The modular housing industry goes greenBy Tanya M. Williams on 03/16/2006
For decades, modular housing has carried a stigma that’s been hard to shake. Poorly-installed vinyl siding, unimaginative design, over-standardized plans and boring elevations are somewhat to blame as well as an association with mobile homes. While not built to the residential building code’s standards, mobile homes have cast modular homes in a bad light due to thinner walls, substandard windows and other aspects — anything but green. But factory-built homes have come a long way. And the modular concept, desirable in furniture, carpeting and other décor, has become a viable and affordable option for green building.
The potential for modular as an environmentally friendly building practice stems in part from the nature of factory- and systems-built construction. Rather than constructed a stick at a time on site (where building materials are purchased as needed and may be subject to weather conditions), modular homes are constructed in a climate-controlled factory, and materials are purchased in bulk. That saves the manufacturer, the builder and the homeowner money and time. The materials stay dry, which reduces the opportunity for mold growth and indoor-air quality problems. And wastes are minimized because scrap lumber can be used for sills, ledges and other miscellaneous needs.
Doug Williams, director of customer care at R-Anell Homes, a modular manufacturer based in Denver, N.C., says the company’s total waste-disposal costs average $178 a house. That’s roughly equivalent to the hauling and dump charge for a ton of waste. The typical residential project produces three to four times that amount.
In terms of indoor-air quality, modular homes are arguably healthier because the home is framed, insulated, sheetrocked and wrapped indoors. Many manufacturers are moving to formaldehyde-free insulation for the safety of their employees and the benefit of future homeowners. Lumber and other building materials are stored in warehouses and often, due to production volume, used within days of their arrival. Therefore, moisture and humidity have little opportunity to adversely affect the structure. In addition, the homes are generally primed, if not painted, before delivery, which gives any VOCs time to dissipate before the dwelling is occupied. VOCs are organic chemical compounds such as formaldehyde that evaporate from solvents, industrial wastes and other materials.
Another area where modular can be greened is through the comfort systems and building envelope, or exterior shell, of the home. Several modular manufacturers are Energy Star-certified builders and provide features that include 2-by-6 construction, low-e (low-emissivity) windows, increased insulation, house wrap, radiant barrier sheathing, air sealing and other upgrades to improve the home’s performance. Some Energy Star-certified manufacturers will perform a duct blaster test on factory-installed HVAC (heating, ventilation and air-conditioning) systems to ensure the equipment has been installed properly and ducts have been sufficiently sealed and insulated. Periodic blower door tests are also done at the factory to ensure that the process is producing a properly sealed structure.
For eco-conscious builders, the beauty of working with modular is the flexibility and efficiency of the method. Modular homes can be built to order, ranging from a home that arrives nearly move-in ready to one that is virtually a shell, ready for the builder to provide all the interior and exterior finishes. Builders often can negotiate upgrades to allow for raised heels on trusses, engineered roof-framing or use of formaldehyde-free materials. Or builders can opt out of factory features in areas where the manufacturer cannot provide a suitable solution. For example, a builder might choose to do all the flooring and exterior siding on site to allow for the installation of CRI- (Carpet and Rug Institute) certified carpets, bamboo or engineered wood flooring and fiber cement (HardiPlank) siding and trim.
Modular builders are responsible for site preparation and foundation work, so additional measures can be taken before the home arrives to ensure the overall sustainability of the project. For builders striving for NC HealthyBuilt Home (HBH) certification, this includes opportunities such as increasing slab insulation, using solvent-free foundation sealants, increasing fly-ash content in concrete, improving foundation drainage, providing ventilation for radon and other steps that are often just considered good building practices. The HealthyBuilt Home program also credits builders for site opportunities such as protecting pre-existing trees, situating the home for passive-solar heat, employing redundant or improved erosion-control programs, and mulching or milling trees that are removed from the site.
The potential for modular as a viable green-building method has caught the attention of some of the country’s most respected architects and innovative builders. Sarah Susanka, interior designer of “Not So Big House” fame, collaborated with HEED House, LLC of Charlotte to design a modular-format Not So Big Showhouse. West Coast architect Michelle Kaufman has designed two modern, green, modular floor plans — the Glidehouse and Sunset Breezehouse, in conjunction with Sunset Magazine. The modernist architecture magazine Dwell also has produced a line of prefabricated, modular-inspired floor plans and elevations, or “Dwell homes.”
Asheville-based modular builder Innova Homes has teamed with Professional Building Systems of North Carolina to build the first modular house certified as an NC HealthyBuilt Home. A longtime Energy Star-certified builder, Innova Homes pursued HBH certification to see what level of planning, documentation and design modifications would be required to take its homes from Energy Star- to HealthyBuilt Home-certified. The project, a spec home for a client in Columbia, S.C., achieved a silver HBH certification for features such as fiber cement siding, increased insulation, low-e double-glazed windows, a 13 SEER heat pump with three zones of control and independent programmable thermostats, CRI-certified carpets, compact fluorescent lights, low-flow showerheads and a high-efficiency water heater.
Another benefit of modular is its relative affordability compared with stick-built construction. The ability of manufacturers to buy supplies in bulk and have a full-time work force reduces overall costs and quickens the building process. When an order is placed, the home is generally ready to be delivered within four weeks. At this point, the modules are set and, depending on the level of finishing work to be done on site, the home can be move-in ready in as soon as a month, though most projects are finished in two to four months. Stick-built homes often take eight months to a year to finish. The efficiency translates into cost savings, making modular, even green modular, a more affordable option for homeowners. Many local builders of affordable homes have embraced the idea that affordable housing should also be affordable to operate and have incorporated Energy Star into their programs. Energy Star is a prerequisite for the HealthyBuilt Home program. Much of HBH certification is tied to Energy Star certification, so it’s possible to incorporate HBH into affordable housing projects and to bring green building to a broader clientele.