With the amount of materials available, it is not easy to find the best insulation for unused attic space, whether in new builds or renovations. However, unused attic space is often the main source of heat loss in a house. In fact, it is responsible for around 30% of energy loss in a standard home in France. To remedy this problem, thermal insulation of attics is therefore essential, provided that the material chosen has good thermal inertia. Among the most commonly used insulators are glass wool and cellulose insulation.
So what are the main differences between these two materials and which is the best insulation for unused attics?
Glass wool vs. cellulose insulation which is the best insulation for attics?
Glass wool is an insulating material widely used in France in the construction and thermal insulation sectors. It is composed of fine, flexible glass fibers, giving it a texture similar to wool. Glass wool is available in panels, rolls, and loose form. Generally inexpensive, it is applied loose in attics and in panels and rolls in crawl spaces and walls.
cellulose insulation a bio-based thermal insulation material that is becoming increasingly popular, representing a growing market share in the field of attic insulation. Despite some preconceived notions, it now accounts for 20% of attic insulation according to ECIMA. Used for over a century due to its excellent thermal performance, cellulose insulation increasingly cellulose insulation homeowners concerned about the energy efficiency of their homes.
1. Thermal performance:
Density
When blown into attic spaces, glass wool and cellulose insulation the same thermal performance. In fact, to achieve a thermal resistance (R) of 7m2/W.K, the density of glass wool is half that of cellulose insulation less than 4kg/m2 for glass wool compared to more than 8kg/m2 for cellulose insulation. With equivalent thermal performance, the density of cellulose insulation twice that of mineral wool. It is therefore less sensitive to air flow within its fibers.
Thermal conductivity (lambda)
Thermal conductivity is the ability of a material to transmit heat. Expressed as lambda, it provides useful information for evaluating the performance of an insulating material. The lower the lambda value, the less heat the material transmits and the better its insulating performance. The thermal conductivity of blown glass wool in attic spaces is around 0.046 W/(m.K). For cellulose insulation, it is around 0.040 W/(m.K) for the same application.
2. Bulk form:
Glass wool and cellulose insulation available in bulk and can therefore be easily blown into attic spaces. This bulk form allows you to fill all spaces and ensure uniform insulation, even in hard-to-reach areas. It's quick and easy: it only takes a few hours to insulate100m² using a carding and blowing machine. However, glass wool can be irritating when handled, while cellulose insulation be dustier.
3. Hygroscopic properties:
cellulose insulation hygroscopic properties, which means it can absorb, store, and release excess moisture in the ambient air. This gives it an advantage over glass wool. cellulose insulation thus cellulose insulation maintain a good humidity level in attics and prevent condensation problems.
4. Summer comfort and phase shift:
With heat waves in France becoming more frequent, longer, and more intense, summer comfort is an increasingly important concern for homeowners. This is because the materials used in France for roofing (tiles/slates) are relatively thin, allowing heat to easily enter the attic space. As a result, it is not uncommon for the temperature inside the attic to reach twice the outside temperature. In this situation, only insulation with good thermal inertia can slow down the entry of this heat into the house.
cellulose insulation a significant advantage in terms of phase shift. Phase shift is the time it takes for heat to pass through a wall or material. The phase shift of blown glass wool in attic spaces (for a thermal resistanceof R=7m2/W.K) is less than 4 hours, while that of cellulose insulation more than 9 hours. Thanks to its high density and heat storage capacity, cellulose insulation the transfer of heat into the home, providing greater comfort in summer.
5. Energy savings:
Insulating unused attic space helps reduce energy consumption by minimizing heat loss. With a higher density, lower thermal conductivity, and greater phase shift, cellulose insulation offers better thermal performance than glass wool. It helps maintain a more stable indoor temperature, reducing the demand on electrical heating and/or cooling systems.
6. Carbon footprint:
In terms of environmental footprint, cellulose insulation often considered more environmentally friendly than glass wool. cellulose insulation made from recycled materials (selected waste from the paper industry) collected locally by recycling channels. Its manufacture requires neither water nor combustion, as it involves simple mechanical grinding. Salts are added at a rate of 10% to improve its reaction to fire. In addition, thanks to this raw material, cellulose insulation also cellulose insulation biogenic carbon throughout its lifetime (1 ton of cellulose insulation the equivalent of 1.37 tons ofCO2 according to ECIMA's FDES).
The main raw material used in the manufacture of glass wool is silica sand. This sand can come from local quarries or be extracted from specific regions. The manufacture of glass wool has a significant environmental impact, mainly due to the high energy consumption and greenhouse gas emissions involved in the glass melting process: the furnaces used to melt silica sand and other raw materials generally operate at very high temperatures (+1000°C), which requires a large amount of energy. This energy often comes from non-renewable sources, such as fossil fuels, which contributes toCO2 emissions and exacerbates climate change.
So which is the best insulation for unused attic space?
Glass wool and cellulose insulation two popular thermal insulators for insulating unused attic space. While glass wool has long been the most widely used material in France, cellulose insulation market share thanks to its thermal performance and good carbon footprint. In countries accustomed to extreme temperature variations, it is the most widely used thermal insulation material (Finland, Canada, etc.). It also offers hygroscopic properties that help maintain a comfortable humidity level and improve comfort in summer thanks to its high thermal phase shift. Both materials contribute to energy savings in building use, but cellulose insulation for its more favorable carbon footprint, thanks to its production from recycled paper raw materials. This bio-based insulation stores biogenic carbon (CO2) throughout its lifetime, thus helping to meet the new challenges of RE2020.
Reminder of the applicable standard:
In the context of insulating unused attic space, French standard DTU 45.11 is the reference for mineral wool and cellulose insulation. Published in 2020, this standard defines the rules for installation and the performance criteria to be met when installing these loose-fill thermal insulators. Anyone installing these materials for the insulation of unused attic space (whether a professional or a private individual) must comply with these best practices to ensure durable and compliant insulation.
