Most builders know by now that as homes have gotten tighter, indoor air quality has declined. Brian McElroy is proving you can have it both ways.

The president of McElroy Custom Homes near Tampa, Fla., swears by the Epic Wall system, a precast concrete system from Weaver Precast of Florida that provides an R-value of 15.3, withstands winds up to 230 mph, and is watertight at 5,000 psi. The walls come furred, insulated, and factory prepped for finishing. They go up superfast, too: The builder reports crews can set up most single-family homes in one day. In the end, “You virtually have a waterproof and bug-tight house,” says Phil Dunn, vice president of marketing. (Weaver’s parent company, Superior Walls, also offers several efficient precast concrete foundation systems.)

Helping to seal the deal are MI low-E, insulated windows; Therma-Tru Energy Star–rated sliding glass doors; and Icynene spray-foam insulation in the attic. In addition, the builder goes back to fill gaps in the walls caused by wiring and other penetrations, says energy rater Demensio Barton of Essential Rating. Energy testing is conducted a week after the homeowner takes occupancy to ensure actual living conditions.

McElroy began offering the super-tight envelope standard three and a half years ago on the 10 to 15 custom homes, which can range from 1,200 to 12,000 square feet, that it builds a year.

Still, McElroy knew there could be potential drawbacks. “We were concerned that with a house that tight, we might have mold problems if we didn’t do anything to address indoor air quality,” he says. Knowing the tight envelope also meant easy control of the interior environment, the company added mechanical systems to make the homes as healthy as they are efficient.

The houses include a Trane air conditioner of at least 14 SEER; an energy recovery ventilator that exchanges stale indoor air with fresh exterior air; a whole-house dehumidifier; and a UV or HEPA filtration system. Keeping the humidity under control also reduces energy costs because it allows the air conditioner to be kept at a higher setting.

All of McElroy’s homes are Energy Star rated and follow NAHB’s Model Green Home Building Guidelines. McElroy says the homes likely would meet LEED-certification standards as well, but the cost for verification is one he says he would rather let the homeowner spend on additional green features.

Even without the certifications that the techniques help bring, McElroy and his team consider the company’s wall systems and mechanical choices “sacred cows.” “We won’t build a house any other way,” Dunn says.