Window Design III

Architecture Design

I propose to delve a bit more in, probably, the most important architectural element in daylighting: the window. So far we have made two previous notes, as follows:

Window Design II

Window Design I

We will develop the study of the height of the window and how it influences in daylight. Below we can see the model of an office where a longitudinal window is located. The window size is changing from 10% of the façade surface to 75%:

As can be seen, the windows that are between 10 and 20% of the façade surface (equivalent to 4 and 8% of the floor area) hardly provide enough natural lighting.

A window which occupies between 30% and 40% of the façade surface (equivalent to 12 and 16% of the floor surface) achieves an acceptable illuminance, since approximately half of the office is over 300 lux. Windows of larger sizes allows higher luminance. This is shown in false color map that measures the reflected luminance:

Note that the higher the window lintel, the deeper the light, as we deducted in Window Design I.

This work has been developed by the New Buildings Institute, which has done a great job in collaboration with the University of Idaho and Washington. My sincere congratulations for this study.

We will continue studying the windows in the next notes.

Window Design II

Architecture Design

Before looking at the role of other architectural elements, we will delve into the behavior of daylight through windows.

5. - The amount of light is proportional to the window surface: This is a logical argument, because when the window has more surface greater amount of light enters the room [1].  In fact, the window surface is directly proportional to the level of illumination.

6. - The depth of light depends on the position of the window: This statement was already observed in the previous text: an upper window allows a deeper illumination, while avoiding the glare of the occupants [2]. Consequently, if we want the daylight reaches the back of the room, we need upper windows with large surface.

7. - The horizontal windows are better than vertical: Le Corbusier put it well ... The long windows allow more uniform lighting in the room, while the vertical windows create shadowy areas and produce a high contrast.

All these statements can be seen in numerous studies on lighting. Currently, it should be noted the research of Diepens et al. [3], which analyzes the light distribution of different windows in a room.

Later we will talk about the appropriate spacing between windows, to produce uniform illumination.

Greetings and see you soon.

[1] Navarro, J.: Sobre Iluminación Natural en Arquitectura. Universidad de Sevilla, 1983.

[2] CIBSE: Daylighting and Window Design. London: Chartered Institution of Building Services Engineers, 1999. Cap. 2.2.3.

[3] Diepens, J., Bakker, F., Zonneveldt, L.: Daylight design variations book. TNO-TUE Centre for Building Research (en desarrollo, última actualización Octubre 2000).