A comfortable home is not just a matter of decoration or well-chosen furniture. It is primarily a thermal envelope that works, healthy indoor air, and equipment sized for the actual use of the dwelling. Improving one’s habitat involves precise technical choices, often less costly than one might think, provided that the right issues are addressed in the right order.
Summer comfort and regulations: an angle that renovation can no longer ignore
Have you noticed that some rooms become unlivable as soon as the first heat of June arrives? This problem has a technical name: the summer comfort deficiency. The RE2020, which governs new construction, already imposes a dedicated indicator on this subject.
What is changing is that summer comfort is also gaining ground in renovation. Regulatory consultations conducted in 2026 show a gradual tightening of requirements for high-performance energy renovation projects. The summer comfort indicator is now included in a large part of the energy performance certificates (DPE) analyzed in metropolitan France, according to a reuse of open data from ADEME published in August 2026.
In practical terms, protecting your home from summer overheating is no longer a bonus: it is a full-fledged performance criterion. Exterior shutters, air circulators, external attic insulation, or fixed solar protections on south and west-facing windows are the most effective levers. Addressing this issue before installing air conditioning avoids oversizing an energy-hungry system.
Specialized resources like reflexehabitat.com help identify the appropriate work for each housing configuration, from a 1970s bungalow to a poorly oriented recent house.
Thermal insulation and air tightness: where to start the work
The order of renovation work determines their effectiveness. Insulating walls without addressing the roof means losing a significant part of the expected thermal gain. The basic rule remains to start from the top and then go down.
The hierarchy of heat loss in an old home
In an uninsulated house, the roof represents the heaviest loss area, followed by the walls, then the windows and the ground floor. Prioritizing the roof and attic produces the quickest effect on perceived comfort.
Air tightness is the second lever, often overlooked. Unwanted infiltrations (roller shutter boxes, duct passages, wall-floor connections) cool the home in winter and heat it in summer. Before changing windows, checking these points costs little and yields a lot.
Choosing insulation materials according to use
The choice of material depends on the area being treated and the budget. Here are a few guidelines:
- In lost attics, bulk insulators (cellulose wadding, blown rock wool) cover every nook and cranny and limit thermal bridges.
- On walls from the inside, rigid panels (wood fiber, polyurethane) offer a good thickness/performance compromise when space is constrained.
- For ground floors, insulation from below (cellar or crawl space) avoids disturbing the existing floor and reduces the feeling of cold at the feet.
A bio-based material like wood fiber regulates humidity better than a synthetic insulator, which improves indoor air quality without additional ventilation.
DPE and conversion coefficient: what is changing for homeowners
A regulatory change is being prepared for 2027: the conversion coefficient for electricity in the DPE must drop from 1.9 to 1.7, according to the public consultation summary from the ministry published in August 2026. This figure may seem abstract, but its impact is concrete.
Today, a home heated by electricity is penalized in the DPE calculation by this high coefficient. With a reduced coefficient, some homes rated E could shift to D without any work. Certificates of label change are planned for DPEs and audits conducted before this date.
For landlords, this is a point of vigilance. The Climate and Resilience Law gradually prohibits the rental of the least efficient homes. Waiting for the coefficient update before launching an energy audit can avoid financing work on a home whose label will mechanically improve.
Ventilation and indoor air quality: the forgotten aspect of renovation
Insulating a home without adapting its ventilation creates a humidity problem. The more airtight the envelope, the more air renewal must be controlled. A single-flow humidity-controlled mechanical ventilation system is sufficient in most renovated individual homes.
Why this choice? Because it adjusts the extraction flow to the actual humidity level of each room. In a bathroom used twice a day, it runs at a minimum the rest of the time, which limits heat loss.
A double-flow mechanical ventilation system is only justified if the air tightness of the home is very good (test result below 1.0 m³/h/m²). In a partially renovated old home, unwanted leaks cancel out the gains from the heat recovery unit. It is better to invest in air tightness first.
The sizing of extraction vents and air inlets also deserves special attention. Blocked or undersized air inlets create excessive pressure in the home, leading to discomfort (slamming doors, whistling noise) and condensation on cold surfaces.
Improving one’s habitat sustainably relies on a simple logic: address the envelope before the equipment, adapt each intervention to the actual configuration of the home, and follow regulatory developments to determine the right timing. Summer comfort, long considered secondary, has become a performance criterion on par with winter insulation.
