What are Passive Solar Houses?

Passive solar houses are homes that are designed to take advantage of the sun’s heat in the winter, effectively heating the home without using electricity or mechanical devices. A passive solar home also reflects the sun’s heat during the summer. The homes are built using a combination of heat-absorbing materials and room designs that promote the natural movement of heated air. Windows that face the winter sun and overhangs that protect windows from the summer sun are additional strategic tools. Homes designed this way have lower heating and cooling costs.

There are five main elements to passive solar houses: collectors, absorbers, thermal masses, natural distribution, and control. These five elements work together to collect and store heat from the sun. A simplified explanation helps to understand the principles behind passive solar construction.

Sunlight enters through a collector, such as a window. The sunlight hits an interior wall, the absorber. The absorber transfers the heat, using conduction, to the material inside the wall. The material in the wall, the thermal mass, holds the heat.

As the house cools in the evening, the warm thermal mass releases heat to the cooler air. The greater the thermal mass, the more heat that is released. The warm air rises as the cooler air sinks. A combination of vents, louvers, and design elements help move the heated air and distribute it throughout the house. Awnings, overhangs and low-emissive coatings on the windows keep the house cool during the summer.

Passive solar houses are built with most windows facing the winter sun. Closets and storage spaces are located on the opposite side to help provide a buffer from the cold. The houses are made with building materials that have a high thermal mass. High thermal mass materials include brick, stone, and concrete. Water is an exceptionally high thermal mass material, and some passive solar houses incorporate containers of water within the walls.

Several building elements are incorporated into passive solar houses to increase the heat gain. Sunrooms, or sun spaces, are built on the side of the house that receives the most sun. These rooms are built of glass or plastic and collect a large amount of heat during the day, which is easily released into the house at night by simply opening a connecting door. Trombe walls are thick interior walls made of a high thermal mass material. These walls are strategically built into the solar house in locations where they will receive large amounts of sunlight.

There are many advantages to passive solar houses. They have lower electric costs due to lowered heating and air-conditioning demands, and they have higher resale values. The houses are quieter than traditionally built homes due to increased insulation, denser building materials, and the absence of the hum of heaters and air-conditioners.