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How thick should the insulation be for a flat roof in Quebec?




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According to the new Novoclimat standards in effect, the insulation thickness of a flat roof must meet or exceed an R-41 value for new constructions.

However, it may be difficult, if not impossible, to reach this value when renovating existing buildings. You should therefore try to get as close as possible to this value depending on the type of roof and the insulating materials used.

Clinique de la toiture FCA, a roofing company in Montreal, tells you more about it!

Roof insulation and energy efficiency

Did you know that your home could lose up to 30% of its heat if the roof insulation is deficient? And that’s true whether you have a pitched or flat roof!

In fact, a poorly insulated roof will result in significant heat loss. You will notice this, for example, if there are icicles on the edge of the roof or if the snow on your roof melts too quickly.

Hefty electrical bills should also alert you to a possible insulation problem.

Whether you have a residential or a commercial roof, re-insulating your roof will certainly be a good investment since you can easily reduce your energy bill by 25%!

How thick should the insulation on a flat roof be?

The insulation thickness of a flat roof will depend on several factors: the space available, the type of insulation used, the type of building structure, etc. The insulation thickness of a flat roof will depend on several factors.

But before undertaking any insulation work, it is a good idea to seek the help of a roof insulation specialist. They can then inspect the structure of your roof.

Since better insulation causes snow to accumulate instead of melting, it is important to make sure that the roof structure is able to support this additional weight.

The thickness of the roof insulation will depends on the R-value level you wish to achieve; the higher the R-value, the more insulation you will need.

What are the R-value standards for flat roofs?

For buildings constructed before 2012, the value is R-30, while for newer buildings it is R-41.

However, as mentioned earlier, it is sometimes impossible to achieve this figure during renovations, so we try to get as close to it as possible.

The different materials

You can use a variety of materials to insulate your flat roof, including the following:

  • Foam plastic insulation panels

    Whether semi-rigid or rigid, these insulation panels are available in several sizes and thicknesses. Designed for flat walls and roofs, they have a value of R-4 to R-6 per inch of thickness.

  • Blown and sprayed products

    Different types of insulation products can be blown or sprayed on, and have a variable R-value.

    • Cellulose fiber

      Very popular and entirely natural, cellulose fiber can be sprayed or blown. It is made from recycled newspapers and is available at low cost. It has an R-value of approximately 3.7 per inch, so you will need a minimum of 11 inches of insulation thickness to get an R-40 value.

    • Urethane

      Once sprayed, urethane expands and offers a major advantage over panels and fiberglass, since it can fill the gaps and provide optimal insulation. Highly insulating, urethane has an R-value of 7.2 per inch when blown, and R-6 per inch when its long-term effectiveness is considered.

As you can see, the insulation thickness of a flat roof depends on your needs, your budget and the type of material used.

To be sure you are using the right product and to ensure that the insulation thickness of a flat roof is adequate, ask Clinique de la toiture FCA for advice, a re-roofing and roof insulation specialist.

We serve Montreal North, Montreal East, Laval and many other neighbourhood in the Montreal area!



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