When home builders gather in Orlando for various trade shows, the “modular homes” erected in the Orange County Convention Center’s parking lots are always a big hit.

The houses go up in a matter of days, using factory-built parts, or modules, shipped to the site for quick assembly. Construction waste is minimal compared with site-built houses. When the trade show is over, the homes are taken apart and trucked away.

Now those modular homes – which increasingly rival or surpass the quality of conventionally built wood or block homes – are eligible for environmentally sound, or “green,” certification from the National Association of Home Builders.

Modular builders say that milestone, recently announced by the Washington, D.C.-based trade association, is a big step toward broader recognition that the modular approach to housing is competitive in more ways than simply price and speed of construction.

More and more builders are entering the “systems built” field. The NAHB estimates that modular homes now account for about one-fifth of all homes built every year, a market share that’s expected to continue rising as the technique is refined and expands. By constructing walls, roofs, floors and other parts inside big factories where the weather does not interfere or slow the process, a builder reduces labor costs and boosts productivity.

The new certification process, called Modular Green, is being offered by the NAHB Research Center, which also administers the National Green Building Certification program for conventionally built homes.

The original verification service for conventional homes was launched in Orlando in February as part of NAHBGreen, a comprehensive energy-efficiency and resource-conservation program announced during the builders’ big annual conference and trade show. (The NAHB’s giant annual gathering, known as the International Builders’ Shows, moves to Las Vegas for the next two years but returns to Orlando in 2011 and 2012.)

Because factory-built, modular homes take advantage of efficiencies that make the homes and apartments less expensive to produce, the process results in less waste – an inherently “green” advantage,” according to industry professionals.

To gain green certification from the builders’ association, conventional homes are inspected on-site by NAHB Research Center-trained “verifiers” who examine the insulation, framing and other components of the building’s exterior. They also check for materials and products that help achieve water efficiency, indoor environmental quality, and other aspects of green construction.

Modular, or systems-built, homes must meet the same government building codes as site-built housing. But inspectors can’t see behind the walls when pre-built components arrive at the work site, making the green-verification process more difficult. So the verifiers check components during construction in the factory, then inspect the rest of the work on site.

The NAHB Research Center, based in Upper Marlboro, Md., promotes technological innovation “to improve the quality, durability, affordability and environmental performance of homes and home-building products,” according to its president, Mike Lozier.

Created in 1964 as an NAHB subsidiary, the center is the industry’s primary source of research and information related to home construction and development issues, and its seal of approval is internationally recognized.

Copyright © 2008 The Orlando Sentinel, Fla., Jerry W. Jackson. Distributed by McClatchy-Tribune Information Services.