DPE: towards a reform to finally integrate summer comfort

And yet, to this day, summer comfort remains a marginal indicator in the energy assessment of housing.

Despite the increasing frequency of extreme heat waves, summer comfort remains a secondary consideration in the DPE. While it is clearly mentioned, it is not included in the calculation of the rating and remains a mere guideline. This lack of consideration leads to its neglect in sales, rental, or renovation decisions.

For Hello Watt, neglecting summer comfort amounts to missing a central issue in energy diagnosis.

Nearly 80% of French homes for which the summer comfort indicator is provided in the DPE are classified in the “insufficient” and “average” categories, and more than 40% of houses have an insufficient level of summer comfort.

But the reliability of this assessment is called into question:

• software uses imperfect algorithms,
• some accommodations are not evaluated at all on this criterion,
• and the current methodology does not take into account essential parameters such as location or thermal inertia.

After reassessing the indicator, 90% of the housing stock should be classified as “insufficient” or “average” in terms of summer comfort, according to the Pouget Consultants-Ignes study, published in July 2024.

This shortcoming is all the more problematic given that some homes, although well-rated by the DPE for winter, offer poor summer comfort. Buildings with high thermal insulation performance can thus turn into veritable "thermal kettles" in summer due to a lack of effective blackouts, sufficient inertia, or suitable materials.

To address this challenge, Hello Watt offers three options for individuals who wish to improve their summer comfort:

1. Insulate walls and roofs to ensure significant thermal lag (the thermal lag of a material refers to the time it takes for heat to pass through it). Hello Watt's exterior wall insulation solution uses wood wool, a bio-sourced material that guarantees 8 hours of thermal lag, twice as long as expanded polystyrene. For the roof, the company uses Nita-Cotton insulation, with a thermal lag time of 5 hours.
2. Install blackout systems on windows. Hello Watt systematically includes the installation of shutters as part of its window replacement offering.
3. Install a reversible heating system to cool your home in summer: air-to-air heat pumps, also installed by Hello Watt, are ideal for this purpose. Their operation is simple: the outdoor unit captures calories from the outside air, then this energy is transformed and distributed in the form of heat or coolness in the home via the indoor units, through a ventilation system.

For Pierre-François Morin, Director of the energy renovation activity at Hello Watt: "A home can be rated B on the DPE (Energy Performance Certificate) and still become uninhabitable in the summer. This creates a real misunderstanding among individuals, who end up losing trust in the tool. It is urgent to make the DPE more readable, more reliable, and above all more consistent with current climate issues. But beyond this observation, there are already concrete solutions to improve summer comfort: insulating your roof, installing suitable shutters, reinforcing the inertia of the walls, or even opting for a reversible heat pump. These are simple, effective levers that we offer on a daily basis at Hello Watt. Summer comfort should no longer be a secondary criterion in energy renovation."

As the Ministry of Housing prepares to publish initial proposals this summer for changes to the DPE (Energy Performance Certificate), Hello Watt is calling for an ambitious reform based on accurate data, genuine consideration of regional specificities, and enhanced support for households. Adapting housing to extreme heat is no longer simply a matter of comfort, but a public health emergency and an energy imperative.

[1] https://www.lesechos.fr/industrie-services/immobilier-btp/immobilier-le-gouvernement-veut-mieux-tenir-compte-de-la-chaleur-estivale-dans-le-dpe-2162135

Illustrative image of the article via Depositphotos.com.