Think of the atmosphere as an insulating glass window and the earth and and the ocean as thermal mass (large bodies that store heat and moderate temperature). Every square meter of sunlight contains around 1,000 watts of energy— about the same wattage as an electric hair dryer. Additionally, nature is extremely efficient. Even a relatively small cumulous cloud that you see floating across the sky can easily weigh millions of pounds , and it can carry massive amounts of water, enough to fill dozens of tanker ships. Yet it quietly floats above our heads, moving water to the tops of mountains and around the globe. How elegant is that? No pumps, oil, or electricity are needed.

We humans tend to be mighty pleased with ourselves due to our mechanical inventions that heat and cool the air in our buildings, pump water, and generate electricity with coal and oil. Our real design challenge will now be to start to emulate nature and take advantage of the millions of years of design expertise that nature has developed.

The roof overhang is designed to prevent direct sunlight from entering the home in the summer.

For example, one of the basic principles of designing an energy-efficient home is to face the longer side of the building towards the south (when your home is in the Northern hemisphere). This simple idea, combined with a properly designed roof overhang, will greatly reduce the cost of mechanically heating and cooling the home. Best yet, a southern orientation will add nothing to the construction cost. With a large amount of window space on this side and a properly designed roof overhang, solar energy will be able to enter and heat the home in the winter. Depending on your location, this solar heat can supply the majority, or at least a good portion of your heating needs, assuming that the rest of the home is also appropriately designed. During the hot summer months when the sun is higher in the sky, a properly designed roof overhang will help keep the home cool by shielding the inside of the home from all direct sunlight, thus eliminating or reducing the need for air conditioning (when combined with interior thermal mass and appropriate insulation).

In the next column I will discuss other green design elements that add nothing to the construction cost.

See also: Part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, part 10, part 11, part 12 and part 13.

[This has been a guest post by Ted Owens, a green designer and filmmaker. More details on green building design and construction can be found on his website and in the Building with Awareness DVD and Guidebook. -Ed.]