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Many energy-efficient houses, whatever the country and climate zone, look much the same as standard houses. Only by cutting away a section of the house would the differences be revealed. However, there are some far more radical possibilities.

Straw-Bale Houses

Photo courtesy of Solarhaven.org Straw bales can be used in constructing a very snug, energy-efficient house.

Straw-bale houses look much like traditional houses. Instead of wood or masonry and insulation, the walls are made of straw bales, which are then covered with stucco. The first straw-bale homes in the United States were constructed in Nebraska starting in about 1900. Straw was cheap and readily available. The newly invented baling machine bundled it into shapes ideal for construction. The houses and other buildings were quick to build and proved well insulated and durable. Some of the earliest structures still survive. Interest in the straw-bale construction method faded by the 1950s but was revived in the 1970s. However, it faced initial resistance from local building authorities, who questioned its fire safety. Straw bales are now widely favored as an environmentally friendly building option, but they are not yet universally approved.

Photo courtesy of Straw Bale Innovations, LLC Once the straw bales are in place and the exterior envelope is completed, mesh wire is put over the walls. Stucco and plaster can then be applied. When completed, a straw-bale house looks like any other house.

There are two main forms of construction. The original Nebraska builders used the bales as load-bearing walls supporting the roof. More common today, and the only way that many building authorities in the United States will allow, is a non-loading-bearing approach. In this case the basic structure is supplied by wood frame, while the straw bales are used as in-fill. Either way, both the interior and exterior of the walls are then covered in mesh and thickly plastered and stuccoed.

Straw is very easy to work with, but it must be kept absolutely dry. For that reason the bales are raised above the ground by the foundation, and wide overhangs are used to keep water away from the base of the building. The plastering material keeps the bales dry while allowing the walls to breathe. The tightly packed straw is not particularly flammable; moreover, it is protected by its thick plaster covering.

Straw-bale houses are very energy efficient, because the straw provides excellent insulation. Similar houses have been built in Europe, Australia, and China.

Earth-Sheltered Houses

Some houses use the soil to moderate temperatures indoors during all kinds of weather. These buildings have the advantage of far greater protection from the elements than a typical aboveground house. Wind and extremes of temperature have relatively little impact on the interior. Because most of the exterior is covered with earth, the house has natural soundproofing.

There are different types of earth-sheltered houses. A bermed design has some walls surrounded by earth but at least one face exposed. Bill Gates, the founder of Microsoft, built a house in this style outside of Seattle, Washington. Bermed houses may be built in either of two styles. In an elevational design, the house is built into a hill with only one side exposed. The exposed side usually faces the equator, to take full advantage of solar heat and light. A penetrational design is built on a flat area with earth piled up around and on top of it. This type of house may have windows on several sides and thus has the advantage of cross ventilation. Both types of design have a long history.

Another type of earth-sheltered house is the buried house, built entirely below ground level on a flat site. This house receives light, solar heat, and natural ventilation from a central atrium. At ground level the house is barely visible, so it is private and quiet, even if located in a city. The construction materials for buried houses need to be strong and readily waterproofed to withstand the pressure and moisture of the surrounding soil. These materials include reinforced concrete, which is used most often; solid masonry is a slightly less expensive alternative but needs reinforcement. Steel is good for framing, but it must be encased in concrete to prevent corrosion.

Earth-sheltered houses face two crucial issues: moisture and ventilation. They must have adequate protection from moisture. The site needs to be carefully chosen, and drainage must be properly designed. The exterior walls must be sheathed in several layers of waterproofing material. Materials used include rubberized asphalt, plastic and vulcanized sheets, liquid polyurethanes, and bentonite. Ventilation is crucial. Moisture and various gases and other pollutants can easily accumulate, and careful planning for this is essential.

Green Roofs

Some earth-sheltered homes have roofs of grass. But a green roof can be put on any building that has a flat top and has a strong enough structure to bear the weight. This type of roof provides terrific insulation, keeping the building warm in winter and cool in summer. It has the additional advantages in urban areas of reducing runoff into the sewers, absorbing pollution and storing carbon, reducing noise, and even serving as a place to grow vegetables. Green roofs are traditional in Norway and have been in use for a long time.

The main drawback is that green roofs are heavy. For an intensive green roof, one in which you can grow relatively large plants, you need a minimum of 0.3 m (1 ft) of soil. The soil must be placed over a waterproofing membrane and probably several other protective layers. Even dry, that much soil is very heavy; when wet, the weight increases significantly. If the roof is to be covered just with grass or a ground cover, less depth of soil is required, but weight is still an issue. Green-roof designers have come up with various lightweight soil mixtures to address this problem. One of them has the virtue of using recycled material. It mixes compost (locally generated) with recycled polystyrene for a truly “green” roof.