How to correctly calculate your property's floor area?

During a property sale and especially in large cities where every square metre counts, correctly calculating the floor area of a property for sale is essential. This will have a direct influence on the correct sale price to set, serve as a filter for potential buyers, and even have a psychological effect, positive or negative as the case may be, in each of the rooms. To avoid making a mistake, here are the rules that should guide your calculation.

Floor area calculation under the Carrez Law

This legislation has been the reference on this matter since it came into force in June 1997, and sets the standard for calculating floor area according to a very simple rule: any space with a ceiling height of more than 1.80 metres is considered habitable floor space.

However, walls, partitions, ducting, doorways, staircases and stairwells must be deducted from the calculation. Furthermore, certain rooms cannot be taken into account due to their nature; we will return to this later. In rooms with sloping ceilings, you will need to determine which area has a ceiling height exceeding the 1.80 metre standard. The remainder of the room cannot be counted, which is particularly important for bedrooms, which can only be considered as such from 9 square metres.

What is the result used for?

In the case of reselling a property, the aforementioned legislation makes it necessary to have a precise calculation and to state the habitable floor space on the sale documents. This is primarily an obligation for the sale of a property in co-ownership, whether new or old, where an attempt will be made to distinguish the common areas from the private floor area.

In the case of a letting, the lease must also verify that the property is considered decent, i.e., with a floor area exceeding 9 square metres. A tenant discovering that the floor area is less than that advertised may also request a reduction in their rent.

In the case of new-build purchases and off-plan purchases (VEFA), the habitable floor space stated in the contract binds the developer. Likewise, recourse is possible if it ultimately does not appear when the property is delivered.

Finally, the habitable floor space enables the tax authorities to calculate the cadastral rental value, which helps determine the amounts of council tax and domestic rates.

Flexibility for houses

Regarding the sale of a house, the floor area can simply be estimated, unless the property is in horizontal co-ownership, to be clearly distinguished from a housing estate: in co-ownership, the land belongs to the community whereas in a housing estate, it is acquired with the property. In a house, the floor area calculation is primarily used to help the buyer visualise the property when placing the advertisement and during viewings. However, accuracy remains important, even if no supporting documentation is required. A significant difference, subsequently noted by buyers who did not take the precaution of bringing their tape measure during viewings, will not be without consequence!

To protect buyers, a penalty awaits sellers who are poor at mathematics: if the actual floor area is more than 5% less than that stated in the sale agreement, a price reduction may occur. This will then be proportional to the shortfall in square metres. The buyer has one year to take action, which will also result in the solicitor’s fees being recalculated based on the actual sale price. It should be noted that an error in favour of the buyer, however, does not allow the seller to request a price increase.

Beware of rooms excluded from the habitable floor area

An error can notably come from the rooms taken into account in the calculation, as some are excluded from the habitable floor area. If, according to Carrez law, all living rooms, converted attic spaces and solid-built mezzanines should be counted, you should however exclude:

• unfinished cellars and basements, • demountable mezzanines, • terraces and balconies, • common areas, • attics with a ceiling height of less than 1.80 metres, • garages.

Unlike the calculation carried out according to the criteria of the Boutin Law relating to residential letting, workshops, conservatories and loggias can be counted as floor space as defined by Carrez Law under several conditions: they must be entirely private and their ceiling height must exceed 1.80 metres.

It should be noted that storage spaces, such as cupboards, will be counted in terms of floor space, provided their ceiling is more than 1.80 metres high and their floor is at the same level as the rest of the room.

Using a professional?

If you live in co-ownership and are planning to sell, we advise you to enlist the services of a professional surveyor. In addition to the other mandatory certificates, they can carry out the measurement during their visit and provide you with a “Carrez Law certificate” to give to the solicitor.

Nothing prevents you from carrying out the calculation yourself, however you will then take responsibility for the result. The Carrez Law certificate transfers the risk of error to the professional who issued it and protects you from the risk of penalty.

Finally, be aware that it is permanently valid, as long as no alterations modify the room layout or reduce the private floor area.

As you will have understood, whether a habitable floor space certification is mandatory or not, it is best to opt for precision. The calculation rules are complex, which encourages using a professional whose intervention, depending on the location, nature and floor area of the property, may be charged between £60 and £150. If you decide to proceed yourself, you can purchase a laser distance meter at a reasonable cost. It will perform the floor area calculations from the measurements taken, thereby reducing the risk of error.