In brief:
- The roof represents up to 30 percent of losses: it is the priority project.
- Externally insulated walls save on average 25 percent on the heating bill.
- MaPrimeRenov’ can cover up to 75 percent of the cost for modest households in 2026.
- An energy audit is mandatory before certain works and is partially funded (up to 500 euros).
Home thermal insulation: the order of priorities
Thermal insulation is the number 1 lever to reduce your energy bill. A poorly insulated house loses on average 30 percent of its heat through the roof, 25 percent through walls, 15 percent through windows and 10 percent through the floor.
Energy audit: the preliminary step
An energy audit carried out by a certified professional identifies weak points and ranks works. It costs between 500 and 1000 euros but is partially funded.
The main insulation areas
Roof: lost or converted attics
Insulating lost attics is the simplest and most profitable. Count between 20 and 50 euros per sqm laid. For converted attics, laying insulation between and under rafters rises to 80 to 150 euros per sqm.
Walls: exterior or interior
| Method | Advantages | Cost per sqm |
|---|---|---|
| Exterior insulation | No loss of surface, better performance | 120 to 200 euros |
| Interior insulation | Cheaper, faster work | 40 to 80 euros |
Choosing the right insulator
“A good insulator is first and foremost a well-installed insulator. Implementation matters more than the chosen material.” — ADEME, Renovation guide 2024
The criteria to look at are lambda (thermal conductivity, the lower the better), thermal resistance R and origin (natural or synthetic).
Financial aid in 2026
- MaPrimeRenov’: up to 75 percent of the cost for modest households
- Energy Savings Certificates (CEE): bonuses paid by suppliers
- Eco-PTZ: zero-interest loan up to 50000 euros
- Reduced VAT at 5.5 percent on installation and materials
Steps to apply for aid
- Get a quote from a certified craftsman
- Submit the aid request BEFORE signing the quote
- Wait for approval notification
- Have the work carried out
- Send invoices for payment
Frequently asked questions
Where to start home thermal insulation?
Start with the roof: it represents up to 30 percent of thermal losses in a poorly insulated home. Then come walls (20 to 25 percent), windows (10 to 15 percent), then the ground floor (7 to 10 percent). This is the most profitable order in terms of return on investment.
What is the best thermal insulator?
There is no universal best insulator: the choice depends on the support, budget and target performance. Glass wool remains the best value for money. Cellulose wadding and wood wool are more ecological. Polyurethane offers the best performance per cm of thickness.
What insulation grants are available in 2026?
MaPrimeRenov’, Energy Savings Certificates (CEE), the eco-PTZ and 5.5 percent reduced VAT remain the main grants in France. A middle-income household can accumulate several thousand euros in aid on a global insulation project.