The choice of thermal insulation for renovating unused attic space depends on several factors, such as budget, desired thermal performance, summer comfort, and other considerations. Here is an overview of the criteria to consider and the different types of insulation commonly used to renovate unused attic space.
Choosing insulation for attic renovation: selection criteria
The budget
One of the main criteria when choosing insulation for renovating an attic is budget. Depending on the size of the attic, the complexity of the preparatory work (whether or not to remove the old insulation, the presence and quantity of heat ducts and recessed lighting fixtures, etc.), and the insulation material chosen, the budget will vary.
It should be noted that rising energy costs have contributed to a sharp increase in the cost of certain materials. Today, cellulose insulation , for example, cellulose insulation the cheapest bio-based insulation for attic spaces, but also the most widely used.
Thermal performance
While approximately 30% of a home's energy loss occurs through the roof, the thermal performance of a material is also crucial in ensuring a stable temperature inside a home.
To measure the thermal performance of a material, several criteria must be taken into account, such as its thermal resistance, conductivity, phase shift, effusivity, diffusivity, hygrothermal properties, damping, etc.
Criteria to consider to ensure comfort in summer >>
Summer comfort
Due to the design of French roofs, the insulation chosen to renovate unused attic space is the only material that provides thermal inertia and slows down the transfer of heat through the roof.
In fact, roofing materials are generally made of brick or slate, which do not provide sufficient inertia. Heat therefore penetrates very easily into the unused attic space of a home. It is not uncommon for the temperature inside to be twice as high as the outside temperature in summer. Once the heat has penetrated the unused attic space, only the ceiling separates it from the interior of the home. Here too, French design does not provide sufficient inertia to block this heat: the ceiling is generally a simple plasterboard panel a few millimeters thick.
In this configuration, only insulation can provide inertia and slow down the entry of heat into the house. Bio-based materials, particularly cellulose insulation very well in terms of summer comfort.
Understanding the importance of attic insulation to ensure comfort in summer >>
Sustainability and stability
Not all materials are equal in terms of longevity. Due to their properties, some materials have a lifespan of more than 50 years, while others will have lost all their performance after 20 years. Houses insulated with cellulose insulation to be demolished in England attest to this 50-year longevity, with no deterioration in the material's performance.
The installation of loose-fill insulation by blowing is susceptible to settling. Insulation sprayed onto a flat surface rather than injected into a closed cavity stabilizes after a few hours. This phenomenon, which is related to the installation technique, is well known, measured, and generally indicated in the ACERMI certification of the material. Professionals therefore apply the quantity necessary for the insulation to achieve the desired performance after settling. Once stabilized, the settling phenomenon does not increase over time.
The shape of the insulation
Several types of materials are used to renovate unused attic space: loose-fill insulation, insulation in rolls, and insulation in panels. Loose-fill insulation such as wood fiber is preferred because it fills even the smallest gaps, thereby limiting thermal bridges. Rolls and panels do not adapt as easily to the surface and can cause air leaks.
What are the advantages of loose-fill insulation? >>
Resistance to moisture and mold
To minimize the risk of moisture and mold in unused attic space, it is essential to install adequate ventilation, ensure airtightness, repair any water leaks, and choose moisture-resistant insulation. In this regard, bio-based materials have hygroscopic properties that make them more resistant to moisture.
For example, cellulose insulation absorb up to 15% of its weight in water, store it, and release it back into the atmosphere when it becomes drier. Its resistance to mold also ensures that the insulation lasts longer.
The environmental impact of insulation
More and more homeowners are concerned about the environmental impact of the products they consume. When renovating, the choice of materials can therefore be influenced by their impact on the environment: conventional materials deplete limited and non-renewable resources (sand, rock) and are very energy-intensive in their manufacturing process (firing in kilns at over 1000°C).
Bio-based materials are derived from natural and renewable resources such as hemp and wood, which can be recycled, such as cellulose insulation paper. Their manufacturing processes are more virtuous and less energy-intensive, which reduces energy consumption and their impact on the environment.
Choosing insulation for attic renovation: the most commonly used materials
Various types of insulation can be used to renovate unused attic space: mineral insulation such as glass wool and rock wool, and bio-based insulation such as cellulose insulation wood fiber. Loose-fill insulation is particularly popular for renovating unused attic space, as it is quick to install and fills gaps effectively.
Glass wool
Glass wool is a commonly used insulation material for thermal renovation of unused attic space due to its availability and relatively low cost.
Although it provides adequate insulation, it has higher thermal conductivity compared to other insulators such as cellulose insulation. This means that, to achieve optimal thermal resistance, a greater thickness of glass wool may be required, which can lead to additional costs.
In addition, the manufacture of glass wool requires significant energy consumption, thereby contributing to the material's environmental footprint. Manufacturing processes often involve the use of recycled glass, but the thermal transformation of sand and recycled glass remains energy-intensive. The greenhouse gas emissions resulting from this production can have an impact on climate change.
Although glass wool can be an affordable option for insulating unused attic space, its relatively modest thermal performance and environmental impact highlight the need to explore other materials that are more energy-efficient and environmentally friendly when renovating homes to improve their thermal performance.
Rock wool
The use of loose rock wool to renovate unused attic space is attracting particular interest due to its exceptional fire-resistant properties. From a fire safety perspective, rock wool stands out for its high fire resistance. Thanks to its non-combustible structure, it offers increased protection against fire risks, making it the preferred choice in applications where fire safety is a priority.
However, this fire safety performance is offset by an unfavorable carbon footprint. The manufacture of rock wool involves energy-intensive processes and the use of raw materials such as basalt and dolomite, thereby contributing significantly to greenhouse gas emissions. The melting and spinning stages required to produce rock wool generate significant emissions, posing challenges in terms of environmental sustainability.
In the current context of growing concerns about climate change, the carbon footprint of rock wool has become a crucial consideration for thermal renovation projects. It is therefore imperative for homeowners and industry professionals to strike a balance between fire safety and environmental sustainability when choosing insulation materials, taking into account the various implications of each option.
Wood fiber
Loose-fill wood fiber is emerging as a preferred option for thermal renovation of unused attic space, offering superior thermal performance. In terms of energy efficiency, wood fiber has excellent insulating properties, with the ability to regulate humidity, absorb CO2, and maintain comfort in summer. Its thermal conductivity is comparable to or even better than that of some conventional insulators such as glass wool, allowing for effective insulation of unused attic spaces without requiring excessive material thickness.
One of the major advantages of wood fiber is its eco-friendly nature. Made from natural wood fibers, often sourced from sustainably managed forests, it has a favorable environmental footprint. The production of wood fiber requires less energy than the manufacture of conventional insulation materials, thereby helping to reduce the carbon footprint associated with thermal renovation. In addition, wood fiber is a renewable and biodegradable material, contributing to environmental sustainability.
However, it is important to note that bulk wood fiber can be more expensive than some alternatives on the market. Its high cost can be a financial barrier for some renovation projects, even though its thermal and environmental benefits are undeniable. Homeowners considering the use of wood fiber will need to carefully evaluate their budget and consider the long-term savings resulting from reduced energy costs.
cellulose insulation
cellulose insulation a popular choice for thermal renovation of unused attic space due to its versatile performance and excellent carbon footprint. It is also the most widely used bio-based insulation in unused attic space (1 in 5 unused attics) according toECIMA.
In terms of thermal performance, cellulose insulation remarkable thermal resistance, providing effective and durable insulation for unused attic spaces. It also has acoustic properties that help reduce noise transmission through the building structure, thereby improving sound comfort inside the home.
One of the notable advantages of cellulose insulation in its hygrothermal properties. By absorbing and releasing moisture depending on ambient conditions, cellulose insulation maintain optimal indoor comfort, thus preventing moisture and condensation problems. This ability to regulate moisture contributes to the durability of the material and the preservation of the building structure.
In terms of its carbon footprint, cellulose insulation favorably. Made from paper fibers, it has a lower carbon footprint than many other insulation materials. Its manufacturing process is energy-efficient (mechanical grinding, dry, without heat) and allows waste from the paper industry to be recycled.
cellulose insulation as a leading option for the thermal renovation of unused attic space, offering remarkable thermal, acoustic, and hygrothermal performance. Its favorable carbon footprint makes it an environmentally friendly choice, responding to growing concerns about sustainability.
Choosing insulation for renovating the attic space of a home depends on various criteria: budget, thermal performance, summer comfort, durability and stability, the shape of the insulation, resistance to moisture and mold, and the environmental impact of the insulation. The most commonly used insulation materials for renovating attics are glass wool, rock wool, cellulose insulation wood fiber. The final choice may also be influenced by more subjective criteria such as the trust placed in the contractor who will carry out the work and their own experience. It is essential to seek expert advice to ensure that the insulation chosen for renovating the attic is suitable for each project.
