Passive Solar Green Home Design
Clerestory windows are built above the line of sight atop roof lines, bringing daylight, warmth (in winter) and ventilation into the inner spaces of a building. Originally designed for ancient temples and cathedrals in the 1300s BC(!), today they serve an important function in certain passive solar home designs.
Clerestory windows are ideal for providing daylighting and warmth in rooms where natural daylight and solar heat would otherwise not be available. Clerestories help to even out interior temperatures and give north facing or interior spaces rich, natural daylighting that is typically enjoyed only in south facing rooms. Clerestory windows also provide a unique ‘window’ to our natural world.
Imagine lying in bed watching the moon track across the night sky or stars twinkling above. Clouds and birds glide by, trees bend in the wind and airplanes pass. Clerestory windows offer a unique view to the outdoors while also providing privacy, since they rest above the gaze of passers-by.
In designing a passive solar home, we aim to incorporate south light into as many rooms as possible, since south light also provides natural heat in the winter and day lighting year round. Overhangs, when sized correctly for the latitude, block direct sunlight and solar heat from our homes in warm weather but allow the sun’s warmth to naturally heat our homes when heat is needed in the cold seasons. The same holds true for south facing, clerestory windows.
Ventilation is important for air quality in a healthy home and can be achieved naturally or mechanically. Operable clerestory windows, in conjunction with low operable windows, create passive, natural convection. Cooler outside air is more dense and heavier so it sinks closer to the ground and enters through lower windows. The cooler air pushes less dense, lighter, heated air out through high, clerestory windows, providing the home with a constant flow of fresh air. In the summer this natural thermosiphoning keeps a home cooler and ventilates exhaust air without the use of mechanical devices. In winter the same can happen and is often utilized on sunny mild days. In harsher winter climates, mechanical systems are often preferred in the winter.
Clerestory windows are an effective design strategy and they provide a valued function in passive solar homes. There is a reason they’ve stood the test of time.