in the preliminary contract and in the deed.
Habitable area
In surveys, planning files and any technical description of the dwelling.
Boutin law
In an unfurnished residential lease. It applies neither to furnished lettings nor to commercial leases.
French rules. An error does not carry the same effect under each text: a Carrez area more than one twentieth below the declared figure entitles the buyer to a price reduction, and a wrong Boutin area exposes the landlord to a rent revision. Check the measurement rather than copying it from a listing.
Frequently asked questions
Why is my Carrez area larger than the Boutin one?
Because the home has a conservatory, an enclosed loggia or another covered space that the habitable area excludes. On the same property, the Carrez area is nearly always greater than or equal to the Boutin one.
Can these areas be computed from a drawing?
Yes for the geometry, provided the drawing is dimensioned and to scale. Two pieces of information remain that the drawing does not always give: the real headroom and whether certain spaces are truly enclosed and covered. Those two points are what you check on site before declaring a figure.
Other common confusions
What if the plan did the work?
FloorScan reads a PDF, produces areas and lengths, and exports in whatever format your counterpart expects.