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Saving energy has become a national goal for governments. The thermal regulations (RT) 2005 and 2012 have been developed in this perspective. Overview of this somewhat complex program and insulating materials.

loss of energy in a house

To slow the escape of calories or reduce noise, it is necessary to install an insulating material that will reduce heat loss or noise (sometimes both at the same time). In new construction, the choice of insulation material is wide. In renovation, everything depends on the constraints of the building and the performances that one wishes to achieve.

The puzzle of the rt 2005

Applicable to building permits filed since September 1, 2006, the thermal regulation (RT) 2005 wants to reduce the greenhouse gas emissions (GHG) emitted by buildings. To achieve this goal, consulting firms account for the consumption of heating, ventilation and lighting equipment, as well as the thermal losses of the house (these complex calculations are carried out by software).

The coefficient U

The coefficient U determines the thermal losses (in W / Km2): it represents the average "losses" per square meter of wall or bay window for 1° C of temperature difference between inside and outside.
The lower the U coefficient, the better the performance. To simplify the calculations, the legislator has provided two values: one reference and the other maximum not to exceed ("guardrail").
Any insulating material has characteristics that determine its performance.

Thermal resistance R

The thermal resistance R gives the insulating power of the materials. In principle, it is indicated on the packaging and in the documentation of the manufacturers. R is expressed in m2.K / W. The higher the thermal resistance, the better the insulation.

Thermal conductivity

Thermal conductivity (or lambda,?) Defines the ability of the material to conduct heat. Lambda is equal to the thickness of the material divided by its thermal resistance R (? = Ep / R). The thermal conductivity makes it possible to compare two insulators with equal thickness.
It is expressed in W / m.K. The weaker it is, the better the insulation.

Isolation: silence more

Noise is a preponderant nuisance. Some insulators have thermal and sound characteristics that should not be overlooked when living near a noisy path.

The sound insulation insulation index

The sound insulation insulation index (Rw) represents the capacity of a building element (wall, floor, ceiling, joinery...) to attenuate the intensity of noise, with or without insulation. The higher the index, the better the sound insulation. A 45 dB level is a good performance.

Which insulation to choose?

Insulations are grouped into three broad categories: mineral wools (glass wool or rock wool), synthetic foams and ecological insulation.

Mineral wools

Mineral wools (glass or rock) are very good thermo-acoustic insulators. They come in panels or semi-rigid rolls that are more practical to apply in the attic. Incombustible, they are sensitive to humidity.

Expanded polystyrene

Expanded polystyrene (EPS) is in the form of rigid panels. It is mainly used on walls and floors. It is insensitive to moisture and resists compression. Three versions are marketed: thermal (Th 38), thermal superior (Ultra Th) and thermo-acoustic (Ultra ThA).


Polyurethane (PUR) or extruded polystyrene (PSEX) offer excellent thermal performance. They also have the advantage of being insensitive to moisture. They are used in particular to isolate buried walls, surfaces subjected to heavy loads (tiled floor, external roof, concrete slab...).

Natural insulators

Natural insulation, sheep wool, cotton wool, hemp, wood fibers, cellulose wadding, etc., have performance equivalent to mineral wool. The mode of manufacture and distribution of these products has an impact on their cost. The lack of information on their actual thermal and acoustic performance, fire behavior, even rodents and insects raises many questions.

Thin reflective insulation

Thin Reflective Insulation (IMR) combines air gaps trapped in synthetic materials and at least two infrared reflecting films. According to the standards, their performances are modest: a maximum thermal resistance of 1.35 m2.K / W with a perfect implementation. On the manufacturers' side, the assessment is different: 30 mm of thin insulation is equivalent to 20 cm of mineral wool! In summer, reflective films are effective against overheating in the attic. The table below shows the R values ​​of the insulators for 10 cm thick.

Insulation under the roof

Lost or habitable, the attics require an exem-plaire isolation. In traditional two-layer techniques are added monolayer processes. They provide high performance insulation and simplify implementation. In heavy renovation, the insulating load cells are the best.

In lost roofs, the floors are insulated with rollers or semi-rigid mineral wool panels with vapor barrier. Bulk insulators provide a convenient remedy for attics with difficult access corners.
However, they require a dry and airtight support.

In the habitable attic, we obtain an excellent insulation with mineral wool in rolls of thick laid in a layer on a frame and metal hangers concealed by plasterboard. The technique in two crossed layers is always possible.

In new construction or heavy renovation, when the roof has to be removed, the insulating load-bearing caissons offer continuous high-performance insulation, do not encroach on the living space of the attic and leave exposed the beams of the frame.

On the walls

Wall insulation consists of covering them with a layer of insulation, from the outside or from the inside. This is often the second solution that is adopted in renovation as new, for reasons of cost and simplicity of implementation. Insulation from the outside is not really known and rarely used in detached houses.

On flat walls, we glue doubling complexes (plasterboard + mineral wool, or + PSE, PSEX, PUR).

On stone walls or irregular walls, the technique of the partition wall (insulation + partition plasterboard or gypsum tile...) primarily involves panels of mineral wool. Its flexibility allows it to marry the unevenness of the support and to completely fill the air gap.

The technique of masonry wall partition usually uses mineral wools that perfectly fill the gap between the outer wall and the plaster or cellular concrete tiles.

On a crawl space, the technique of beams and slabs (interjoists) polys-tyrene expanded is the best solution to effectively isolate the floor.

The semi-rigid rockwool panels are easy to manipulate and settle into a metal frame on which the plasterboard is screwed.

The cotton wool has a lambda of 0.036 which allows it to obtain a thermal resistance R = 5.5 in 20 cm of thickness.

Recognizable by their gray color, the Ultra ThA expanded polystyrene lining complexes stand out for their excellent thermo-acoustic insulation.

Insulate floors, above or below

Although it requires less insulation than the other walls of the house, that of the floors of the ground floor on land-full or crawl space remains essential.

The slabs on land-full are insulated with a floating screed: a PSEX or PUR insulation is sandwiched between the existing soil and an insulated concrete screed.

On a crawl space, the insulation of a floor is made with reinforced concrete beams, associated with expanded polystyrene slabs.

The glass wool in rolls are available in thick thickness to obtain, in a single layer, a powerful insulation in the livable attic.

Insulation: the windows too

Windows are also affected by the RT 2005: they represent an important point of thermal losses of the house. The regulation requires to calculate their performances according to four inseparable parameters: the thermal insulation, the solar factor, the surface of the bays and their orientation. The first criterion depends on the manufacture of the product, the others on the bioclimatic design of the building.

Reference thermal insulation level

To match the RT 2005, the windows must have a standard thermal insulation level (Uw or Ujn coefficient) of 1.8 W / m2.K (2.1 W / m2.K in the Mediterranean area).

Note: it is the overall insulation of the joinery that is taken into account in the calculation and not only the double glazing.
Whatever the type of carpentry (wood, PVC or aluminum), the double glazing must be of low emissivity: 4-16-4 ITR indicates a reinforced thermal insulation, that is to say an air space of 16 mm trapped between two panes of 4 mm thick.
One has a film that sends heat back into the house.

For optimal performance, the air gap is replaced by argon, a rare and harmless gas. However, the 2005 RT predicted a guard value of 2.6 W / m2.K, a value that any quality joinery achieves. We will return to the topic of double glazing in a future issue.

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