The flat roof is one of the three types of roofs that exist. It differs from other roofs in that it has only one slope. It appears as a terrace with a delicate slope of 2 to 5%. Nowadays, it is more and more used for garages and houses. So, without further ado, let’s dive into this blog and learn some of the important points to consider when choosing a flat roof.

The different types of flat roofs


There are actually two types of flat roofs: the accessible flat roof and the inaccessible flat roof. For the former, users have the ability to use the flat roof. So you can design a living space there by arranging a terrace with a garden. It also offers the possibility of circulating or parking vehicles.

This type of roof is usually covered with wood, stone, concrete, tiles, or earth. For its installation, the ideal is to choose a professional for the installation of roofing. In the case of the second type of roofing, regular use of the surface is not allowed.

This type of roofing is accessible only for maintenance, waterproofing work, and occasional repairs. However, it can accommodate various installations such as flues, vents, etc.

Supporting materials

Because of their very low slope, flat roofs can only accept certain classic materials such as slates and tiles. But it is recommended to protect the waterproofing layers that cover the roofs, whether they are accessible or not. The selection of materials will depend on whether the roof is accessible or not.

In reality, different types of materials are used to support a flat roof. The flat roof is held together by the support that performs the same function as a frame. Three main materials are generally used for the construction of flat roof support. We have masonry (concrete, composite material, or reinforced concrete slab), steel sheet, and wood or its derivatives.

These different materials can be combined to build flat roof support. Also, it is necessary to adapt the material or the combination of materials to the type of dwelling.

Calculating the slope of a flat roof

When we talk about a flat roof, it does not mean that the roof of the building is completely flat. In fact, if you do not design a small slope, rainwater will not be removed. This water will remain on the surface of the roof, which could lead to further damage. It is, therefore, important to apply a slight slope between 1 and 5% in proportion to the surface area. Again, procedures vary depending on the type and size of the roof:

  • Inaccessible flat roofs generally have a slope of about 1%. 
  • Accessible flat roofs or flat roofs have a slope between 1.5% and 2%. 
  • Small flat roofs are generally curved in shape. The middle is the highest point 
  • Large flat roofs have a slight slope. But the slope never exceeds 5%.

In any case, small openings are provided at the bottom of the slope to drain off rainwater. Downspouts are also provided to carry the water to the bottom of the house.

Roof insulation


The insulation of a flat roof is required and indispensable for several reasons. Among other things, it allows:

  • To guarantee thermal comfort in winter and summer.
  • To prevent energy leaks as much as possible.
  • To preserve the support of the flat roof and the structure of the construction in the face of strong temperature changes.

Because of the constant rise in heat, the roof is one of the most sensitive elements of the house.

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