What's the best roof insulation?

Roof insulation plays a major role in keeping the heat in a house. According to ADEME, between 25% and 30% of heat can escape through the roof. This means that properly insulating your roof with materials such as glass wool or rock wool can really improve the thermal comfort of your home.

Flat roofs need special attention as they are more exposed to the elements.

Choosing durable materials is crucial, as insulation has an average lifespan of around 20 years. With financial aids such as MaPrimeRénov and the zero-rate eco-loan available, investing in good roof insulation becomes more accessible.

Not only does this contribute to greater comfort, it also means significant savings on energy bills over time.

Understanding the challenges of roof insulation

Why the roof is the #1 priority for thermal insulation

The roof accounts for up to 30% of heat loss in a house. Insulating the roof is therefore essential to keep the heat in. Good roof insulation increases thermal comfort and reduces heating requirements.

Insulation options include mineral, synthetic and natural materials, each with its own advantages. The quality of installation of the chosen insulation is also crucial to guaranteeing its effectiveness.

By improving roof insulation, you can also increase the property value of your home.

Impact on energy consumption and thermal comfort

Insulating your roof considerably reduces heat loss, with possible savings of 25 to 30% on heating bills. It also improves comfort in the home, summer and winter alike, by maintaining a pleasant indoor temperature.

Insulating materials, especially bio-sourced ones such as cellulose wadding or wood wool, add to thermal well-being while reducing the carbon footprint.

Effective roof insulation makes your home more energy-efficient and comfortable all year round.

It also adds value to your property, making the investment even more worthwhile. Installation must be carried out correctly to exploit the full potential of the insulation chosen, whether in rolls, rigid panels or sprayed.

Interior vs. exterior insulation: what are the differences?

Insulation from the inside is carried out inside the house. This method can reduce the amount of interior space available. It has disadvantages such as thermal bridges.

Conversely, insulation from the outside is applied to the exterior facade. It preserves interior space and avoids thermal bridges, offering better thermal performance.

Exterior insulation can be more expensive. However, the choice between these two methods depends on local regulations and the structure of the house.

💡 Discover our guides to limiting heat loss

Criteria for choosing the right roof insulation

Choosing roof insulation involves considering several criteria. Thermal resistance (R) plays a key role. Good resistance guarantees better insulation.

There are three types of material: mineral, synthetic and natural. Each has its own advantages. For example, rock wool is often appreciated for its performance in attic spaces.

Evaluating the cost and durability of insulation materials is crucial. A well-established budget helps you make the right decision. The ecological footprint must also be taken into account. Finally, the correct installation of insulation has a major influence on its thermal performance.

Careful installation ensures effective, long-lasting insulation.

Thermal resistance (R): what the regulations say

Thermal resistance, or R-value, measures the efficiency of an insulating material. It indicates a material's ability to resist the passage of heat. The higher the value, the better the insulation protects against heat loss.

Regulations impose minimum levels of thermal resistance for roofs. These requirements guarantee good thermal comfort and reduce energy consumption.

When selecting insulation for your roof, always check its thermal resistance. This varies according to the type of insulation, whether mineral, synthetic or bio-sourced.

High-performance insulation, such as glass wool or polyurethane, generally offers a higher R-value. This ensures optimum insulation and long-term savings.

Roof type: lost attic, converted attic, flat roof

Attic space is not easy to fit out. Glass or rock wool is often installed for good insulation. These mineral insulants are effective against cold and damp.

They provide good insulating performance despite limited space.

For converted attics, insulation becomes more technical. Materials such as polyurethane or expanded polystyrene offer excellent thermal conductivity.

They slide easily between the rafters. Homeowners also need to consider waterproofing and soundproofing for optimum comfort.

Flat roofs require special attention. Polyurethane foam panels are often used for their lightness and fire resistance. Installation must be precise to avoid moisture problems.

The right choice of insulation guarantees long-term durability and energy efficiency.

Space constraints, hygrometry, inertia, acoustics, budget

The space available in the roof has a major influence on the choice of insulation. A limited budget can also restrict options.

1. Limited space calls for precise insulation choices. Thermal resistance must match available space constraints.
2. Humidity plays a key role in the choice of insulating materials. Some insulating materials, such as glass wool, can be sensitive to humidity.
3. In certain cases where space is at a premium, complementary solutions can be considered, such as the application of insulating paint. This slightly improves thermal performance without further reducing space.
4. The thermal inertia of materials affects overall comfort inside the home. Mineral insulation materials, such as rock wool, offer good inertia.
5. Sound comfort depends on the acoustic performance of the insulation materials chosen. Choose materials that absorb noise well, for a better indoor environment.
6. Budget serves as a guide when selecting insulating material. It's crucial to include the cost of installation and the durability of the insulation in your budget estimate.
7. Biobased materials may have a higher initial cost, but are often more environmentally friendly in the long term, such as hemp wool or cellulose wadding.
8. Consulting a professional can help you assess these factors according to the specific characteristics of your project. It also ensures compliance with local regulations on thermal and acoustic insulation.

Overview of the main roof insulation families

There are three main types of roof insulation. First, mineral insulations, such as rock wool, dominate the market. They are often considered the best for attics.

Next, synthetic insulations, such as polyurethane and extruded polystyrene, offer good thermal performance in panel form. Finally, biobased insulation, including sheep's wool and absorbent cotton, is gaining in popularity for its reduced environmental impact.

These natural materials fit in well with energy renovation projects.

Thermal resistance is highly dependent on insulation type and climatic conditions. Choosing the right insulation also involves considering thickness and cost. Financial assistance such as MaPrimeRénov is an incentive to carry out such work.

Mineral insulation (glass wool, rock wool)

Glass wool and rock wool are very popular mineral insulants. They offer good value for money and fire resistance. Available in rolls or rigid panels, these materials can be easily adapted to specific roofing requirements.

Rockwool is often considered one of the best choices for attic insulation. These insulating materials are suitable for both interior and exterior roofs.

The thermal performance of mineral insulation depends on the quality of the installation. A good choice of material is essential to guarantee effective insulation. What's more, financial assistance such as MaPrimeRénov is available for work using these materials.

Mineral insulation is therefore a practical and economical solution for the thermal insulation of your roof.

Synthetic insulation (polyurethane, polystyrene)

Synthetic insulation materials such as polyurethane and polystyrene offer many advantages. Polyurethane offers high thermal performance. It's ideal for flat roofs and terraces, thanks to its lightness and resistance to moisture.

On the other hand, the price may be a little high, but its effectiveness justifies the investment. Extruded polystyrene is perfect for green roofs and adapts to irregular shapes.

Polystyrene is economical, with good value for money. It is suitable for both new buildings and renovations. However, its durability may be less than that of polyurethane.

Both materials are eligible for financial assistance such as MaPrimeRénov', making installation more affordable.

Biobased insulation (cellulose wadding, wood wool, hemp)

Cellulose wadding, wood wool and hemp are popular choices for roof insulation. These bio-sourced insulants are environmentally friendly and renewable. They help reduce our carbon footprint.

In summer, their ability to regulate indoor temperature is impressive. In winter, they retain heat efficiently.

These materials also offer good resistance to fire and humidity. Unlike conventional insulating materials, they age well without losing their properties. They ensure optimum thermal comfort all year round.

What's more, thermal resistance varies according to climate and house size. So it's essential to choose the right insulation for a successful project.

Comparing insulation products by use case

To find out which roof insulation is best for which application, we've put together a comparison chart. Here's an overview in HTML :

This table illustrates the choice of insulation suitable for different types of roof. Mineral insulations such as glass and rock wool offer high thermal resistance. Synthetic insulations, such as polyurethane, are ideal for flat roofs. Biobased insulation, such as cellulose wadding and wood wool, are ideal for their low ecological impact and good thermal performance.

For unconverted attic space

Insulating attic space plays a crucial role. It reduces heat loss in your home. Rockwool is a highly effective insulator for this situation.

Its thermal conductivity is between 0.033 and 0.044 W/m.K. This helps maintain a pleasant temperature inside.

Natural insulation materials, such as cellulose wadding, also perform well. They are well suited to an ecologically sound insulation project. Take advantage of financial assistance, such as MaPrimeRénov, to carry out this essential work.

For crawl spaces under roofs (converted attics)

Rockwool and cellulose wadding are high-performance choices for under-roof crawl spaces. Rockwool offers excellent thermal resistance and fire protection.

Its low lambda coefficient guarantees effective insulation. It is also non-combustible and moisture-resistant.

Cellulose wadding is a highly ecological plant-based option. It comes from recycled materials and helps reduce heat loss by 25 to 30%. This insulation provides optimum thermal comfort while respecting the environment.

The two insulating materials ensure a pleasant, well-insulated room.

For flat roofs (terraces, industrial or modern buildings)

Flat roofs require high-performance insulation. Materials such as polyurethane (PUR) and extruded polystyrene (XPS) are effective. They are well suited to terraces and modern buildings.

The right choice of insulation guarantees optimum thermal resistance. This reduces heat loss, especially in winter.

Constraints are also important. The load-bearing capacity of the structure must support the weight of the materials. Accessibility for installation is crucial, especially in industrial areas.

To further improve the energy performance of flat roofs, it can be a good idea to incorporate innovative solutions such as Cool Roof cladding. This coating effectively reflects the sun's heat, significantly reducing the need for air-conditioning.

Adequate ventilation remains essential to prevent damp. Waterproofing systems, such as under-roof screens or membranes, play a key role.

Thermal and acoustic insulation performance

Roof insulation plays a key role in preserving heat. The thermal conductivity of insulation varies from 0.030 to 0.050 W/m.K. This lambda value (λ) indicates the efficiency of each material.

Good thermal resistance depends on the thickness and type of insulation chosen.

For attics, rockwool is the best choice. It offers excellent acoustic insulation. Natural insulation materials, such as cellulose wadding, also help to reduce carbon footprints while protecting against pests.

Opting for the right insulation improves thermal and acoustic comfort in the living space.

Thermal conductivity λ: how to read it

Thermal conductivity, noted λ, measures a material's ability to transmit heat. The lower the λ value, the better the insulation. For example, mineral wool insulation will have a lower λ than polystyrene.

This means it will keep the heat in better.

Thermal phase shift is the time it takes for heat to pass through a material. Greater thickness generally increases phase shift. Using semi-rigid panels or pure foam can improve thermal comfort.

High-performance insulation materials such as sprayed polyurethane help reduce heat loss, while maintaining a good indoor climate.

Thermal phase shifting: choosing the right insulation for your climate

Thermal phase shift is essential for choosing the right insulation for your climate. It determines how long it takes for heat to pass through the insulation. Good insulation delays this passage.

For R = 6 m².K/W, specific thicknesses are required. Rock wool, for example, requires around 28 cm to achieve this resistance. Natural insulation materials such as cellulose wadding also offer interesting performances.

Mineral wools, including glass wool, are renowned for their excellent thermal capacities. They adapt well to different climates and improve thermal comfort in the home.

Choosing the right insulating material means energy savings and a pleasant living environment.

Fire, moisture and pest resistance

Mineral insulation materials, such as rock wool and glass wool, offer excellent safety performance. They are highly resistant to fire and humidity. This is an important factor in ensuring the safety of your home.

Synthetic insulating materials, on the other hand, show varying behavior in the face of fire. Some can ignite easily, posing a potential risk.

Natural insulation materials, such as cellulose wadding, are limited in their resistance to humidity. Poor installation can make these materials sensitive to moisture.

Loose-fill insulation requires special attention. Pests can also be a problem with certain types of insulation, especially those of animal origin. So make sure you choose the right material to guarantee the comfort and safety of your space.

Roof insulation prices

Here's an overview of the costs of different types of roof insulation, a crucial factor in choosing the right material for your project.

These prices vary according to the region, the complexity of the work and the type of roof. They include labor, but may be influenced by other factors, such as the accessibility of the worksite or the specifics of the home. Choosing the right insulation will depend on your budget, your insulation needs and the characteristics of your roof.

Cost per m² depending on material and application

The cost of insulation depends on the material chosen and the installation method. Rock wool costs between €20 and €30 per m², including installation. Polyurethane panels generally cost between €30 and €50 per m².

Biobased insulation materials, such as cellulose wadding, are similarly priced, at around €25 to €40 per m².

For an accurate overview of current prices, you can consult our detailed guide to roof insulation prices per m². This will make it easier for you to estimate your budget by incorporating real market costs.

Choosing slightly more expensive insulation can be more cost-effective in the long term. A good insulator also has to ensure adequate durability. For the work carried out, there are financial aids, such as MaPrimeRénov', which can lighten the budget.

This helps make insulation affordable while guaranteeing optimum thermal comfort.

Total cost with installation for a typical surface

For a house with 100 m² of roof space, the total cost varies according to the type of insulation chosen. For example, for glass wool insulation, the price is around 30 to 50 euros per m², including installation.

Sprayed polyurethane can cost between €70 and €100 per m², as it offers better thermal performance. Biobased insulation such as cellulose wadding can be more affordable, often costing between 50 and 80 euros per m².

The craftsman plays a key role in the final cost. The work can also include elements such as vapour barriers and under-roof screens. For a reasonable budget, it's essential to ask for several quotes and compare options.

Cost vs. long-term performance

Insulation costs vary according to type, but it's essential to evaluate them in terms of durability and long-term performance. Natural insulants, such as cork or wood wool, offer competitive performance while reducing carbon footprints.

Rock wool, often considered the best thermal insulator, delivers excellent long-term performance.

Mineral wools, such as glass wool, offer an attractive cost/performance ratio. Investing in good insulation saves on energy bills.

Financial assistance such as MaPrimeRénov' facilitates this initial investment. They make improving your thermal comfort even more affordable.

Ecology and health: what is the value of "green" insulation?

Green" insulation materials such as cellulose wadding and wood wool offer considerable ecological advantages. These natural materials reduce our carbon footprint. Cellulose wadding, in particular, is ideal for lost attic spaces.

Wood wool, on the other hand, is ideal for converted attics. These options provide effective insulation while protecting the planet.

Using biobased insulation also contributes to healthy living. These materials limit the health risks associated with VOCs, allergens and irritants. What's more, financial assistance is available to encourage the adoption of these sustainable alternatives.

Investing in ecological insulation often generates long-term savings while protecting the environment.

Life cycle analysis and grey energy

Grey energy measures the environmental impact of materials. For insulating materials, it's crucial to examine their lifespan and carbon footprint. Natural insulants, such as flax or cellulose wadding, help reduce this footprint.

They often have a better carbon footprint than synthetic products.

Rockwool, though effective, merits critical analysis. Its life cycle can reveal a significant ecological impact. The thermal conductivity (lambda) of insulating materials also influences their long-term effectiveness.

Choosing sustainable insulation improves the life cycle of materials and reduces grey energy.

Certifications (ACERMI, Ecolabel, natureplus)

ACERMI certification guarantees the performance of thermal roof insulation. When you choose ACERMI-certified insulation, you can be sure of reliable quality. This includes products like wood wool and cellulose wadding, which are biosourced and natural.

The Ecolabel indicates that the insulation complies with strict environmental criteria. PIR panels, for example, are eligible for this certification. The natureplus label also attests to a product's ecological credentials.

These certifications ensure effective thermal insulation while respecting the environment.

Health risks (VOCs, allergens, irritants)

Roof insulation can present health risks. Some insulation materials, such as animal wools, contain chemicals used in their preservation. These products can release Volatile Organic Compounds (VOCs).

VOCs can cause irritation and allergies. Mineral wools, such as rock wool and glass wool, are often considered safer options.

They require no dangerous chemical additives.

It is essential to check the quality of the materials used. Good insulation should limit the release of VOCs and allergens. The use of a vapour barrier can also help control humidity and reduce risks.

Choosing clean, effective insulation helps protect occupants' health. A diagnosis adapted to the type of roof remains crucial to avoid problems linked to pests and damp.

What financial assistance is available for roof insulation?

Insulating your roof can be expensive, but there are a number of financial aids available to reduce this expense. Homeowners can benefit from attractive subsidies.

• MaPrimeRénov' is aimed at owner-occupiers, lessors and condominium associations. This scheme has been strengthened in 2022 to further support insulation work.
• Energy Savings Certificates (CEE) are also available. They enable you to receive bonuses based on the savings achieved through insulation.
• The Eco-prêt à taux zéro (zero-rate eco-loan) offers interest-free financing for energy-related work. This loan makes it easier to carry out ambitious projects such as external or internal insulation.
• In addition to MaPrimeRénov', MaPrimeRénov' also offers a number of "coup de pouce" incentives. These additional incentives encourage the transition to greater energy efficiency.
• A co-rate zero-interest loan (co-PTZ) enables insulation work to be financed without additional interest. This makes the cost more bearable over the long term.
• A free estimate tool lets you find out how much aid is available for your chosen project. This helps to plan finances properly before starting the work.
• Maison Saint-Gobain offers free estimates. The service also helps to find qualified craftsmen to carry out the desired insulation project.

MaPrimeRénov', CEE, TVA réduite, Éco-PTZ

MaPrimeRénov' has been helping households finance their roof insulation work since 2022. MaPrimeRénov' can be combined with Coup de pouce grants and assistance from energy suppliers (CEE).

Households can also benefit from reduced VAT on the work. The zero interest rate co-loan (Eco-PTZ) makes financing even easier.

To benefit from these subsidies, the work must be carried out by an RGE professional. This guarantees the quality of the work. Insulating attics and roofs improves the energy efficiency of homes.

Eligibility conditions by type of work and property

Eligibility conditions depend on the type of dwelling and the work carried out. Assistance is available to owner-occupiers, landlords and even condominium associations.

Roof insulation work must meet specific criteria to qualify. For example, insulation installation must comply with current standards.

MaPrimeRénov' can be combined with Coup de pouce grants and energy company grants (CEE). A professional must guarantee the conformity of the work to ensure eligibility.

The nature of the work also influences access to financial assistance.

Choosing an RGE craftsman: an essential prerequisite

Choosing an RGE (Reconnu Garant de l'Environnement) craftsman is essential. This choice guarantees the quality of the insulation work. Without an RGE professional, it's impossible to benefit from financial aid schemes such as MaPrimeRénov' and Coup de pouce bonuses.

Correct installation of insulation ensures optimum thermal performance. Rock wool, for example, is often considered the best insulation for roofs, especially attic spaces.

Proper installation by a qualified craftsman reduces heat loss, which accounts for 25-30% of a home's total losses. An RGE craftsman is familiar with standards and complies with insulation regulations.

This means you can take full advantage of the benefits of a well-insulated roof.

Conclusion: which solution is best?

To insulate your roof properly, choose the right insulation for your situation. Rockwool and glasswool remain popular options for attics. A preliminary diagnosis is essential to determine the best choice.

Don't neglect the acoustic and thermal aspects of your project. Act now to improve the comfort of your home and reduce your energy bills.

FAQ

1. What's the best insulation for a roof?

Choosing the best insulation for your roof depends on a number of factors, including the type of frame and roofing, and the region where you live. Fiberglass, polyisocyanurate and spray polyurethane insulation are among the most commonly used.

2. How do I choose insulation for my roof?

When choosing insulation for your roof, it's best to call on an expert who can assess your project and suggest the most suitable insulation. He'll take into account the desired thermal resistance, the type of roof structure, and whether or not you have an under-roof membrane.

3. Is thin insulation a good option for a roof?

Thin insulation can be a good option for a roof if you're looking for a quick, low-cost solution. However, it is less resistant than other types of insulation and may not be suitable for all projects.

4. How do I insulate an attic or ceiling?

Different techniques can be used to insulate an attic or ceiling. One of the most common is to use a machine to blow insulation flakes directly onto the attic floor.

5. What is sarking?

Sarking is an external insulation technique that creates a homogeneous layer of insulation over the entire roof surface. It is particularly well suited to exposed roof timbers.

6. What is a vapour barrier and why is it important?

A vapor barrier is a layer of vapor-resistant material installed on the warm side of the insulation to prevent moisture from penetrating the building structure. It is essential to ensure the durability of the insulation.

To find out more :

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