Thermal sieves in French cities: the rental market under pressure

On a January Tuesday morning in a one-bedroom flat in central Lille, the radiator has been running for hours, yet condensation is still streaming down the bedroom window. The tenant checks the meter before glancing at the cold wall beside the sofa. Elsewhere, the landlord opens the post with a different concern: within a few years, the property may no longer be lettable in its current condition. Similar scenes are playing out in thousands of older buildings, from Paris to Mulhouse and from Roubaix to Saint-Étienne. As the least energy-efficient homes are progressively barred from the rental market, this is no longer a theoretical issue. In some towns and cities, almost one home in four is affected - or could be after a new assessment. France’s map of the problem also holds a few surprises.

Cities where thermal sieves have a major impact on the rental market

Parisian façades may be iconic, but the reality behind them is often less appealing: ageing windows, poorly insulated walls, small attic flats and outdated electric heating. Homes rated F or G, often described as thermal sieves, are especially common in the older housing stock. Lille, Roubaix, Amiens, Nancy, Strasbourg, Lyon, Bordeaux and Saint-Étienne are also among the cities with a high proportion of energy-hungry properties. The figures differ according to the source and the year of the energy performance assessment, but the overall picture is unchanged: in some areas, a share of poorly rated homes close to or above 25 % is far from unusual.

In Lille, narrow townhouses and small blocks built before 1948 account for part of the issue. Data from energy performance assessments show that F and G ratings can make up nearly a quarter of homes in some older neighbourhoods, with considerable differences even between neighbouring streets. In Paris, studios and former maid’s rooms are particularly vulnerable, as their limited floor area can sometimes adversely affect the calculation of the Energy Performance Certificate (EPC). A flat may seem charming during a twenty-minute viewing; in February, when temperatures fall, the experience can quickly feel rather different.

The timetable is now established: G-rated homes have been prohibited from entering the rental market since 1 January 2025, F-rated properties will follow from 2028, and E-rated homes from 2034. This process could remove a meaningful proportion of rental supply in cities dominated by older buildings. A poor EPC does not always reflect every aspect of life in a home, but it already affects its value, its ability to be let and its future. Landlords face the cost of renovation work, while tenants have the very real worry that affordable homes will disappear.

Checks to make before renting or buying

The first step is to request the full EPC, rather than relying solely on the letter displayed in the listing. Check the estimated energy use, greenhouse-gas emissions, heating system, wall insulation and the date of the assessment. An EPC produced before changes to the methodology may sometimes be replaced or amended, particularly for certain small homes. The date genuinely matters. Where available, it is also worth asking for the previous occupants’ energy bills: they do not replace the assessment, but they can offer a more human picture of day-to-day reality.

A common mistake is to be reassured by fresh paint, a new kitchen or an attractive photograph taken in bright sunshine. Those features matter, of course, but they will not warm a poorly insulated bedroom. Realistically, few people check thermal bridges or read the technical appendices to a tenancy agreement every day. Even so, a viewing late in the day - ideally in winter - often reveals a great deal. Feel the walls around the windows, listen for street noise, ask about service charges and look for signs of damp behind furniture.

For a landlord, the answer is not always to rush into renovation work. In a block of flats, external insulation, roof works or collective heating require votes, funding and sometimes several years of planning. For tenants, keeping written correspondence and meter readings may be useful if there is a dispute about the comfort or decency of the property.

“Since 1 January 2025, a home rated G on the EPC can no longer be offered for rent, except in specific circumstances provided for by the regulations.”

• Check the EPC rating and the date on which it was issued;
• Ask which works have already been approved or are planned by the co-ownership;
• Compare the rent with the likely heating costs;
• Check whether the home is subject to a rent freeze.

A map that also reflects the housing crisis

The geography of thermal sieves frequently overlaps with that of high-pressure cities, where finding somewhere to live is already an obstacle course. In Paris, Lille, Lyon and Bordeaux, removing too many properties from the market too quickly could intensify pressure on rents. In Saint-Étienne, Mulhouse and some medium-sized towns, the issue takes a different form: lower purchase prices do not always cover the cost of a full renovation. The balance remains delicate between climate urgency, tenant protection and the actual financial capacity of small landlords. This map identifies more than poorly heated homes; it shows lives dependent on building works, a general-meeting vote or a bank loan.

Key point	Detail	Value for the reader
Most exposed cities	Paris, Lille, Roubaix, Amiens, Lyon, Bordeaux, Strasbourg and Saint-Étienne have large numbers of older homes.	Identify markets where the risk of rental properties being withdrawn is greatest.
Ban timetable	G since 2025, F in 2028, E in 2034, subject to the rules and exemptions in force.	Plan a tenancy, purchase or renovation without waiting until the last moment.
Sensible first step	Read the full EPC, ask about service charges and request details of planned works in the building.	Avoid mistaking an appealing flat for a genuinely comfortable home.