For Stan Luhr, it's an easy choice. Venting a home's plumbing system through air admittance valves, rather than piping, "reduces builders' risk and cost at the same time," says Luhr, president of Quality Built, a Poway, Calif., firm that inspects new homes for builders.

Traditionally, a home's plumbing system is vented to the outside through pipes that run through the house, into the attic, and through the roof. These vent pipes "allow a little bit of air into the sewer system when someone is flushing a toilet or draining a bathtub," Luhr explains. Air admittance valves do the same thing but without the extra piping, fittings, or labor. They are installed directly into the plumbing system--typically inside the sink cabinet--and open and close as needed.

And they do it for a lot less money. Luhr estimates that using the valves, which are manufactured by Studor Inc., and list for $20 to $40 each, depending on size, saves $300 in plumbing and labor costs per house. The valves also reduce the chance of construction defects (like a leaky roof) from improperly installed venting.

There are some challenges. Plumbers, who install the valves, don't necessarily like having their job downsized. And, despite the fact the valves have been used in Europe for 30 years and approved for U.S. use since the 1990s, local building departments can be wary, so builders should talk with them first. But Luhr says the payoffs for using the valve warrant persistence. "We've seen many litigation claims from dry vent problems, from damage done during or after installation," he says. "Even if a valve fails, you just unscrew it and put in a new one."