Summer comfort: four out of ten homes assessed were deemed insufficient

The increasing frequency of heatwaves has placed summer comfort at the heart of housing renovation challenges. Roof insulation, solar protection, natural ventilation, and building thermal mass are becoming just as crucial as the ability to retain heat in winter.

Published by OneDpe, the 2026 Summer Comfort Barometer is based on the analysis of 11.183.219 energy performance certificates (EPCs) carried out in metropolitan France. EPCs generated from building assessments were excluded from the study.

40,2% of the homes assessed showed insufficient summer comfort

Among the energy performance certificates (EPCs) in which the indicator is included, 40,2% of dwellings are declared "insufficient" in terms of summer comfort. Conversely, 43,2% receive an "average" rating and only 16,6% are considered "good".

These results should, however, be interpreted with caution. The study only covers properties that have undergone an Energy Performance Certificate (EPC) since July 2021 and therefore does not constitute a representative snapshot of the entire French residential housing stock. Furthermore, the summer comfort indicator is not included in 13,6% of the assessments studied.

OneDpe also recalculated the results by strictly applying the criteria set out in Annex 9 of the decree of March 31, 2021. According to this analysis, the proportion of dwellings classified as "insufficient" reached 46,5%. The barometer thus indicates that 16,4% of the recorded assessments were not consistent with the characteristics reported in the energy performance certificate.

An indicator focused on the characteristics of the building

The summer comfort indicator included in the Energy Performance Certificate (EPC) is based primarily on five characteristics of the dwelling:

• the presence of sun protection, such as shutters, blinds or roof overhangs;
• the level of roof insulation;
• the thermal inertia of walls and floors;
• the open-plan design of the dwelling, which facilitates natural ventilation;
• the presence of a fixed air circulator.

This assessment therefore evaluates the building's intrinsic capacity to limit overheating. However, it does not take its location into account. Two dwellings with the same characteristics can thus receive the same assessment, even if one is located in northern France and the other on the Mediterranean coast.

Unlike the energy ratings from A to G, this indicator is purely informational. It does not lead to any rental restrictions and is not linked to the regulatory requirements applicable to energy-inefficient properties.

The North penalized by the current indicator

Based solely on the ratings provided in the DPEs, the municipalities with the highest proportion of housing with insufficient summer comfort are mainly located in Hauts-de-France.

Nine of the ten lowest-rated municipalities are located in the Nord or Pas-de-Calais departments. This situation can be explained in particular by the presence of an old and dense housing stock, composed of dwellings sometimes lacking solar protection, cross ventilation or sufficient roof insulation.

The cooler climate of these areas nevertheless limits their actual exposure to overheating. Conversely, some homes in the south of France may have more favorable architectural features while still being highly exposed due to higher summer temperatures.

Climate and the urban heat island effect are reversing the map

To complement the regulatory indicator, OneDpe has developed a "Summer Score" for homeowners. This score out of 100 combines the building's characteristics, departmental climate data from Météo-France, and the estimated intensity of the urban heat island effect at the address of the dwelling. The lower the score, the greater the potential exposure to discomfort.

When applied to a sample of several million Energy Performance Certificates (EPCs), this method reveals a very different geographical distribution. Among a panel of large cities, Aix-en-Provence obtains a median score of 52 out of 100, Paris 53, and Perpignan 54. Nice and Montpellier each show a score of 58, while their proportion of officially declared "insufficient" housing does not exceed 25%.

Paris is a special case: the capital has a high proportion of poorly adapted housing and a significant urban heat island effect. Building density, the use of concrete and other paved surfaces, and poor nighttime cooling can exacerbate the perceived temperatures in homes.

Renovation work adapted to each situation

The barometer results show that assessing summer comfort cannot be limited to a uniform national approach. The building's location, orientation, immediate surroundings, floor level, and the presence of vegetation must be considered in addition to the data from the Energy Performance Certificate (EPC).

For building professionals, several measures can be taken to limit the risk of overheating. Installing exterior sunshades blocks some of the radiation before it reaches the windows. Roof insulation is also a priority, especially in top-floor apartments or attics.

Cross ventilation, when possible, facilitates heat removal during cooler periods. Ceiling fans can also improve perceived comfort, while the thermal mass of the walls helps slow the temperature rise inside the home.

These solutions, however, must be considered within the framework of a comprehensive assessment. A strategy adapted to a detached house located in a rural community will not necessarily be relevant for an attic apartment situated in the heart of a densely populated metropolis.

Towards a more precise assessment of summer comfort

The OneDpe Barometer reminds us that the third National Climate Change Adaptation Plan plans to evolve the assessment of summer comfort by 2028. A more localized method, capable of taking into account degree-hours of discomfort, must in particular be studied.

Pending potential regulatory changes, the current indicator remains a primary tool for assessing building quality. However, it must be supplemented by an analysis of the local climate, the urban environment, and housing usage patterns.

With the expected intensification of heat waves, summer comfort is becoming a key issue for building inspectors, project owners, landlords, and renovation companies. A home's performance is no longer measured solely by its ability to reduce heating costs; it also depends on its capacity to remain habitable during periods of high temperatures.

Methodology: The barometer is based on Energy Performance Certificates (EPCs) for houses and apartments available in the ADEME open database, excluding certificates generated from building EPCs. The statistics are not weighted and are not representative of the entire residential housing stock. The Summer Score is an indicator developed by OneDpe; it is not a regulatory assessment and does not replace an assessment carried out by a certified professional.