This article is general information, not legal or professional advice. Energy regulations and aid schemes change quickly and the reforms described below are not yet final. Take advice before buying, renovating or letting.
Last Updated: July 2026
As we write this, 140,000 people have been evacuated ahead of the wildfires burning through the Gironde and the Landes, seven communes on the doorstep of Bordeaux have been emptied as a precaution, and around 3,500 evacuees are sleeping on camp beds in the Bordeaux exhibition centre. France has already counted three heatwaves in June and July 2026, after the earliest May heatwave on record, and forecasters see a fourth building for the final days of the month. Most owners of French property will never face a fire line. The heat, though, comes to every address, and it has exposed an awkward truth about the document that prices every home in the country. In the Paris suburbs, Le Moniteur found a resident whose apartment block was fully renovated by a developer and wears a proud B on its energy certificate. During the late-June canicule his living room hit 36°C. In winter, he says, the heating barely comes on. Nobody had warned him about July. The French have a name for a flat like his: bouilloire thermique, the thermal kettle. The English-language press tends to call it a heat trap. Whatever the name, check for it before you buy or let in France, the same way you would check the roof. Because the DPE letter that governs prices, rental bans and renovation budgets measures winter. Summer lives in a separate indicator that a third of diagnostics do not even display.
What the DPE letter measures, and what it quietly ignores
The diagnostic de performance énergétique grades a home from A to G on two things: its energy consumption and its greenhouse-gas emissions, both of which heating dominates. A flat that sips energy in January earns its A or B whatever happens to it in August, because the letter contains no summer test at all. Since the 2021 reform, the DPE does carry a summer-comfort assessment, the confort d’été indicator described on the ministry’s DPE page and defined in annexe 9 of the arrêté of 31 March 2021. It rates the home’s passive ability to stay cool on a three-level scale, good, medium or insufficient, based on five criteria: external solar protection on south, east and west facing windows, an insulated roof for houses and top-floor flats, the thermal inertia of the walls and floors, whether the layout is traversant (openings on opposite sides for cross-ventilation), and the presence of fixed ceiling fans.
Two design choices make this indicator easy to miss. It has zero influence on the letter, so a B stays a B even when the summer rating is the worst available. And it is displayed as a discreet graphic on page 2 of the report, a smiley where the letter is a billboard. The Fondation pour le logement, the renamed Abbé Pierre foundation, campaigns to make it compulsory on every property listing precisely because almost nobody reads it, and has gone further still, initiating a cross-party bill on heat-trap homes tabled by MPs from eight political groups. The IGNES industry alliance found that a third of DPEs in the national database do not display the indicator at all, along with persistent calculation errors. When you read a French property advert today, you are reading half a thermal report.
One home in two is a heat trap, including the best-rated ones
The numbers come from a study published on 16 June 2026 by Pouget Consultants and IGNES, the alliance of building-electrics industries, which analysed roughly nine million summer-comfort indicators from the ADEME database of DPEs issued since 2021. Only one home in ten achieves a good rating. Nearly one in two is rated insufficient, the study’s working definition of a bouilloire thermique. The headline that should stop an investor mid-scroll: about a third of homes rated A or B, the certificates buyers pay a premium for, are heat traps. Among A-rated homes with an insufficient summer score, 94% simply lack external solar protection, which in plain English means nobody fitted shutters.
Geography compounds the irony, because the homes least adapted to heat sit in the north, built to trap warmth and never asked to shed it. Paris is the extreme case with 67.7% of diagnosed homes rated insufficient, and the Nord and Pas-de-Calais follow at 63.3% and 62.4%. The best-adapted big city is Nice, at 23.2% insufficient, because Mediterranean building culture never abandoned the shutter. New construction offers little comfort either: only 19% of homes built under the RE2020 environmental rules score a good summer rating, and the share does not improve with each regulatory generation. Even the renovation industry looks away, since more than half of regulatory energy audits fail to recommend solar protections for homes that lack them. One honest caveat: the study’s authors note the DPE database is not statistically weighted to the whole housing stock. It is nonetheless the largest dataset that exists on the question, and its direction of travel is not subtle.
Where the heat traps are: a second-home map
The study’s department table reads like a tour of the places our readers buy, so here is the version the property adverts will not show you. The pattern is brutally simple: the further from the Mediterranean, the fewer the shutters, and the higher the share of homes rated insufficient for summer comfort. Brittany and Normandy, beloved of British buyers precisely because they are cooler, hold some of the worst-adapted housing in France, which matters more with every heatwave that now reaches them. The Dordogne sits above the national average. The south coast, for all its heat, is the best prepared, because its builders never stopped assuming the sun would come.
| Département | Insufficient (heat traps) | Good |
|---|---|---|
| Paris | 67.7% | 5.3% |
| Côtes-d’Armor | 63.6% | 6.3% |
| Nord | 63.3% | 6.8% |
| Manche | 61.9% | 4.9% |
| Morbihan | 56.3% | 7.2% |
| Calvados | 54.2% | 8.6% |
| Dordogne | 51.8% | 7.5% |
| Charente-Maritime | 46.7% | 6.2% |
| Gironde | 43.9% | 7.1% |
| Vaucluse | 43.8% | 12.9% |
| Var | 40.1% | 14.8% |
| Hérault | 37.0% | 13.5% |
| Bouches-du-Rhône | 35.3% | 14.3% |
| Alpes-Maritimes | 30.0% | 17.3% |
Among large cities the ranking tells the same story: Nice is the best adapted at 23.2% insufficient, followed by Villeurbanne, Saint-Étienne, Annecy and Tours, while Paris and Lille concentrate heat traps at rates above one home in two. If your investment thesis involves a top-floor Paris pied-à-terre or a Breton cottage for summer lettings, the map is telling you where the due diligence effort belongs.
Why a well-insulated flat cooks: the physics in four sentences
The experts Le Moniteur interviewed are blunt about the cause. French thermal regulations have what the Institut français pour la performance du bâtiment calls a winter DNA: they were written to keep heat in, and around 70% of summer heat enters as solar radiation through glazing, which winter-minded insulation does nothing to stop. Once the heat is inside a tightly insulated shell, it stays, the much-described thermos effect. Renovation can even make August worse in one respect, because insulating walls from the inside cuts the occupants off from the thermal inertia of the masonry, the buffering mass that old churches use to stay cool for days. That inertia explains a paradox our readers know well: the thick-walled stone maison with a mediocre DPE letter that remains blissfully cool through a canicule, while the renovated B-rated flat down the road reaches 36°C.
Materials matter at the margin too: wood-fibre insulation resists heat transfer roughly twice as long as glass wool or polystyrene, a property the trade calls déphasage, the time lag before afternoon heat reaches the interior. But the experts converge on a cheerful conclusion: insulation remains your friend in summer, provided it travels with shade and air. As the IFPEB’s director put it to Le Moniteur, once you have renovated a passoire thermique (a thermal sieve, the F and G homes at the other end of the scale), you are one shutter and one ceiling fan away from not having created a heat trap.
Why this matters to a foreign buyer’s spreadsheet
The DPE letter already moves money. It drives the rental bans that have removed G-rated homes from the market since January 2025, with F to follow in 2028 and E in 2034, and it prices renovation risk into every sale. Our coverage of the Relance Logement bill covers where that framework is heading. The summer indicator moves money more quietly, for now. A furnished letting that turns into an oven collects one-star reviews in the exact weeks it is supposed to earn its yield, and a long-term tenant who spends July at 34°C starts reading up on their rights. Health authorities and courts are increasingly interested in indoor heat, and the government’s own reform direction points one way: summer performance is becoming visible, and what becomes visible gets priced.
All of that cuts in both directions for a buyer. The A-rated new-build studio bought off-plan for furnished letting may be a heat trap nobody flagged, while the old stone house discounted for its E letter may be the most habitable building in the village every August. Neither fact is on the advert. Until the rules change, the buyer who reads page three of the DPE has an information edge over the market, which is not a sentence one gets to write often. And the direction of travel is consistent: the Fondation pour le logement wants the indicator compulsory on every listing, and at least one major city, Lyon, is moving to treat indoor temperature as a criterion of housing salubrity. Every rule in this field has followed the same path over the past five years, first an indicator, then a disclosure duty, then a constraint on letting. Owners of heat traps are early in that timeline, which is exactly when the fixes are cheapest.
The insurance file warms up alongside the thermometer, too. Repeated heat episodes feed the shrink-swell of clay soils that cracks masonry, a peril French home policies treat under the natural-catastrophe regime, and drought raises fire risk around exactly the second-home country now being evacuated in the Gironde. None of that changes who can live in your flat in August, but it is one more reason to reread a French home-insurance contract you may not have opened since completion, and to check what your policy says about climate perils before the next canicule tests both the walls and the paperwork.
Buying the old stone house: the trap inside the renovation quote
Readers hunting a village house meet this collision head on. An E, F or G letter now forces an energy audit at the point of sale, for F and G homes since April 2023 and for E homes since January 2025, and the audit arrives with a scenario of works designed to climb the winter scale. Follow it blindly and you can pay to make August worse. Lining thick stone walls with interior insulation lifts the letter and simultaneously cuts the rooms off from the masonry’s inertia, the one thing keeping the house cool through a canicule. And the audit industry has not yet caught up with the problem, since the IGNES study found more than half of regulatory audits do not recommend solar protections even where the home has none.
The sequencing that preserves both seasons is unglamorous: insulate the roof first, fit external shutters or blinds on the exposed façades, sort the ventilation, and treat the walls last. Where walls must be insulated, exterior insulation keeps the thermal mass on your side of the envelope, and breathable materials like wood fibre buy hours of déphasage that polystyrene does not. None of this is exotic or expensive by French renovation standards, and the new 5.5% VAT and MaPrimeRénov’ eligibility below make the summer items cheaper than they have ever been. The point is to brief your artisan on both seasons, because the quote will otherwise be written for January.
What the government announced: the plan endurance
Three heatwaves concentrate minds. On 17 June 2026 the housing minister, Vincent Jeanbrun, presented a plan named endurance to adapt French homes to heat. The measures that touch owners directly: VAT at 5.5% instead of 20% on external solar protections and on reversible air-to-air heat pumps meeting performance criteria. The heat-pump cut is already in force, since 18 July 2026, ahead of the announced schedule. MaPrimeRénov’, the renovation-aid scheme, now finances external solar protections and ceiling fans within whole-home renovations. Rules for copropriétés are to be eased so that shutters, shading and cooling equipment can be voted through more simply, with a collective loan to finance them. France Rénov’ advisers are to fold summer comfort into renovation guidance, urban cooling networks are slated to double by 2030, and cities are to be greened.
The DPE rebuild: a summer letter is coming
The DPE itself is on the operating table, and not for a polish. After this summer’s heatwaves the minister announced the creation of a dedicated DPE confort d’été, a summer-comfort letter that would sit beside the familiar energy label and tell buyers and tenants how the home holds up in a canicule. Its exact form is still being arbitrated. The first concrete step is narrower and dated: a decree revising the summer-comfort indicator for new homes, promised before 1 January 2027, with a consultation opened this summer on strengthening the indicator across the whole stock. The criteria under discussion read like the checklist later in this article: quality of wall and roof insulation, solar protections, natural ventilation, orientation and materials. The study’s authors want the rewrite to go further and weigh the home’s location and the performance of its equipment, because today the method scores Lille and Marseille as if they shared a climate. They called the June announcements underwhelming, and the pace so far supports them.
Parliament is moving on a second front. The Relance Logement bill, adopted by the Senate at first reading on 8 July 2026, writes summer comfort into the legal definition of a rénovation performante, so a renovation could no longer earn that label while ignoring overheating. The text heads to the Assemblée nationale in the autumn and nothing is final, but the direction matches everything else on this page, and it lands on top of the provisions for landlords we analysed in our guide to the bill’s amortissement for landlords. Add the Fondation’s cross-party heat-trap bill from the previous section and the pattern is hard to miss: three separate legislative vehicles now carry the same idea.
A third reform is running through consultation this very summer on the winter side of the ledger, and it proves that DPE letters move by decree as well as by works. A draft arrêté, open for comment until 6 August 2026, lowers the coefficient converting electricity into primary energy from 1.9 to 1.7 on 1 January 2027. The effect is mechanical: the displayed consumption of electrically heated homes drops by roughly a tenth overnight, and press estimates suggest 300,000 to 500,000 homes would leave passoire status without a single workman crossing the threshold, collecting a free updated attestation from the ADEME observatory. It is the third cut to that coefficient in six years. Gas and oil heating gain nothing, which is the policy’s point.
For an owner, the lesson of all three chantiers is the same. The certificate that prices your property is a regulatory instrument under active reconstruction, in both directions: an electric-heated F may become an E by decree while a sunny B acquires a public heat-trap label. Do not overpay for a letter, and do not over-discount one, without asking what the next arrêté does to it. The smiley is on its way to becoming a headline number. If you own a heat trap, the market will eventually be told.
How to read the DPE you already have
Every DPE since July 2021 contains the summer indicator, whether or not anyone showed it to you. Ask the seller or agent for the full PDF rather than the letter on the advert and look for the confort d’été block, usually a small graphic a few pages in, with its good, medium or insufficient verdict. Then check the inputs behind it, because the IGNES study also found persistent calculation errors and a third of reports not displaying the indicator at all. Each diagnostic carries a reference number, and ADEME’s public observatory of DPEs lets you retrieve the report and see what the diagnostician actually recorded: whether the south-facing windows were noted as protected, whether the roof was treated as insulated, whether the flat was counted as traversant. Five minutes against the reality of the property you visited tells you whether the paperwork describes the building or a hopeful cousin of it.
What we would check before buying (or before July)
Ask for the full DPE report, not the letter on the advert, and find the confort d’été section. If it says insuffisant, or is missing entirely, price accordingly. Then run the five criteria yourself on a viewing, because they cost nothing to check. Which way do the main windows face, and do the south, east and west ones have external shutters or blinds rather than curtains? Is the flat on the top floor, and if so what sits between the ceiling and the sun? Is the layout traversant, or does every opening face the same courtyard? Are the walls stone and concrete, or plasterboard over interior insulation? Visit at 5pm on a hot day if you can. No survey argues with a thermometer.
If you already own the heat trap, the fixes are unglamorous and mostly cheap: external shutters or blinds on the exposed façades, a ceiling fan per bedroom, night ventilation as a habit, and the roof insulated before anything else. The new 5.5% VAT and MaPrimeRénov’ eligibility take the sting out of the invoice. In a copropriété, remember that external shutters usually alter the façade and need the assembly’s authorisation, which is exactly the procedure the plan endurance promises to soften, and check the building’s rules before promising tenants air conditioning. For the wider purchase checklist, our guides to the compromis and promesse de vente and to LMNP furnished letting cover the rest of the paperwork. The DPE was never a lie. It just answers a winter question, and France has started asking a summer one.
FAQ
Does the DPE letter say anything about summer heat?
No. The A-to-G letter reflects energy consumption and emissions, which heating dominates. Summer performance sits in a separate three-level indicator that does not affect the letter and is often overlooked.
What is a bouilloire thermique?
Literally a thermal kettle: in idiomatic English, a heat trap. It is a home that overheats dangerously in summer, typically for want of external shutters, roof insulation or cross-ventilation. The 2026 IGNES and Pouget Consultants study found nearly one diagnosed home in two rated insufficient for summer comfort, including a third of homes rated A or B.
Do the French rental bans depend on summer comfort?
Not today. The bans are keyed to the letter: G since January 2025, F in 2028, E in 2034. The summer indicator has no legal effect on letting yet, but a reform of the indicator is underway and its visibility is set to grow.
Can I add external shutters to a flat in a copropriété?
Usually only with the co-owners’ authorisation, since shutters alter the façade. The government’s plan endurance announced simpler voting rules and a collective loan for exactly this kind of work, so the procedure should ease.
Is air conditioning subsidised in France?
Reversible air-to-air heat pumps meeting performance criteria have carried 5.5% VAT since 18 July 2026, and the plan endurance extends the same rate to external solar protections. MaPrimeRénov’ now covers solar protections and ceiling fans in whole-home renovations. Policy still favours passive cooling first: shade, ventilation and insulation before machinery.
Will the DPE be reformed to reflect summer comfort?
A revision of the summer-comfort indicator for new homes is announced by decree before 1 January 2027, with a consultation on extending a strengthened indicator more widely. Ministerial statements suggest it could become a letter grade of its own, but the final text is not yet published.
