 # Calculate the Area of ​​a Roof

Calculating the area of ​​a roof depends on the shape and structure of your roof. This calculation is essential during renovation or insulation work, for example, the calculation formulas are quite simple to use.

## Why calculate the surface of a roof?

The calculation of the surface of a roof makes it possible, logically, to know with precision the surface of your roof. This may be of particular use to you:

• If you want to carry out a renovation or repairs on your roof  ;
• If you need to lay a roof covering  ;
• If you are carrying out insulation work on your roof  ;
• If you plan to install gutters on your roof;
• If you want to change the structure of the roof.

Thus, whether you do your roofing work yourself or call on professionals, estimating the surface of the roof will be essential to know the type of suitable roofing, the materials, and their dimensions… of course estimate the total budget for the renovation of your roof!

## How to calculate the surface of a roof: depending on the type of roof

If you want to calculate the surface of a roof, know that this operation depends above all on the structure of your roof, namely whether it is a flat roof or a pitched roof. In this respect, we therefore distinguish:

• The calculation of the surface of a flat roof  ;
• The calculation of the surface of a roof with 1 or 2 sides  ;
• And the calculation of the area of ​​​​a roof with 3 or more sides.

## Calculation of the area of ​​​​a flat roof

Due to the total absence of slope, the estimation of the surface of a flat roof (also called “terrace roof” or “terrace roof”) is the easiest to perform! As a flat roof will necessarily be square or rectangular in shape, the calculation of the surface of a flat roof is simply done by multiplying the length by the width.

Flat roof area = length x width.

For example, for a square roof terrace with a side of 10 m (length and width), we obtain 10 mx 10 m = a roof surface of 100 m².

## The calculation of the surface of a roof with 1 or 2 sides

The calculation of the surface of a roof with 1 or 2 sides is a little more complicated because it is now necessary to take into account the slope (or slopes) of the roof. To calculate the latter, you have to use the good old Pythagorean theorem, and the plans of your house which will indicate the height of the roof at the base of the ridge. So :

• The length of the slope² = Height of the roof (from the base to the ridge)² + horizontal width².
• Let = √ (roof height² + roof width²)

Once you have calculated the length of the slope of your roof, remember that:

• Pitched roof area (in m²) = roof width (in m) x pitch length (in m).

For example, for a roof 10 meters wide and 9 meters long, we obtain 10 mx 9 m = a roof surface of 90 m².

Note: if your roof is two-sided, you will obviously have to multiply the result by 2.

## The calculation of the surface of a multi-sided roof

If your roof has 3 or more sides, the estimate of the surface of your roof will depend on the geometric shape of the latter! In effect :

• If your roof is triangular, its surface will be equal to half the product of the length of its base and its height. In other words:
Roof area (in m²) = (length of the base of the roof x height of the roof from the base to the ridge) / 2.
• If your 4-sided roof has the shape of a trapezium, the surface of the roof will be equal to the product of the average of the bases by its height. In other words:
Roof area (in m²) = (length of upper roof base + length of lower roof base) / 2 x roof height from base to ridge.
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