Uniformity of daylight across an entire room is the objective of good window planning. Having dark corners and high brightness contrasts is undesirable in any room. Some of the factors that will affect daylight within a room are: the direction which the room faces; the shape and position of the windows in the wall; the type of glass used; the amount of light reflected by ceilings, walls, floor and furnishings; and the type of sunlight controls used inside and outside the house.

To ensure even distribution of the greatest amount of daylight within a room, consider the following tips when designing your home:

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If one large opening is provided instead of several small ones, a more desirable distribution of light is secured. Dark areas between openings are eliminated.
pg aluminium window planning pg aluminium window planning
A horizontal window gives a wider spread of light than a vertical window of the same area.
  • Provide glass areas in excess of 20% of the floor area of each room. This is a general rule of thumb. Most building codes recommend that the glass area be not less than 10%, but much more is desirable to meet daylight requirements on cloudy days. On brighter days, the amount of light can be controlled by interior and exterior shading devices.

  • Place the main window area toward the north, except in hot climates where a southern orientation is favoured in order to limit heat from the sun. The north sky is considerably brighter than the south sky. A northern exposure permits the maximum amount of daylight and also the greatest amount of solar heat in winter.

  • Group window openings in the wall to eliminate undesirable contrast in brightness. Provide one large opening on a wall instead of several small ones to do away with dark areas between openings.

  • Select the window shape that gives the desired distribution of light within each room. For a broad, shallow distribution of light, use short, wide windows. Tall, narrow windows give a thin, deep distribution of light. Intensity of light is great near the window and then drops off rapidly and smoothly within a short distance.

  • Place the window as high in the wall as possible to lengthen the depth of light penetration into the room. If possible, place the top of the window close to the ceiling. More sky is visible through the upper parts of the window than the lower, moreover, the overhead sky is brighterthan the sky at the horizon.
  • pg aluminium window planning pg aluminium window planning
    The higher the window is placed in the wall, the deeper
    is the penetration of light.
    pg aluminium window planning
    Windows in more than one wall give more effective daylighting than windows in just one wall.
  • Use windows in more than one wall for greater admission and better distribution of daylight.

  • Do not specify corner windows or bay windows as a means to increase the daylight effectiveness of the window. The actual area of glass is greater and more costly than the effective daylight area obtained.

  • Screen only those parts of the window that open for entilation. Full screens on a double hung window can absorb as much as 50% of the available daylight. Half screens absorb only 15%.

  • Finish ceilings and walls (and even the floor if practical) in light colours to take advantage of light distribution made possible by reflection. Use flat or dull finishes. Furnishings, especially curtains, should also be light in colour.

  • Mount curtains, shades and other window hangings above the top of the window and to the side of the window frame, in order to free the entire glass area and thus admit the greatest amount of light. Dark, heavy curtains hung over the sides and top of a window can reduce the available daylight. The practice of pulling window shades one-fourth ;or one-half of the way down results in loss of light at the rear of the room where it is most needed.

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