Insulate your attic without losing too much space

Insulate your attic without losing too much space

Knowing that 20% of the heat of a house escapes by the roof, it is better to take care of the insulation of its roof spaces. But the insulation causes a loss of surface and volume in the room. So what solutions should you choose to lose as little as possible?

Insulate your attic from the outside

Exterior insulation, when possible, is the ad hoc solution to keep the interior space intact. Admittedly, it costs more than insulation from the inside. But it allows not to touch the interior surface and to keep the ceiling height. A work to be done in fine weather because it requires removing the roof, or even raising the frame with additional rafters in order to be in compliance with the RT (thermal regulations) 2012, whose requirements have been reviewed in the increase: insulation 20% thicker than with RT 2005 in fitted roof spaces, and 30% thicker for lost roof spaces.

Insulation of the attic from the inside

To properly insulate its attic from the inside without losing too much space with the new requirements of the thermal regulations, it is advisable to choose insulators whose lambda (coefficient of thermal insulation) is as low as possible and the R (coefficient resistance) is high. Today we find insulation wools with a lambda of 35 or 32 and a thickness of 26 cm that meet the requirements of RT 2012. But some brands do better. Isover, for example, offers a lambda stone wool of 35 and a thickness of only 10 cm. But before looking for the insulation with the best thickness / insulation ratio, the first thing to do is to seek advice from a professional. Because the type of insulation also depends on the type of your frame.

What about thin insulation?

Opinions on the effectiveness of thin insulation are divided. Thin insulation is a very thin product (from 1.5 cm) made of aluminum layers or aluminized layers. CSTB (Scientific and Technical Center for Building) and Ademe (Environment and Energy Management Agency) recommend using them instead of another insulator.

Roof insulation and tax credit

In 2012, you can benefit from a tax credit of 15% on materials and labor, if however the cost does not exceed € 100 incl. Tax per m² for interior insulation, and € 150 for external insulation. This assistance is capped at € 8,000 for a single person and € 16,000 for a couple, plus € 400 per dependent. As part of a package of work undertaken the same year (work aimed at achieving energy savings), the tax credit climbs to 23%. Finally, note that the insulation work allows you to benefit from the Eco PTZ (eco loan at zero rate), cumulative with the tax credit for the year 2012.


- Thermal regulations are a set of construction rules which aim to limit the primary energy consumption of new buildings. RT 2012 fixes the maximum consumption at 50 kWhEP (m² / year). It applies to all building permits filed since October 28, 2011 for housing located in the ANRU zone, and from January 1, 2013 for other housing. - The lambda coefficient of thermal insulation (λ) is the result of the calculation of the amount of heat that the insulation lets pass in one second on 1m² between the interior and the exterior. - The coefficient R represents the thermal resistance: the higher it is, the more the material is insulating.