The measure, included in the mammoth Climat et Résilience bill pushed through parliament before the summer break, will apply to houses with F or G ratings on the diagnostic de performance énergétique (DPE) scale.
In most years, around one million homes change hands in France and it is estimated that 13% of these have an F or G DPE rating.
The idea behind the rule is to give buyers a better clue of the costs they will face to improve insulation of the house.
In 2025, the new measure is scheduled to apply to houses with an E rating, and in 2034 to those with a D rating – expected to be a third of all houses on the market.
Meanwhile, from next year landlords with F or G ratings will not be allowed to raise rents, and from 2025 properties with a G rating will not be allowed to be rented out at all.
Where the DPE used to be calculated by looking at energy bills, it is now based on the amount of insulation, the quality of the building and how it is heated.
Around 800,000 homes are expected to fall a grade as a result of the change.