Sizes of the Window

If daylight is considered to be essential for the use to which a room will be put, then windows are an unavoidable necessity. Keep in mind how much daylight and nightlight you would want for your room, so consider carefully the sizes of the window. Simple apertures for daylight have developed into significant stylistic features, from Romanesque semi-circular arched windows to Baroque windows surrounded by rich, elaborate decoration.

In the European cultural region lying north of the Alps, the sizes of window and its forms reveal particularly strong features. In contrast to the climatically favoured cultural region of the Mediterranean, daily life here mainly had to be spent indoors. The people were thus dependent upon daylight because artificial light was expensive and good illumination of the room during the hours of darkness was beyond the means of most of the local population.

window sizeWindow sizes for industrial buildings. Every work area needs a window leading to the outside world. The window area which transmits light must be at least 1/20 of the surface area of the floor in the work space. The total width of all windows must amount to at least 1/10 of the total width of all the walls, i.e 1/10 (M + N + O + P) ⟶①.

Window sizes for workrooms. For workrooms which are 3.5 m or more high, the light transmission surface of the window mus be at least 30% of the outside wall surface, i.e. ≥ 0.3 A x B ⟶②.

the rule of window sizeFor workrooms with dimensions similar to those of a living room, the following rules should be applied:

  1. Minimum height of the glass surface, 1.3 m ⟶③.
  2. Height of the window breast from the ground, ≥9 m.
  3. The total height of all windows must be 50% of the width of the workroom, i.e. Q = 0.5R ⟶④.

When calculating the window size for a living room, both the floor area of the room and the angle of incidence of the light must be taken into account ⟶⑤.

Here, ‘a’ is the minimum window size for a living room as percentage of the floor area of the room, ‘b’ is the minimum size for kitchen window and ‘c’ is the minimum size for all other rooms. The angle of incidence of the light is ‘d’.table of window sizes

The larger the angle of incidence, the larger windows need to be. This is because the closer the neighbouring houses are, and the higher they are, the greater the angle of incidence and the smaller the amount of light penetrating into the house. Larger windows will compensate for this smaller quantity of light.

Dutch regulations stipulate the sizes of windows in relation to the angle of incidence of the light.


Example ⟶⑤

‘A’ For a flat, angle of incidence of light 18° – 30°.

‘B’ Necessary window size for the living room.

‘C’ 17% of the room floor surface area is sufficient fo the size of the windows.

The slope of the surface is known. A skylight with a slope of 0° needs to be 20% of the size of a vertical window to make the room equally bright – however, there is no view. Windows are generally the poorest point in terms of heat insulation. For this reason, it is convenient to fit the room with smaller windows, as long as the solar heat gain through the windows is discounted.

As well as the window size and the slope of the window surface, the siting of the house plays and important role. A free-standing house admits more light with the same surface area of windows than a house in the city centre.

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