It's Prefabulous

LITTLE ROCK — Once upon a time, "prefabricated housing" meant the mail-order kits Sears, Roebuck and Co. sold between 1908 and 1940. Within a few weeks after sending in an order, a new homeowner would receive some 30,000 house parts shipped in two railroad boxcars. All the buyer had to do was haul the pieces to his lot, then put them together.

"Prefab" may also evoke visions of row upon row of the look-alike "little houses made of ticky tacky" of folk song fame, slapped up to fill the post-World War II housing shortage. Or of mobile homes (now renamed "manufactured homes") at the trailer park.

Today's prefabs will instantly obliterate those images, especially a 6,000-square-foot Italian-style villa in Little Rock, one of 25 houses throughout the United States featured in Prefabulous by Sheri Koones (Taunton Press, $25). The prefab elements of the Little Rock house and other houses didn't come as a kit, nor were they made of ticky tacky. And the homes are definitely not mobile.

Prefabulous brings us up to date on today's prefabricated elements and how they are being used in the construction of custom-built houses.

Prefabs are houses and house segments constructed and assembled in a factory and are also called systems-built houses. They continue to include small, relatively low-cost dwellings. But they also include mansions. And now you would find it hard to pick out either kind from among neighboring houses built the conventional way: stick by stick at the site.

Prefab buyers can customize a manufacturer's stock plans or use those penned by their own architects. Styles range from a sleek contemporary California look to a log lodge or the Italian villa-style in Little Rock.

Prefabs can comprise an entire house or certain parts. They can be used when remodeling or adding onto a house. The Little Rock house, built for Max Mehlburger and wife Kaki Hockersmith, used prefabricated structural insulated panels (SIPs), which incorporate framing, sheathing and insulation, for the exterior walls.

WHY CONSIDER PREFAB?

Prefab can be an efficient way to construct a house. Shoes have been mass-produced since 1885 and cars since 1901, while the average new house continues to be stick-built in the same old way, points out the Philadelphia architectural firm Kieran-Timberlake Associates. As a result, productivity in home construction has dropped by 20 percent during the past 30 years while it has risen by 80 percent in virtually every other U.S. industry.

"It's always amazed me that although we'd never agree to have a new car assembled in our driveway or a new dishwasher put together on our kitchen floor, for some reason many of us have no problem assuming that a house assembled on site is going to produce a better quality product than one built in a factory. It just isn't so," writes architect, author and interior designer Sarah Susanka in the Prefabulous foreword.

"With demand increasing for customized designs," Koones writes, "architects along with the industry are pushing the limits of what the public traditionally recognizes as prefab. For the first time, prefab houses are available that have custom floor plans, style and rich detail - benefits not previously associated with prefab construction."

Over the years Mehlburger, a retired lawyer, and Hockersmith, an interior designer whoseprojects have included former President Clinton's Oval Office and the historic restoration of public and private White House rooms, had for years loved and photographed the details of historic Italian villas including chimneys, windows and shutters, floors, roofs, doors, balconies and fountains.

On the structural side, they became interested in using factory-built panels for outside walls. "We looked into it, liked the idea and stayed with it," Mehlburger says. "The more we learned, the more excited we were about it. It just became inevitable."

They presented their architect, John D. Jarrard, with their photographs as well as their wish to use the prefab panels. Jarrard had a few concerns about the SIPs at first, but research showed no problems for other houses built using them.

Bids from several firms led to placing an order for the panels with a Kentucky company, FischerSIPS. The panels were 8 feet wide and 12 feet high for tall ceilings. Fischer estimates that panels cost 5 percent to 7 percent more than for framing, sheathing, insulation and labor for stick-built walls.

These particular panels were almost 9 inches thick and covered with oriented strand board (OSB) - sheets of a plywoodlike product made of wood chips glued together under pressure that are quite dense and strong. The sheets, each 3 /8 inch thick, are glued under pressure to the outside of 8-inch-thick Styrofoam insulation blocks in the factory.

The panels arrived on two 50-foot flatbed trailers. "They were stacked flat just like cordwood, but stacked very high, and that was our house," Mehlburger says, "at least the exterior walls." The panels were numbered at the factory to simplify installation.

The ground floor was ready for the panels. "Imagine now," Mehlburger says. "First you have conventional concrete block foundations, piers and joistsall laid out and decked [over a crawl space]. A 2-by-8 is laid flat around the perimeter of the house and set back just a little."

At the bottom of the panel, the foam ends about 1 1 /2 inches above the OSB sheets. The panel can be set down onto the 2-by-8 plate and nailed into place so that it's standing up.

Along the sides of the panels, the foam ends about 3 /4 inch from the OSBs. A 2-by-8 is slid into the gap. Then the next panelset down onto the perimeter's horizontal 2-by-8, also connecting with the vertical 2-by-8 up the side of the first panel.

Mehlburger emphasized a number of things he and his wife particularly like about the SIPs.

They are two to three times stronger than conventionally built walls, in load-bearing and wind-shear capabilities.

SIPs conserve resources. Some 8,000 pounds of waste is toted to landfills from the construction on one 2,000-squarefoot house, Koones writes. At the factory, any waste is often recycled in energy production or other construction uses. And the OSBs can be made from scrap, not good lumber.

They're more energy efficient. R-value measures the insulating capacity of a material; the higher the number, the greater the capacity. The Little Rock building code requires a minimum of R-18. A 4 1 / 2-inchthick SIP has the equivalent of R-25 when compared to a stickbuilt, insulated wall of the same thickness, says Don Casciola of FischerSIPS. A 6-inch-thick SIP has the equivalent R-value of 38. The Mehlburgers' SIPs are the equivalent of R-46, even before drywall, house wrap and stucco were added.

Air infiltration (how quickly the air inside the house is exchanged for new outdoor air, which then must be heated or cooled) is at least as important as R-value. In a typical stickbuilt house, the air changes 10 to 12 times an hour, Casciola says. Even in a house rated as energy efficient, it can change five times hourly. SIPs createsuch a tight envelope that only 50 percent of the house's air changes each hour.

This means a significantly smaller heating and air-conditioning system is required, although a controlled ventilation system is necessary.

SIPs reduce noise.

SIPs arrive properly aligned because they're made using computer-controlled equipment.

Skilled labor isn't required to install the panels. They weigh about 500 pounds so it can take four men to lift them into place.

SIPs speed construction time because of the all-in-one framing, sheathing and insulation. On the first day of assembling the panels on Mehlburger's house, workers installed 50 feet of wall, even while they were catching on to the process.

Houses built with SIPs largely avoid weather-related disruptions in the construction schedule, or affect the quality of a stick-built house such as dampness that makes wood and drywall susceptible to mold.

You can have the factory cut window and door openings or do it on site. The factory also will ask for specifications on where to cut chases for plumbing and electrical wires.

"I can't remember a problem of any kind [with the SIPs]," Mehlburger says. "It was all straightforward, logical and worked just like it was supposed to. We feel it's a very, very fine way to build a house. Looking for areas where construction could improve, panels would certainly be one thing we should adopt immediately."