Single or Double Layer Insulation?

Between single and double layers, the choice of an insulation solution is most often related to the configuration of the walls of your home and thermal performance.

·        Whether isolated in one or two layers, the only objective is to aim for a high thermal resistance and at least R = 8m².K / W to guarantee the winter and summer comfort as well as the low level of energy consumption requested in BBC construction (primary energy consumption of 50kWh / m2.year on average).

·        How to insulate attic with creepers or attics lost? This is done according to the type of structure and the type of structure, either in a single layer or double layer of insulation.

NB: in multilayer insulation, a single independent and continuous vapor barrier is installed on the heated side of the wall during installation. It acts as both a vapor barrier and an airtight membrane.

Attic insulation in traditional framing

The insulation laid between rafters must have a high thermal resistance given the low availability of thickness (6 to 8 cm). In traditional insulation, the lambda (thermal conductivity) of the insulation used must not be greater than 0.036W / (mK) and the thermal resistance R of the laid thickness must be greater than or equal to 1.65m2.K / W in accordance with the requirements of CPT 3560. In the absence of a HPV (High Water vapor permeability) under-roof screen, the thickness of the insulation installed must allow for an air gap of at least less than 2cm under the face of the battens supports the cover. It must be ventilated from the sewer to the ridge.

The insulation between the rafters does not offer in a single layer of thermal continuity on the whole of the rampant, it does not make it possible to satisfy the levels of thermal resistance corresponding to the regulatory requirements nor to the requirements of comfort. Two layers are therefore necessary to have continuous insulation.

The first layer of bare insulation between rafters must be combined with a second layer between failures. The latter may comprise a kraft coating oriented on the inside (or heated) side. This kraft liner is not a vapor barrier within the meaning of the regulations. The use of insulators must comply with the laying requirements defined in the Application Technical Document (DTA) for the attic insulation specific to each manufacturer

Attic insulation in industrial buildings

The thermal insulation can here be done in a single or double layer, between small houses or under small houses.

Between trusses, semi-rigid panel or roll insulation is inserted without touching the battens or under-roof screen, unless the latter is HPV (High Water Vapor Permeability). The insulation may have a kraft liner on the inside, but the first layer placed between trusses is bare. The second thickness of insulation placed under small trusses makes it possible to limit the thermal bridge induced by these lumber. The lambda of the traditional insulation used is a maximum of 0.036W / (mK). An independent and continuous vapor barrier membrane completes the insulation on the inside. It performs both the role of vapor barrier and airtight membrane (a regulatory measure of air tightness must be carried out at the reception of the building site in new).

Attic insulation lost

The thermal insulation of a lost roof can be achieved by wool to blow. However, depending on the type of floor structure, it can also be done in single or double layer using an insulating panel or roll (wool to unroll).

In floor insulation (wood or concrete), the high insulation thicknesses in rolls available today make it possible to obtain thermal resistances in monolayer up to R = 10m2.K / W. The insulation product must be unwound or placed on the floor, with no gaps or gaps between the floor and the insulation. The different strips must be laid edge to edge and joined together. No fixation is necessary. The insulation must be laid up to the sandpit and reassembled on it being careful not to obstruct the air intakes necessary for the ventilation of the roof when they are in the lower part of the roof (entrances air in low banks).

In insulation on suspended ceiling, two techniques are possible: the insulation by wool unwound or the insulation by wool to blow.

Insulation by wool to unwind:

In the new, a first continuous bed of insulation is placed under the joists to limit the thermal bridge induced by the latter and a second bed is deposited between them to the extent of the overall thermal resistance targeted.

In renovation, a first bed of the height of the joists is deposited between them. It must be of thickness equivalent to the height of the joists. A second bed is unrolled above, perpendicular to the joists and up to the overall target thermal resistance. The insulation should never be straddling the joists with the joist space left empty.