Which Roof Opening to Choose

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Roof openings: light and air

Types of roof openings

2 types of openings for rounded roofs

3 types of openings for flat roof

The various elements that make up a roof are successively assembled to form a solid, resistant whole that also ensures the circulation of air: the framework, the insulation elements, the screen under the roof, the ventilation and the space under the roof, the roofing, the water evacuation and the roof openings. These are of several types and differ according to the shape of the roof.

Roof openings: lighting and ventilation

If the room immediately under the roof is used, it can be lit and ventilated thanks to one or more openings placed in the roof, often visible from the outside. These openings are used to:

light the room or the attic located under the roof;

ventilate the room or the attic under the roof (depending on the type of opening).

Good to know: installing a roof opening requires the creation of an opening in the frame (the hopper) and the implementation of a device to reinforce it.

Types of roof openings

Roof Opening

From the most aesthetic to the most practical, the choice of roof openings is vast:

The cat flap: a small opening used to ventilate the roof.

The roof window: opening specially designed for roofs (at least 15°):

  • larger glazing area than the skylight frame;

convenient to install;

opens by rotation or projection-rotation;

has a ventilation position.

The skylight frame: a glazed frame can be fixed or opened.

Skylight: looks like a small house set on top of the roof;

has openings on its walls.

The dormer window: adds charm and volume to the roof. This vertical window consists of the following:

  • one or more openings;
  • two walled or glazed sides;
  • a roof.

There is a large variety of them. The different types of dormers are distinguished by their shapes. For example:

The bull’s eye is a circular-shaped window.

The trestle dormer or jacobine, which is the classic form, is topped by a gable roof.

A three-sided rooftops the capuchin or hipped dormer.

The roof opening can therefore be discreet or showy, bringing a regional, classic, luxurious or modern touch while ventilating and sunlighting the space under the roof.

2 types of openings for rounded roofs

A rounded roof cannot accommodate all types of openings. Indeed, the shape of the roof is not always adapted to the installation of a skylight. Only a professional can tell you if your chosen opening is technically feasible.

On a rounded roof, two types of roof openings are preferred:

  • The skylight;
  • The roof window.

Good to know: today’s professionals create openings that follow the shape of the roof.

3 types of openings for flat roofs

Because of its particular shape, the flat roof can only accommodate certain types of openings. Indispensable for letting in the sun and sometimes for ventilation, there are three types of openings adapted to flat roofs:

The glass block

Glass blocks are small cubes installed in the screed when poured. They simply allow light to enter but not to ventilate the room or to see outside.


Skylight is mainly used in industrial buildings. The skylight consists of a curved window, often opaque, sometimes openable with a cable.

The roof window

These are the same roof windows as sloping and rounded roofs. The only difference is that the slight slope is compensated by a sloping support so that water does not stagnate on the window;

The roof window, therefore, protrudes from the flat roof.

Now you know which roof opening to choose from. Remember to share your experience in the comments below.


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