Passive solar design means using a building’s site, climate, design, and materials, to best manage how sunlight enters the space and minimise overall energy use. It includes four key principles: orientation, solar gain, thermal mass and shading.

Orientation

By orientating the windows of the main living spaces towards the sun, it is easiest to manage how sunlight enters the building. In the northern hemisphere that means facing due south, or due north in the southern hemisphere, though up to 30^o east or west is still workable. Eco-development such as Village Homes in Davis, California, are designed with all streets running east-west to ensure every house can have the best orientation.

Solar Gain

Capturing the sun’s energy can meet a large part of the demand for space heating, and this is what we call solar gain. Simply letting the sunlight in through windows is the simplest way, or we can use dedicated sun spaces (what you might also call a sunroom or glasshouse) to increase the effect. The Oxford Ecohouse by Prof Sue Roaf is a great example of how a sunspace can be inegrated to the design.

A traditional technique to more actively manage solar gain is a Trombe Wall, where a sun-facing wall is covered with glass, creating a void where the heat is carried by airflows into the rooms. Solar thermal hot air collectors work in a similar way.

Solar gain does need to be carefully managed, as too much sunlight during hot weather can lead to overheating of the interior.

Thermal Mass

The idea behind thermal mass is to absorb heat when it’s too hot, and then release it again when it’s cooler. This is beneficial in both cold and hot climates as it helps to balance out daily temperature variations. Any heavy dense material that readily absorbs heat is useful for thermal mass, such as masonry floors or walls. You can also use feature walls designed especially for this purpose, or even water containers as water has high thermal mass.

Shading

We’ve made the point a few times that Passive Solar Design is about “managing” solar gain, and shading devices are the main way to do this. It could be as simple as an eaves overhang which is dimensioned to let the low winter sunlight in through windows but cut out the higher summer sun. You can also use external shading devices such as awnings and trellises, or internal blinds and curtains. Deciduous plants can also help control seasonal variations.