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Modern houses use a lot of energy. We heat them, cool them, and light them inside and out. We use electrical appliances that allow us to cook faster, watch television and movies, listen to music, or explore the world by computer. A 2007 report showed that houses are the single largest user of energy worldwide, accounting for 25% of global demand. The United States leads the way, with its large houses, fondness for electrical appliances, and development of subtropical and desert regions of the country.

There are two main power sources for buildings. Electricity provides the power for lights, air-conditioning, and appliances, as well as heating many homes. Fossil fuels, either oil or natural gas, are often used in homes to make heat and hot water. In addition, in many locations around the world, the power used to generate electricity comes from fossil fuels such as coal. Either directly or indirectly, then, the world’s housing is consuming increasing amounts of energy derived from fossil fuels.

As we know, those fuels pump carbon dioxide (CO2) and other greenhouse gases into the atmosphere. Thus buildings, especially houses, make a huge contribution to pollution and global warming. In the United States, residential and commercial buildings are responsible for 48% of greenhouse gas emissions. Around the world, buildings account for somewhat less, about 30%. So, how can we make homes and buildings more energy efficient?

There are many ways to reduce the amount of energy we use in our homes and buildings. We can turn off appliances and lights that are not in use. We can adjust the thermostat to use less heat in cold weather and less air-conditioning in hot weather. Energy-efficient products, including furnaces, water heaters, refrigerators and other appliances, and even lightbulbs, can replace older, less efficient models.

These steps help, but the bigger problem lies in the construction of buildings. If a building is not properly insulated in the exterior walls, the roof, and around pipes, it loses heat in cold weather and cool air in warm weather. Inefficient windows present similar problems. In fact, some estimates say that the world loses as much as two-thirds of the energy used for heating and cooling through poor insulation and leaky pipes.

So, how do we build energy-efficient buildings? Can existing houses and buildings be remodeled or retrofitted to save energy? For both, some of the options are simple and inexpensive. Others are complex and cost a lot to do. All, however, will reduce the amount of energy used. This cuts down on the amount of CO2 emissions, thus lessening the “carbon footprint” of each building or home. Increased energy efficiency also saves money, by lowering energy costs. Many countries offer financial incentives for such improvements.

Heating and Cooling the Natural Way

Before the development of modern heating and air-conditioning systems, people all over the world learned how to build and position their houses to take maximum advantage of heating by the Sun and the cooling effect of shade and breezes. This approach, known as passive heating and cooling, is having a resurgence. Many of these techniques have been around for ages. Today builders are starting to make use of these passive techniques to make homes more energy efficient.

Passive heating makes use of the Sun through positioning of the house and use of building techniques and materials that absorb heat. Cultures as diverse as the ancient Greeks and Romans and the Pueblo Indians of the United States knew how to use the Sun to warm their buildings this way.

Cooling techniques use shade, breezes, and water to reduce the indoor temperature. Courtyards with fountains were common in the buildings of many warm countries, and ancient Persians and other peoples from the Middle East and northern Africa developed structures to cool their houses. In humid tropical regions, buildings had ventilation that allowed the warm air to move out with the breeze.

Current passive techniques use the same ancient, local materials, such as stone, adobe, hay bales, and native wood. Local materials consume less energy in their manufacture and transportation. There is even a place for products of the modern world—for example, used tires, which absorb heat, or modern glass, which can retain heat from the Sun.

Single-Family versus Multifamily Dwellings

One way to increase energy efficiency is to minimize the surface area of the outside walls of a building relative to the amount of occupied space. It is these external walls, and the roof, through which heat is lost in winter and cool air escapes in summer.

Multifamily houses come in many shapes and sizes. Large apartment buildings have many floors and multiple apartments on each floor. Smaller buildings may have six floors or fewer, with a few apartments per floor. Some buildings have a long rectangular shape, with many apartments on only two or three floors. Attached houses have exterior walls in front and back and common walls on either side. The one thing all these different types have in common is an increased number of interior walls and only one roof. That gives these types of buildings a lower potential for energy loss.

In some multifamily buildings, other factors may lessen the energy savings. Poorly constructed buildings may leak energy through windows, doors, and other gaps. There is often less control of heating for each dwelling, particularly in the largest buildings. Common areas such as hallways and lobbies require electricity, if not heat. In addition, large buildings need elevators to move people up and down the different floors.

New Construction

The simplest way to make an energy-efficient building is to start fresh. New buildings can easily integrate passive heating and cooling techniques, materials that will help the building lose less energy, and energy-efficient products most appropriate for the climate. In addition, new construction can incorporate alternative energy-production options, such as solar panels or geothermal heat pumps, to decrease reliance on fossil fuels.

	Digging Deeper Find out more about The Solar Decathlon.

Many countries, states, and cities have created “green” building standards for new construction. Standards vary depending on the hemisphere, climate, and materials available locally, because different climates require different design strategies and different materials. Most important, builders need to consider the interrelationships of all these elements. This is called the “whole-house approach.”

Energy-efficient buildings may not look much different from the more traditionally built houses around them. However, some builders take a more radical approach. There are earth-sheltered houses, as well as ones that use materials such as old automobile tires or straw bales for walls.

Renovation

Realistically, most people can’t start new: We need to work with existing houses or buildings. There is still plenty that can be done, though. The starting point is an energy audit. This tells you how much energy a building uses, how much energy it loses, and what measures can be taken to make it more energy efficient. The energy audit checks for air leaks from and into the building and assesses the adequacy of its insulation. Heating and cooling equipment and electrical appliances can be replaced as well, to increase energy efficiency. Some techniques from new construction can also be applied.

For energy-efficient construction, we can learn from the past, we can learn from nature, and we can use the innovations of high technology. Let’s take a closer look at passive heating and cooling methods and how they can make a building more energy efficient.