How to insulate a flat roof

Written by Posted On Monday, 17 September 2018 09:38

The flat roof is often used in the style of contemporary style homes. This roof model gives a more aesthetic and avant-garde side than a classic tile roof for example. If it is easily accessible and designed for, the flat roof can be considered as an extra floor. It can "dream" in the garden if it is vegetated, on the terrace if you decorate it with outdoor furniture. You can even imagine installing solar panels to partially power your home.

This model roof is not recent; it appeared long ago and these roofs are generally used more for business buildings or residential buildings than for single-family dwellings, although this is becoming more and more common. You will get more information about the flat roof from Strandek.

Insulation and thermal comfort

Appreciated for the numerous possibilities of interior and exterior development that they offer to their occupants, flat roofs are now part of the urban landscape.

As with pitched roofs, their insulation is crucial to ensure true thermal comfort while minimizing energy consumption within the building. The methods of insulation of a flat roof are nevertheless very different from those used for a sloped roof. Here are our explanations in the article below.

1. The insulation methods of the flat roof

Insulation from the outside

Hot roof

In the case of a so-called "hot" roof, the thermal insulation is placed between the waterproofing membrane and the roof support (wood structure, steel tank, concrete slab ...), the latter being covered with a vapor barrier.

Inverted roof

Generally used in the context of a renovation, the inverted roofing method involves the insulation directly on the waterproofing membrane, which is located on the support without a vapor barrier. The insulation is in this case directly in contact with the outside, which requires opting for quality insulation and moisture resistance. Less expensive than the hot roof technical, this type of insulation nevertheless requires that the waterproofing in place be in perfect condition. Easier to execute, it will be a little less effective.

Combined roof

This technique involves applying the existing roofing method to the existing hot roof. Thus, the insulation is placed in two places: the first layer under the waterproofing membrane, the second layer above the same membrane. The roof support and the waterproofing are of consequence and possible impacts caused by falling objects on the roof.

Note however that it is essential that these two layers of insulation are sufficiently thick and that the vapor barrier is powerful to avoid any risk of condensation.

Insulation from the inside

Insulation from the inside, or so-called "cold" flat roof, consists of laying the insulation layer under the roof support, with an air gap between the two. This insulation technique is strongly discouraged due to mold and condensation problems that may develop between the insulation and the substrate. Therefore, it is better to opt for one of the methods described above.

2. Which insulation should I choose for a flat roof?

The chosen material will depend first of all on the method used to insulate the roof. For an inverted roof, for example, prefer extruded polystyrene. If your roof needs to withstand heavy weight on a regular basis (people, vehicles), opt for compression-resistant and sufficiently rigid thermal insulation, such as cellular glass or cork panels. If, on the contrary, it will be accessible only occasionally for its maintenance, the mineral wools will be ideal.

Also, think of the plant as a complementary solution to your insulation! Green roofs protect your roof from rain, wind, sun and temperature variations, thus considerably increasing their lifespan. In addition, the vegetation protects you from the noise and naturally regulates the indoor temperature.

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