flat roofMaterials for the frame of a flat roof

When building a flat-roofed house, the choice of materials remains very important. A flat roof timber frame is often used because it is a strong and easy-to-use material.

The choice of roof floor materials can be more complex.

Structural material for flat roof

In the majority of cases, a frame designed for roof terrace is designed using wooden planks (beams), arranged at regular distances and supported by hooves.

We use very often fir, very economical, to design the framework. Other more expensive and expensive wood species can also be used.

There are also metal structures for flat roofs . The use of a metal structure is more rare, but the use of steel beams provides a strong and resistant structure, ideal for a roof terrace. The only drawback is that not all carpenters use metal.

Namely: the roof structure of a flat roof can support up to 200 kg per square meter, which may be essential for some projects.

Materials used for the roof floor

The choice of a frame will depend largely on the material of the floor of the roof. The floor of a roof without slope can be composed of many materials, according to your needs.

An inaccessible flat roof may have a floor consisting of:

  • Steel tray: This is an affordable and useful material for warehouses or industrial buildings. A steel roof flat roof framing has the advantage of not supporting too much weight, and therefore of being inexpensive. But this is not an option for a well insulated building.
  • Concrete: Concrete is a strong and lightweight material, ideal for a flat roof not accessible. It is used perfectly with insulation, and can be adapted for a house with a flat roof.
  • Wood: we can use wood panels for a flat roof. Once again, this builds a light floor. It is an ideal solution to build a home extension . But wood remains a sensitive material, and may require regular treatments.


If you build a roof terrace, on which you intend to circulate, the floor will usually consist of a concrete slab, supported by a solid framework and designed for this purpose. You can either cast a slab or lay a concrete floor.

The different types of flat roofs

The choice of materials for a flat roof and its structure does not depend on your preferences, but rather your project. Each flat roof may require different layouts .

As an indication, note that there are different models of flat roofs, adapted to different needs:

  • Flat Roofing: A flat roof that is not accessible, the main advantage of which is that you can build an attic room under the roof.
  • The green roof (or green roof): a flat roof not accessible covered with substrate and a light layer of vegetation. The greenery offers an aesthetic side and a strong insulating power.
  • The roof terrace: an accessible flat roof that allows you to benefit from an elevated terrace.
  • The roof garden: a green roof that supports plants and shrubs, and can be accessible. What to enjoy a hanging garden in the city.

Keep in mind that the more load-bearing a flat roof has to support, the more expensive and difficult it will be to build . If you are looking for a low-budget home, the flat roof will be much less expensive than a roof terrace, itself less expensive than a roof garden.

Our advice: to have a precise idea of ​​the budget to provide, the ideal is to request quotes for roof terrace to specialized builders. Our site allows you to receive free and no obligation quotes from companies close to you.

The structure of a flat roof

It seems important to note that the roof terrace is a complete structure that meets strict standards . We can not conceive its structure without knowing precisely the loads supported and the exact nature of the future roof.

As a general rule, a flat roof will consist of the following, from top to bottom:

  • The framework, which supports the loads and is integrated into a reinforced concrete structure,
  • The floor support, which allows to spread the following elements,
  • A vapor barrier or waterproofing membrane, which guarantees the waterproofness of the roof,
  • A layer of insulation, which ensures the thermal and sound insulation of the roof,
  • A roof finish, which protects the insulation, serves as a support and can allow circulation.

In the case of a green roof, a drainage layer, filters and a substrate capable of accommodating the vegetation must also be integrated.

Can we build the frame of a roof terrace?

You will understand, reading this article, that the construction of a flat roof is particularly technical . This type of task requires many precautions and involves major technical constraints, in particular to ensure:

  • The waterproofness of the flat roof,
  • The flow of water,
  • The insulation of the roof,
  • The support of the loads.

As a result, we advise you to entrust your flat roof framing to certified professionals . Trust only reputable carpenters who are used to working on flat roofs.

Our opinion: the only cases where self-construction is possible are for the construction of a secondary building (type garden shed), which does not require insulation and must not withstand heavy loads.

Price of a flat roof structure

Finally, let’s go back quickly to the flat roof construction rates. As we have seen, the cost of a flat roof structure depends directly on the nature of the structure.

Since all the elements of the roof are designed together, it is rare to entrust only the frame to a craftsman. As a result, specifications for flat roofs will integrate both the framework and the other elements of the structure.

An average of 80 to 120 euros per square meter is required for the construction of a flat roof , frame, insulation and support included. Since rates depend primarily on your project, it is best to contact a local specialist if you want a more accurate estimate.

If it is the cost of sealing a flat roof that interests you, you will know more by discovering our dedicated page on this subject.

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