Attic insulation is one of the most cost-effective energy renovation projects, as heat loss through the roof is often the most significant in a poorly insulated home.
In brief
- Assess the current state of insulation before buying any materials.
- Distinguish between unconverted and converted attics, as the technique differs.
- Plan for a sufficient insulation thickness for a real thermal gain.
- Compare available materials based on budget and acoustic needs.
- Look into available financial support before starting the work.
- Do not neglect ventilation to avoid humidity issues.
Assessing before acting
Before choosing an insulation technique, it is useful to take stock: is there existing insulation, what is its thickness, what is its overall condition. This assessment avoids layering new insulation over an already degraded one, which would limit the overall effectiveness of the work.
Unconverted or converted attics
| Attic type | Common technique |
|---|---|
| Unconverted attic | Blown wool insulation |
| Converted attic | Rigid panels or rolls between rafters |
Unconverted, unoccupied attics are well suited to blown-in insulation, which is quick to install. Converted attics require a more precise technique, usually entrusted to a professional, particularly around roof rafters where available space is more limited.
How much does attic insulation cost
The price depends heavily on the technique and material chosen. For an unconverted attic insulated by blowing, the cost typically falls between 20 and 40 euros per square metre before subsidies, making it the most economical solution. Insulating a converted attic with rigid panels or rolls between rafters generally costs more, between 40 and 75 euros per square metre, due to the greater labour involved and necessary finishing work (vapour barrier, cladding).
These amounts vary by region, surface area to treat and attic accessibility, and should be considered before deducting any available financial support.
Which insulation material to choose
Several materials compete in the attic insulation market, with different performance levels and prices. Glass wool remains the most common, thanks to its affordable cost and ease of installation. Mineral wool additionally offers good acoustic performance and better fire resistance, making it appealing for attics converted into a living space. Cellulose fibre, a bio-based insulator made from recycled paper, appeals for its environmental footprint and its ability to regulate humidity, at a generally somewhat higher price.
The choice depends as much on budget as on priorities: pure thermal performance, acoustic comfort, or the material’s environmental impact.
Choosing the right insulation thickness
Insufficient thickness greatly reduces the effectiveness of the work. For an unconverted attic, aiming for 300 to 400 mm of blown wool achieves a good level of thermal performance, with a direct effect on the home’s energy bill, an effect that can actually be measured by comparing bills before and after the work.
Financial support for attic insulation
Several public schemes can reduce the cost of insulation work, including national renovation grants, energy savings certificates offered by energy suppliers, or a reduced VAT rate for energy renovation work in some countries. Eligibility criteria and amounts change regularly: it is advisable to check the current rules with an official renovation advisory service before starting the project, and to have the work carried out by a certified professional in order to qualify.
Do not forget ventilation
Poorly planned insulation can encourage humidity if ventilation is not maintained. It is essential to keep sufficient air circulation under the roof to avoid any risk of condensation.
Getting professional support for complex cases
For converted attics or a particular roof configuration, calling in a professional remains recommended. This avoids costly mistakes, before tackling other items such as plumbing or electrics as part of a broader renovation project. A renovation broker can help find these professionals and compare their quotes.