Mayors from around the world are meeting in San Francisco for the United Nations Green Cities conference through June 5, where they are hearing about ways to improve the environment. They are also sharing tips on eco-friendly practices, including those that apply to business. The meeting is giving San Francisco firms a chance to highlight what they are doing to help the planet.

Home builders could make better use of construction materials, says John Peterson, founder of the organization Public Architecture. He designed a two-story house made with discarded material, which is on display near city hall, where conference delegates are meeting. "A part of your house might be out of salvage materials. For instance, one of the things we want people to understand is that there are a lot of really fine materials that are being thrown away all the time. The glass in these walls is very, very high quality glass, very expensive. This is being thrown away. If you're flexible about how you think you design your house or your building, you can incorporate these kinds of things very inexpensively," he said.

Old doors are reused, floor tiles are made from leather scraps, and telephone books are used for insulation. In San Francisco, construction debris is also being recycled.

San Francisco recycles material from construction and demolition sites, known as C & D sites. A stream of trucks arrives each day at this recycling plant outside the city. "This is where all the C & D material comes from San Francisco, all the debris boxes, construction, demolition material. It's being tipped on to that floor there. This loader is loading up the material. It goes into this in-feed conveyor, up over the top through a series of shaker screens. And there are 10 sorters. They pick all of the sheet rock, wood, metal, plastic, cardboard," said

Ken Stewart, the operations manager.

Most of it is reused.

Dozens of local companies are showcasing their efforts to help the environment at a trade show being held in connection with the United Nations meeting. Tomek Rondio of the company Mortgage Green provides financing for home buyers who also want to help the environment. The company donates 10 percent of its gross profits to environmental groups that include the Rainforest Action Network and the National Campaign for Sustainable Agriculture. "We're actually serving as a business model to prove to the world that you can be socially and environmentally conscious and support wonderful organizations that really are trying to save our planet, and do good business in a tradition sense at the same time," he said.

Across town at the Slanted Door Restaurant, executive chef Charles Phan recycles uneaten food, which is turned into compost and used as fertilizer. He also uses biodegradable containers made of corn starch for customers who buy food at his take-out counter. "The philosophy is really to provide sustainable meat and food to support sustainable small farms. And recycling is really just part of the program. It doesn't make sense when you try to eat healthy and you're ruining the environment," he said.

In nearby Berkeley, a company called Clif Bar makes high-energy snacks from fruit, nuts and organic soybeans. The company has a staff ecologist, Elysa Hammond, who says Clif Bar has eliminated waste from its packaging, improving the environment and saving money. "It makes good business sense for the long-term sustainable view. But in the short term, if you're reducing waste, you're usually saving money. So when we redesigned our cardboard caddies that hold our Clif Bars, we got rid of 90,000 pounds of shrink wrap a year," he said.

Redesigning the display boxes saves $450,000 a year. Using recycled paper saves another $50,000.

Clif Bar founder Gary Erickson says the company needs to make money, but that it also has a mission. "Taking care of our people and our brands and our community and the planet. Not many companies have really balanced all those things together and tried to be responsible and steward all those. And a lot of companies that started off trying to do it, they're now owned by multinational corporations," he said.

He says maintaining that vision is difficult in a publicly owned corporation, whose officers must answer to shareholders. But he says in any kind of company, preserving the environment is good business.