What thickness for efficient interior wall insulation?

What thickness for efficient interior wall insulation?

Good thermal insulation is essential when it comes to the comfort of a home. However, its effectiveness may vary depending on different criteria. It is therefore important to know which insulation to choose and what thickness to use depending on the type of wall to be insulated.

As energy prices continue to rise, thermal insulation becomes more and more important. Indeed, improving the thermal insulation of a dwelling makes it possible to limit the heat losses by its different walls and thus reduce the heating bill. Thermal insulation also plays an important role with regard to the comfort of accommodation. In fact, a poorly insulated home will cause feelings of cold in winter, despite warm indoor air, and will let in high temperatures in summer. It is for this reason that the RE2020 today imposes insulation criteria, particularly in terms of thickness, from the design dwellings.

interior wall insulation

Why insulate a wall from the inside?

It is therefore important to properly insulate your home. This usually goes through the insulation of the roof, because it is responsible for the majority of heat loss. However, the insulation of interior walls is also essential. Indeed, the walls contribute to the comfort housing. When the latter are cold in winter, they cause a feeling discomfort among residents, despite warm indoor air. Walls are also responsible for 20% to 25% heat loss of a dwelling.

To insulate walls, there are two techniques: external thermal insulation (ITE) and interior thermal insulation (ITI). If ITE is often recommended by professionals because more efficientit is nevertheless more expensive and can be difficult, if not impossible, to achieve. Indeed, there are conditions concerning the condominiumsbut also rules town planning which may hamper its implementation. In addition, this technique is not recommended for old housesbecause it leads to the modification of the exterior facade. Thermal insulation from the inside is therefore an alternative solution more affordable and which entails work of lesser scope. Within the framework of the ITI, the choice of insulation and his thickness are essential criteria. Indeed, the quality insulation but also the preservation of living space depend on it.

What is the best insulation for walls?

How to choose an insulator?

To choose an insulator as part of the insulation of interior walls, there are several performance indicators to consider :

  • The coefficient ofthermal conductivitylambda : it represents the capacity of an insulator to conduct heat, that is to say to let it pass or to insulate it. Thus, the lower this coefficient, the more the material is insulating,
  • thermal resistanceR : it indicates the ability of the insulation to withstand both cold and hot temperatures. It therefore corresponds to the performance of the insulation. The higher the resistance, the better the material performs.

The thermal resistance is particularly related to thickness insulation. Indeed, the higher the resistance, the better the material performs and the thicker the material, the greater the resistance.

The different insulators for interior wall insulation

There are a multitude of thermal insulators of different natures and properties. These are available under different forms (in bulk, in rolls or in the form of thermal insulation plates) and can be classified into several categories depending of materials who make them up:

  • synthetic insulation such as polystyrene or polyurethane: often sold in the form of platesthese insulators are inexpensive and have the advantage of being very insulatingespecially against the cold, while maintaining a thin. On the other hand, they do not bring any improvement in the level of sound insulation and their production process is polluting.
  • Mineral insulation such as glass wool or rock wool: to low costthese insulators are very performing, both thermally and acoustically, and offer a wide range of uses. On the other hand they are less durable and effective against humidity.
  • Natural insulators such as wood wool, hemp, cellulose wadding or cork: sold in bulk or in the form of panels or plates, these insulators are performing but also ecological. They also make it possible to fight against noise and contribute to sound insulation. Nevertheless, this type of insulation is generally more expensive than those mentioned above.

wall insulation thickness

What thickness depending on the insulating material?

Thickness insulation therefore plays an important role with regard to its performancein particular in the context of the insulation of walls from inside. Since resistance and conductivity do not have the same values ​​depending on the insulating materials concerned, the recommended thickness also varies. Indeed, the thermal resistance increases with the thickness of the material, and vice versa. Thus, the more thermal conductivitywhich represents the insulating power of a material, is weak, the more the material is efficient and therefore can be less thick. Polyurethane, for example, has one of the lowest thermal conductivities on the market. This allows him to be high performancewhile maintaining a thin.

The minimum thermal resistance for interior wall insulation is R = 3.7m² K/W. However, this value corresponds to a minimum. It is therefore advisable to aim for a value R = 5 m² K/W in order to guarantee efficiency insulation, but also to anticipate future regulations. Indeed, the environmental regulations regularly revise these thresholds upwards in order to reduce the environmental impact of housing. Organizations that offer financial help for insulation can also attach thresholds to respect in order to benefit from it.

Thus, for a thermal resistance of 3.7 m² K/W, recommended minimum thickness for each material varies:

  • synthetic insulation : between 8 cm for polyurethane in panels and 12 cm for polystyrene,
  • Mineral insulation : between 12 cm for glass wool and 12.5 cm for rock wool,
  • Biosourced insulation : between 14 cm for wood fiber and 15 cm for cellulose wadding.

To insulate the walls from the inside without losing too much space, it is therefore better to favor insulators such as polyurethane or the glass wool.

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