A Saturday in late June, third day of a heatwave. Outside, 37°C in the shade. You come home to your apartment — a top-floor two-bedroom bought last year, with a C rating displayed prominently on the certificate, recent windows, an efficient boiler. At 11 pm, the living-room thermometer still reads 32°C. The bedroom under the roof is unusable, you sleep in the living room with the windows open onto a street that never drops below 28°C. Your home performs well in winter — and is unbearable in summer.
This scenario is not a diagnostic anomaly: the A-to-G label of the DPE (Diagnostic de Performance Énergétique — the French Energy Performance Certificate, EPC) measures the dwelling's conventional winter energy performance, not its ability to stay cool during a heatwave. A summer comfort indicator does already appear on every DPE report issued since July 2021 — but it is purely informative, and most buyers and tenants do not even know it exists. By 2028, France's National Climate Change Adaptation Plan intends to turn it into a genuine criterion integrated into the DPE methodology. Here is what changes, which homes are exposed, and how to check where yours stands today.
The DPE label says nothing about your summers: a C-rated home can display an "insufficient" summer comfort level on the very same report. The three-level indicator has existed since the 2021 DPE (decree of 31 March 2021), and the PNACC 3 (March 2025) schedules its overhaul into a reinforced indicator integrated into the methodology by 2028.
What this article covers
What the A-to-G label actually measures — and why it ignores summer heat; the three-level summer comfort indicator present on your DPE since 2021; what the PNACC 3 plans for 2028 (degree-hours methodology, budget, display on property listings); the five physical factors that determine a dwelling's summer comfort; the at-risk property profiles; the works that are effective — and those that MaPrimeRénov' covers poorly.
DPE and summer comfort: what the rules say today — and what they will say in 2028
The A-to-G label measures winter performance, not summer coolness
The DPE label rates the dwelling from A to G according to its conventional primary energy consumption and greenhouse gas emissions, calculated by the 3CL-DPE 2021 methodology (decree of 31 March 2021) across five uses: heating, domestic hot water, cooling, lighting and auxiliaries. Heating overwhelmingly dominates this calculation. As for the cooling item, it is only counted if an air-conditioning system is actually installed in the dwelling: an apartment without air conditioning that climbs to 33°C every summer is not penalised by a single additional kilowatt-hour. The building's ability to stay cool — thermal mass, solar protections, natural ventilation — does not enter the displayed class. A dwelling can therefore be rated C, or even B, and overheat systematically every summer.
The summer comfort indicator already exists — but it is purely informative
Since the DPE reform that entered into force on 1 July 2021, the decree of 31 March 2021 has required every report to include a three-level summer comfort indicator: insufficient, average or good. This indicator is assessed in particular from the building's thermal inertia, the presence of solar protections on the glazed openings, whether the dwelling is dual-aspect (openings on opposite façades), and the presence of fixed ceiling fans. But this level has no influence whatsoever on the A-to-G class: a dwelling rated "insufficient summer comfort" keeps its C label, and no obligation — for letting, for selling, or for renovation — is attached to it. The result: the indicator appears on millions of DPE reports without almost anyone ever reading it.
PNACC 3: a reinforced indicator integrated into the DPE methodology by 2028
The PNACC 3 (Plan national d'adaptation au changement climatique — France's third National Climate Change Adaptation Plan, published in March 2025) changes the game. It provides for the development of a reinforced summer comfort indicator that must complement the DPE methodology by 2028, with a €500,000 budget dedicated to its design. The methodology under consideration relies on degree-hours, inspired by the RE2020 (the French environmental regulation applicable to new buildings): the dwelling's indoor temperature is simulated hour by hour throughout the hot season, and the gaps above a comfort threshold are accumulated over the whole period. Unlike the current indicator, this approach takes the dwelling's location into account — the same apartment does not face the same overheating risk in Lille and in Marseille. An interministerial field study was launched in 2025 to calibrate the method, and displaying the indicator on property listings is under consideration. The ministerial review was announced in spring 2025 by Housing Minister Valérie Létard.
| Milestone | What changes | Text / source |
|---|---|---|
| 1 July 2021 | Three-level summer comfort indicator (insufficient / average / good) on every DPE report — purely informative | Decree of 31 March 2021 |
| March 2025 | Publication of the PNACC 3: reinforced indicator announced, €500,000 budget, degree-hours methodology inspired by the RE2020 | PNACC 3 |
| 2025 | Interministerial calibration field study; ministerial review announced in spring (Valérie Létard) | PNACC 3; Ministry of Housing |
| Horizon 2028 | Reinforced summer comfort indicator complementing the DPE methodology; display on property listings under consideration | PNACC 3 |
A useful point of comparison: in the French overseas territories, this question was settled long ago. The overseas DPE methodology is already adapted to the local climate, and tropical thermal comfort is already at the heart of the overseas DPE. On this front, mainland France will catch up in 2028 with what the overseas departments already practise.
The five physical factors that make (or break) summer comfort
A dwelling's summer behaviour comes down to five physical parameters. The first four already feed the current indicator under the decree of 31 March 2021; the fifth — the roof and the immediate environment — will weigh more in the 2028 methodology, which factors in location. None of these parameters appears in the A-to-G label.
The building's thermal inertia: the mass that dampens the heat
Thermal inertia is the capacity of the walls to absorb heat during the day and release it slowly at night. A Haussmann-era building in dressed stone or a poured-concrete house absorbs a heatwave day with only a few degrees of temperature rise, provided it is properly ventilated at night. Conversely, a lightweight construction — a poorly designed frame, plasterboard partitions, converted attics behind a few centimetres of insulation — heats up within hours and cools down poorly. It is the first parameter assessed by the DPE's summer comfort indicator, and the one over which renovation has the least leverage: you cannot change the mass of an existing building, you compensate with the other four levers.
Solar protections and the orientation of glazed openings
Direct solar radiation through a glazed opening is a dwelling's main heat input in summer. An external protection — shutter, louvre, adjustable sun-breaker — stops this radiation before it passes through the glazing: it is radically more effective than an internal curtain or blind, which lets the heat in and then traps it behind the glass. Orientation worsens or softens the phenomenon: large west-facing windows receive low-angle sun in the late afternoon, precisely when the dwelling has already accumulated the day's heat; south-facing windows are easier to protect with an overhang or a balcony, because the sun sits high there. The summer comfort indicator specifically checks for the presence of solar protections on the glazed openings.
Dual-aspect layout, ceiling fans — and the roof
A dual-aspect dwelling, open on two opposite façades, allows night-time over-ventilation: you open everything wide once the outdoor temperature drops, the draught flushes out the heat stored in the walls, and the cycle can start again the next day. A single-aspect dwelling cannot do this — air does not flow through it, and heat builds up day after day. Fixed ceiling fans, the fourth parameter of the indicator, do not cool the air but markedly improve perceived comfort for a negligible electricity consumption. That leaves the fifth factor, absent from the current indicator yet decisive: the roof and the environment. A top floor under a poorly insulated roof receives direct radiation all day long, and a dwelling located in climate zone H3 (the French Mediterranean rim) or in the heart of an urban heat island no longer benefits from nights cool enough to discharge the building — exactly what the future location-aware degree-hours method will make visible.
What to check on your DPE: the summer comfort indicator appears in the first pages of every DPE report issued since 1 July 2021, as a "confort d'été" (summer comfort) mention with a level — insufficient, average or good — and the characteristics taken into account: building inertia, solar protections on the glazed openings, dual-aspect layout, ceiling fans. Check the displayed level first, then each of the four characteristics: every missing box is an already-identified renovation lever. If your certificate predates July 2021, the indicator is not on it — one more signal that it should be redone.
At-risk homes: when a winter C hides an unbearable summer
Some dwelling profiles concentrate the summer discomfort factors. If you are buying, renting or already own one of the following properties, the summer comfort indicator should weigh as much as the label in your decision.
Profile 1 — Converted attics and top floors under the roof: the roof receives direct solar radiation from morning to evening. Poorly insulated, it turns the room into an oven by the second day of a heatwave, whatever the dwelling's DPE class. It is the most exposed profile in the housing stock.
Profile 2 — Large west- or south-facing windows without external protection: exposed glazed surfaces without shutters or sun-breakers let in a massive heat load. West is the worst orientation: low-angle sun at the end of the day, on a dwelling that is already hot.
Profile 3 — Lightweight, low-inertia construction: light-frame houses, extensions, added storeys and plasterboard partitions heat up fast and store little night-time coolness. Good winter insulation does not correct this defect.
Profile 4 — Single-aspect dwelling: without a second façade there is no through-draught, hence no possible night-time over-ventilation. The heat accumulated during the day is never fully evacuated and the dwelling "charges up" day after day throughout the episode.
Profile 5 — Climate zone H3 and urban heat islands: on the Mediterranean rim and in dense city centres, tropical nights prevent the building from discharging overnight. It is the parameter the current indicator ignores and that the location-aware 2028 methodology will integrate.
Accumulation creates the risk: a studio under the roof, single-aspect and west-facing, in a Mediterranean city centre, stacks four profiles out of five — while still able to display a C label thanks to a recent heating system. It is precisely this gap between the winter class and the summer reality that the reinforced 2028 indicator will make visible on listings.
"Summer" works: effective, but poorly covered by MaPrimeRénov'
The technical solutions for summer comfort are well known, well documented and mostly energy-frugal. Their weak point is not technical: it is financial. MaPrimeRénov' (the French national energy renovation grant) covers summer comfort poorly in mainland France, because the subsidised works are historically geared towards heating performance — and air conditioning is not subsidised at all.
| Works | Effect on summer comfort | Subsidy coverage in mainland France |
|---|---|---|
| External solar protections (shutters, sun-breakers) | Block radiation before the glazing — lever no. 1 on exposed windows | Poorly covered — MaPrimeRénov' works geared towards heating |
| Roof insulation | Cuts the main heat input of top floors; also improves the winter label | Subsidised — as an insulation measure |
| Through-ventilation and night-time over-ventilation | Flushes out at night the heat stored in the walls during the day | Not subsidised as such |
| Fixed ceiling fans | Improve perceived comfort for a negligible consumption | Not subsidised in mainland France |
| Greening (façades, surroundings, shading) | Lowers wall temperatures and the heat-island effect | Not subsidised by MaPrimeRénov' |
| Air conditioning | Cools the interior, but consumes energy and rejects heat outside | Not subsidised — excluded from MaPrimeRénov' |
Only one family of works escapes this blind spot: roof insulation, financed as a "winter" insulation measure, is also the most cost-effective summer measure in homes under the roof. If your budget is tight and your home matches Profile 1, that is where to start. To cost a full package and its impact on your certificate, the OneDpe renovation works simulator lets you test measures item by item.
The market, for its part, is not waiting for 2028. As heatwaves recur, summer comfort is becoming a value criterion in its own right: informed buyers already ask for the indicator during viewings, just like the label. And while the winter calendar keeps tightening — the rental ban on E-rated dwellings arrives in 2034 — summer comfort is establishing itself as the second axis of property valuation.
Key takeaway: the works that will improve the reinforced 2028 indicator are already known today — external solar protections, roof insulation, through-ventilation, ceiling fans, greening. Carrying them out before the reform means acquiring tomorrow's value criterion at today's price.
The four mistakes to avoid on summer comfort
Mistake no. 1 — Buying a top floor without reading the indicator
You visit a bright top-floor apartment in October, C-rated, and you sign without ever opening the "summer comfort" page of the DPE. Yet the information was available: insufficient level, no solar protections, single-aspect dwelling. The first heatwave turns the impulse purchase into a daily problem — and the day the reinforced indicator is displayed on listings, this defect will become visible to all your potential buyers. Before making any offer on an at-risk property (top floor, west-facing windows, zone H3), demand the full DPE report and read the indicator, not just the label.
Mistake no. 2 — Counting on air conditioning
Air conditioning is not subsidised: it is excluded from MaPrimeRénov', and both its installation and its running costs are entirely yours to bear. It treats the symptom without correcting the building — and if the dwelling is a heat sieve (bare roof, unprotected windows), it will run continuously for a mediocre result. Moreover, once installed, its cooling consumption enters the DPE's five uses and can weigh down the displayed conventional consumption. The virtuous logic runs the other way: first reduce the heat inputs (protections, roof), then evacuate (ventilation), and only as a last resort compensate.
Mistake no. 3 — Confusing the label with comfort
"It's a C, so it's a comfortable home": this shortcut is wrong in both directions. The label measures a conventional consumption dominated by heating; it says nothing about summer overheating. A lightweight, single-aspect C can be unbearable in August, while a dual-aspect, high-inertia Haussmann-era E remains liveable without air conditioning. As long as the reinforced indicator is not integrated into the methodology, the two pieces of information — the A-to-G class and the summer comfort level — must be read separately, and both already appear on the report.
Mistake no. 4 — Waiting until 2028 to care
The PNACC 3's 2028 deadline concerns the measuring tool, not the phenomenon: heatwaves are not waiting for the reform. Waiting means enduring several summers of discomfort, paying for the works at tomorrow's prices and risking a discount the day the indicator is displayed on listings. Conversely, the assessed parameters are already known and stable — they are those of the current indicator, complemented by location. Dealing with the subject now means aligning your property with the criterion before it becomes public.
⚠️ Warning: if you buy an at-risk property today (top floor, large west-facing windows, zone H3, single-aspect) without taking summer comfort into account, you expose yourself to a double penalty: real discomfort from the very next heatwave, and a potential discount the day the PNACC 3's reinforced indicator is displayed on property listings.
Check your DPE's summer comfort indicator now
The summer comfort indicator already appears on your DPE — our tool analyses your full certificate, including the parameters that drive this indicator: building inertia, solar protections on the glazed openings, dual-aspect layout, ceiling fans. Enter your DPE number (13 characters, on the first page of the report) to get a detailed analysis of your certificate, spot inconsistencies and identify missing data.
To go further: simulate renovation works and their impact on your home.
Conclusion
The DPE's A-to-G label measures a dwelling's conventional winter performance — it says nothing about its ability to stay cool in a heatwave. The three-level summer comfort indicator, present on every DPE report since July 2021 (decree of 31 March 2021), partially fills that gap, but it remains purely informative. The PNACC 3 of March 2025 schedules its overhaul: a reinforced indicator, calculated in degree-hours on the RE2020 model and taking location into account, will complement the DPE methodology by 2028, with display on property listings under consideration.
At-risk homes — converted attics, unprotected west-facing windows, low inertia, single-aspect layouts, zone H3 — can be identified today, and the effective works are known, even if MaPrimeRénov' covers them poorly in mainland France. Before buying or starting works, the OneDpe DPE verification tool analyses your full certificate, including the parameters that drive your home's summer comfort indicator.
