How to Calculate the Roof Pitch?

Roofs often play important roles in a project's identity. In addition to the aesthetic aspect, they play a fundamental role in protecting and closing the building. Of the existing types of coverage, pitched roofs are the most common in homes and buildings all around the world, therefore, it is necessary to ensure that they are within the parameters set out in the technical standards.

We call roofs those structures that close the top of buildings, protecting the inside from all weather, such as rain, wind and sunlight. They can acquire different formats and even gain new functionalities depending on the project's identity: they can be flat, pitched, with a variety of planes or they can be visited and vegetated. Within this variety, pitched roofs are the most used in residential architecture, and even in building roofs, given their practicality and low execution cost.

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Pavilhão para Estacionamento de Bicicletas / WAW architects. Image © Tim Van de Velde

The conventional pitched roof is basically composed of two elements, the frame and the tiles. Usually, the structure consists of wooden or metallic pieces, while the tiles have a variety of types, which can be fiber cement, ceramic, aluminum, concrete, among others. Each of these materials has its cost, maintenance and labor specifications, as well as its performance for building thermal comfort. The roof pitch is determined by the types of tile.

The tiles can be a sum of several small pieces, such as ceramic tiles, concrete and some PVC, or they can also be a combination of large plates such as metal or fiber cement. Each of them have their own properties such as weight and fixing methods, however, the general rule is that the smaller the tile, the greater the possible inclination. At the same time, regardless of the type of tile, the way of calculating the pitch of the roof is the same: a percentage that relates length to height.

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Instituto de Ensino Secundário Serra de Noet / Fabregat & Fabregat Arquitectes. Image © Joan Guillamat

Geometrically, for every 1 horizontal unit, there is a value related vertically, resulting in a right triangle where the hypotenuse is the plane of the roof and the ratio of a divided by b is the percentage of the slope:

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Como calcular a inclinação do telhado?. Image © Giovana Martino

  • Thus, to reach the roof pitch, a straight line of 1 meter on horizontal is determined;
  • From this straight line, the direction is changed to vertical, going up as much as desired, 10 centimeters, in the case of a roof with a pitch of 1%, for example;
  • Finally, the triangle is closed with a straight line that forms the roof pitch.

There are manufacturers' standards and norms on the market that regulate the use of each of these materials, and it is important to follow what is indicated in the manuals to ensure both the correct flow of water and the proper fixation against the action of the winds. For ceramic and concrete tiles, for example, the average pitch is 30%, while fiber cement roofs and metal tiles are between 9 and 10% pitch. Incorrectly used tiles can cause leaks, short circuits, unroofing, and other accidents.

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Casa e Restaurante The Quê / 23o5Studio. Image © Hiroyuki Oki

In this way, understanding the roof as an identity element of the projects, in which architecture is often more freely expressed, it is essential, during the project, to add technical issues to the design that guarantee feasibility and full functioning.

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Cite: Martino, Giovana. "How to Calculate the Roof Pitch?" [Como calcular a inclinação de um telhado? ] 31 Jan 2022. ArchDaily. (Trans. Simões, Diogo) Accessed . <> ISSN 0719-8884

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