We hadn’t been inside the West Virginia cabin for more than 15 minutes when my friend Jane pulled a 25-foot tape measure out of her purse and began measuring. Okay, the place was about 16 feet wide. Length? Well, two 25-foot lengths plus the hallway and then the bedroom for a total of 64 feet. A wide deck ran the length of the open-plan living-dining-kitchen, offering views of green, green, green. Inside and out, the place was modern, lined with white walls, lots of glass, and dotted with iconic bits of midcentury-modern furniture.

Jane was excited by the cabin because the structure was prefab, and she has a nice lot looking onto the Chesapeake Bay. Right now it’s topped by her childhood summer cabin. But might it be nice, she wondered, to replace it, or augment it, with a nice modern prefab structure?

By now it’s fair to say most people do not confuse prefab houses with mobile homes. Prefab is simply a different system for building a regular house, of almost any style, producing it in either modules or panels in a factory. With modular houses, there’s a lot of extra engineering involved: After all, at the factory and at the homesite, pieces of the structure have to be picked up by a crane and set in place, first on the delivery rig and then on a concrete foundation — and in between they bounce around for miles on a truck. (Don’t try this with your typical brick colonial.) With panelized construction, sections of walls, complete with innards such as electrical wires, are stacked on trucks, then linked together on site. Look around the Washington area and you’ll see prefabs, except of course you won’t, because when finished they look like regular houses.

People do, however, continue to equate prefab with cheap, or at least considerably cheaper than traditional “stick-built” construction. But there is a wide spectrum of prefab houses and the companies that make them.

At one end you have factories that spit out econoboxes that, despite their superior engineering, can resemble shipping containers. They include the one bedroom, one bath “i-house” by Tennessee-based Clayton Homes, which can be had for a base price of $75,812. Adding upgraded flooring and appliances takes it to about $85,000 including delivery, or about $117 per square foot. ECO-Cottages by Nationwide Homes of Martinsville, Va., offers a 513-square-foot, one-bedroom, one-bath “Osprey” cottage starting at $59,500, or $116 per square foot. But remember: Prefab prices do not include the cost of the land or the foundation or any necessary site-prep work.

At the other end of the cost spectrum are firms like California-based LivingHomes, which offers high-style contemporary designs at square-foot costs that range from $220 to $250, and much more for custom designs. That doesn’t even include design fees. What you’re getting, the company says, is a soaring architect-designed house — steel frame, lots of glass — for 20 to 40 percent less than a similar house would cost if it were site-built.

Compare these numbers with a 2,200-square-foot house currently offered by Ryan Homes in Clinton, Md. — $121 per square foot including the land it sits on — and the decision to go prefab is not as clear cut as it may seem.

The West Virginia cabin we were visiting belongs to Chris Brown and his wife, Sarah Johnson. Both graduated from Georgetown, where Johnson’s dad, Tony Johnson, coaches the men’s crew team.

While the cabin was being built, Brown fed the fantasies of prospective prefabbers by maintaining a construction blog. Even better, he published his estimates of what he thought things were going to cost and then the real dollar amount.

Soon after we arrived, Jane and I huddled over her laptop reading the blog. (The Brown-Johnson cabin, called Lost River Modern, has WiFi in addition to satellite television.) When we saw the staggering $356,000 total to build the very nice two-story three-bedroom, two-bathroom 2,048-square-foot house in far-out West Virginia, Jane began revising her expansion fantasy.

The cabin is part of a mini-slice of the prefab world: stylish, higher-end houses designed by architects interested in homes that are built in a way that’s more labor and energy efficient and less wasteful than site-built houses.

Brown and Johnson had already been thinking about a getaway house that they would frequently rent out when they saw the winner of the 2003 Dwell Magazine prefab-house competition. The magazine, which covers the world of hip modern architecture, had invited 16 architects and designers to come up with an innovative prefabricated house for $200,000, one more effort to stoke the fire under prefab, which is always threatening to peter out in the face of market realities.

The Dwell competition winner was Resolution: 4 Architecture of New York, and Brown approached principal Joe Tanney in the summer of 2006 when the architect spoke at the National Building Museum. Where some prefab designers think in terms of cubes and at least one thinks in terms of triangles, Res4 thinks about “bars,” long or short sections that can be stacked or angled or cantilevered to achieve interesting effects. “I asked him how efficiently they could do a modest — modest for them — project,” Brown says. “They seemed interested.”

Res4 had a new relationship with a builder, Simplex Industries of Scranton, Pa. Designing a prefab house, it turns out, means nothing without access to a factory that can construct it. Architects don’t own factories, as a rule, and mass-production factories are not necessarily disposed to interrupting their assembly line for a small project.

With contemporary design there’s an additional challenge: The architect or the owner has to find a modular construction company that is attentive to finishes. “With modern,” Brown says, “you can’t hide everything with molding like in traditional-style modular houses.”

David Boniello, vice president for marketing and development at Simplex, says “a lot of thought goes into a room” by Res4 and other design firms. That leads to challenges for a manufacturer. “These guys are architects. They want 52 3 / 8,” not just 53 inches. Also, contemporary architects design a lot of large floor-to-ceiling openings to make place for glass, and those pieces can be tricky to transport, Boniello said.

An advantage of prefab is supposed to be the time savings, and it’s true that the factory can start on the component parts of the house while a crew is still pouring the foundation, something that’s of course not possible with site-built construction. But tweaking machinery and refining designs still takes time. Brown estimates the house was “in the factory” for a year. That gave him and his wife time to buy 30 acres of hillside in West Virginia. Another year was spent after delivery, finishing details such assome complicated flashing for the Charles Goodman-style “butterfly” roof and the interior, with Brown and his brother-in-law providing a lot of the labor. (They also applied the exterior cedar siding and built the deck themselves, then tackled the interior of the lower level, even building the staircase and tiling the bathroom there.)

Brown, who was an attorney but is now a graduate student in English literature, said the “real advantage” was that he and Johnson, a nurse at Children’s Medical Center, “didn’t have to manage a building site” that was almost three hours from their home in University Park, Md.

Without the land cost or the excavation or the $12,000 they paid to put a road up the side of their hill, Brown and Johnson calculate their square-foot cost as $150 to $160, “the low end of prefab,” Brown said. At least of “architect prefab.”

Res4 and Simplex’s attention to detail shows up in an interesting way in the Lost River Modern cabin. The 16-by-64-foot modular level made by Simplex rests atop a walk-out basement foundation, made on site by a local contractor and still being finished by Brown and his brother-in-law. The difference between the two levels is in the details, but they add up. Upstairs the light switches all have dimmers, the floor is bamboo, pocket doors are frosted glass in a light-wood frame, built-in kitchen and bedroom cabinetry is precise and the ceramic-tile bathroom, delivered on a truck, is in perfect condition. Aside from the Res4-specified windows and doors, the downstairs might be called “builder grade”: light switches are simple toggles, the floor is polished concrete (and cracked), the bathroom has caulking and grout problems and some gapping where the walls meet the floor (probably settling, Brown guesses). Upstairs, the closets have nicely engineered, close-fitting doors. Downstairs the closet doors are, well, a work in progress.

One thing Brown and Johnson’s Lost River Modern cabin has in common with several other prefab properties is that it can be rented, by people who want to check out a modular house or just want a West Virginia getaway. Rent for the Lost River Modern cabin starts at $250 a night, usually with a two-night minimum. Method Homes’s 1,811-square-foot Method Cabin 1 (base model $271,650 and higher) at Mt. Baker in Washington state, rents for $250 to $300 a night. The owners of a weeHouse by Alchemy Architects of Minneapolis, located on the Oregon coast rents from $225 to $275 a night (oceansideprefab.com).

One thing Brown and Johnson probably don’t have in common with those other prefab owners: They have four children. “Twice as many kids as when we started out,” Brown adds.

As for Jane, she’s still thinking about it.