When a tornado flattened Greensburg, Kan., in May 2008, the city vowed to rebuild -- with a twist. All new municipal structures would be built "green," with businesses and homeowners encouraged to follow suit. Likewise, in New Orleans, where Brad Pitt's Make It Right foundation is constructing new, affordable green homes for Ninth Ward residents displaced by Hurricane Katrina.

Such projects have decisively moved green building from the exclusive realm of the wealthy into the affordable mainstream. But you don't have to see your home flattened by a natural disaster or be part of a community-wide initiative to build green.

Many Americans -- spurred by the need to save money and energy or to create a healthier indoor environment -- are incorporating green building concepts into existing homes and businesses, either through small upgrades or major renovations.

The truth is that most of our country's buildings just aren't very efficient. Forty percent of all U.S. energy goes to heat, light, and cool buildings, hitting all of us in our wallets and generating 43 percent of our nation's carbon dioxide emissions.

So how does each one of us join the green rebuilding revolution? An energy audit -- often offered free by a local utility -- is the place to start. It shows where air and energy dollars are leaking from your building and makes recommendations to staunch that flow. Surprisingly, you can improve energy efficiency by at least 30 percent with minor upgrades whose costs are recovered within a single year, according to Brendan Owens, a vice president at the U.S. Green Building Council.

Such upgrades can include resealing seams around doors and air ducts, tuning up mechanical systems, and switching to compact fluorescent light bulbs. You can see additional savings from installing double- or triple-paned windows, good insulation (using recycled materials), or energy-efficient appliances (see the federal EnergyStar website). All these paybacks start immediately: when I replaced my old, inefficient windows with double-paned glass, I saw a 40 percent reduction on my next energy bill.

Conserving water is also vital to our communities and saves money. Flow restrictors on showerheads and faucets, while not very glamorous changes, are cheap and reduce water consumption dramatically. Newer dishwashers, low-flush or dual-flush toilets (offering half-flush and whole flush options), and front-loading washing machines save multiple gallons. On demand water heaters can also save water and energy. Family health concerns are another reason to go green. Indoor environments frequently exude toxic chemicals found in many modern building materials. Even small projects like painting or replacing carpet or furniture are opportunities to make less toxic choices and to protect children who like to taste-test their surroundings.

When painting, use low- or no-VOC (volatile organic compound) paints. These are widely available and look just as good as old-style paint. Carpet now comes in nontoxic, recycled squares so you can take them up one at a time for washing or replacement.

As you tackle green projects, consider construction waste disposal. Doors, windows, cabinets, shutters, appliances and more can be reused, recycled, or given to neighbors, salvage yards, antique dealers, or groups like Habitat for Humanity. Some materials can even be sold for a small profit on websites like Craigslist. Finding new homes for old materials will also reduce your dump or trash fees. Also consider quality, reused materials for your green project; they're typically less expensive than new and are sometimes of better quality.

There are many more green retrofit possibilities. The U.S. Green Building Council's LEED checklist (Leadership in Energy and Environmental Design) can help guide you. You don't need to pay for LEED certification; simply look at USGBC's web site and take tips that make sense for your project. Or read Living Like Ed: A Guide to the Eco-Friendly Life, a book by actor and activist Ed Begley Jr. that conveniently catalogs green retrofits, starting with the easiest and least expensive, and progressing from there.

How much will your personal effort benefit our nation and world? Green architect Ed Mazria, founder of the nonprofit group Architecture 2030, estimates that for every $21 billion invested in the energy efficiency of our buildings, we could close 22 coal-burning power plants, reduce natural gas use by 204 billion cubic feet per year, cut oil use by 10.7 billion barrels a year, and cut carbon dioxide emissions by 86.7 billion metric tons. We'd also save consumers $8.46 billion a year, and create about 216,000 jobs.

If that sounds like a lot of light-bulb changing and window replacing, don't be daunted. Just remember: You don't have to do it all at once. Start small. Learn by doing. Every little bit helps.