How to choose the right roof windows?

  • on 8th January 2021

Correct selection of roof windows to the type of rooms and their number and construction significantly impact the comfort of the attic.

Roof windows are commonly used today. They are technically well-developed solutions ensuring proper lighting of the usable attic and at the same time the possibility of contact between the inhabitants and their surroundings. They also provide the option of adequate room ventilation and support the work of gravity ventilation.

The most important criteria
From the above functions, it is possible to make a general recommendation to choose large-sized windows for attics. These are the windows that best illuminate the room and windows of such a construction that will enable comfortable observation of the surroundings. We can choose from roof windows of pivot, tilt and turn construction, balcony windows and roof windows with a higher pivot axis. Each solution has its advantages and the specific needs of users to determine the choice. Roof windows are selected depending on the purpose and size of the room and on the roof pitch. They can also be made of various materials.


The materials of which the windows are made are selected according to the purpose of the room and users’ requirements. Wooden windows can be used in the attic in most spaces such as bedrooms, corridors and children’s rooms. In rooms with periodically increased humidity, such as bathrooms, laundries or kitchens, plastic-aluminium windows are recommended. On the other hand, for buildings where particular emphasis is placed on energy efficiency, windows with increased thermal insulation may be recommended (in the Fakro offer these are Thermo windows).

Purpose and size of the room
The selection of roof windows is also a calculation of the required number of windows and their size depending on the purpose and size of the room.

Building regulations indicate that the amount of light needed is expressed by the ratio of the window area in the frame light to the floor area in the room. In rooms intended for human occupancy, this ratio should be at least 1:8, while in other rooms where daylight is required due to the intended use, it is at least 1:12. Although Polish regulations do not specify the lighting of roof windows, the principle of compliance with the existing rules applies.

Here is an example of calculating the number of roof windows required to illuminate a room of 20 m2 with daylight. The calculation is based on the required 1:8 ratio and looks as follows: (20 x 1) : 8 = 2,5

This means that for the illumination of a room of 20 m2, 2.5 m2 of window area counting in the frame light must be used. Such a place is obtained by using:

4 windows with dimensions of 78 x 118 cm or
3 windows measuring 78 x 140 cm or
2 windows with dimensions 114 x 118 cm.

Due to the distribution of light in the room, it would be best, in this case, to use four windows with dimensions of 78 x 118 cm in a 2 x 2 arrangement, located on both sides of the roof slope.

Roof pitch angle
This criterion is essential for obtaining proper room illumination and comfort of using roof windows. The scope of installation is specified in the installation manual. The general rule is that the smaller the roof pitch, the higher the window height should be.

Window installation height
The height of window installation is closely related to other window selection factors and guarantees proper illumination of rooms. The regulations indicate that in buildings with storeys below 25 m above the area, the distance between the bottom edge of the window opening and the floor should be at least 85 cm. However, on storeys over 25 m above the area, no less than 110 cm should be kept. The higher the window is installed, the better the room will be illuminated. According to the regulations, the transparent window surface’s upper edge should be at least 220 cm above the floor. Additionally, comfortable operation of roof windows is ensured by using the lower handle.

The installation height of roof windows with ventilators is also essential. For example, in Fakro windows, ventilators are located in the upper part of the frame. For the installation to meet the regulations, their upper edge should also be at the height of 220 cm. Fakro recommends installing roof windows at the level of 110-140 cm from the floor (bottom edge). A window installed to make it possible to place a standard radiator under the window and make the slats correctly. Proper air circulation in the window recess is ensured, effectively reducing the risk of condensation on the roof window.

Three installation rules
Taking into account all the remarks made so far, it can be concluded that three general rules should be followed when selecting and installing windows.

Firstly – better lighting effects will be achieved by using several windows located on different roof points than windows grouped in one place.

Secondly, the higher the window is installed from the floor, the better and more evenly lighted the room will be.

Thirdly, high roof windows ensure even distribution of light in the room and guarantee a view to the outside. It should also be remembered that only proper installation of a window in the roof will allow for long-term and trouble-free use.

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