Reflecting a sea change in Washington area buyers’ priorities, EYA’s Mosaic District townhouse community in Fairfax is unabashedly modern. (Katherine Salant/For The Washington Post)

Long-time observers of the new-home market in the Washington area will tell you that some designs really are “new and original” while others billed as “new” are actually newer versions of floor plans that have appeared again and again.

What accounts for this perennial bestseller category? Do the designs resonate with buyers in some unique way? Are they easier to build? Or priced just right?

When I recently posed these questions to executives at Brookfield Homes and EYA (formerly Eakin/Youngentob Associates), two Washington-area home building firms that have successfully sold the same basic plan for more than 15 years, and to the architects who designed these plans, I learned that the correct answer is “none of the above.”

From a home builder’s perspective, the characteristic that makes a plan a winner is “adaptability.” A plan that is easily adapted to changing buyer priorities without major changes can save a home builder lots of money, said Vienna architect Bill Sutton, the designer of Brookfield’s original 1993 Waverly and all its subsequent iterations.

After a home builder has constructed the same house 10 to 15 times, Sutton said, he knows the cost almost to the penny, and, given the highly competitive nature of the home-building industry in this area, he can lock his subcontractors and suppliers into that pricing structure. Modifying the plan here and there does not drastically affect a builder’s costs. By contrast, when a new design is introduced, all the vendors will seize the opportunity to raise their prices by as much as 10 percent, Sutton said.

Equally endearing to the builders, these cost-saving modifications in some cases can be so deftly executed that most buyers will not realize that they are in the same house.

This is especially true of EYA’s 16- and 18-foot-wide townhouses that debuted as the “Emerson” and the “Fayette” at Alexandria’s Old Town Village in 1996. At that time, they really were “new and original,” combining the pizazz that 1990s buyers prized with an unusual and efficient floor plan: a rear garage accessed from an alley (rare at that time) and three living levels above the ground-floor garage (other builders offered only two).

The main living level on the second floor, however, followed resale dictates with a large formal living/dining area on the front separated by a wall from a smaller, informal eat-in kitchen at the rear. The third floor had two bedrooms, including a large master suite with a dramatic sloped ceiling that rose to a height of about 14 feet. The fourth floor could be used as a home office, an exercise space or a third bedroom when the optional bathroom was added. The usable area occupied only half the building footprint because the sloped ceiling of the master suite below precluded building above it.

Two of EYA’s current versions of these townhouses — the 16-foot, $709,900, 1,620-square-foot Aster and the 18-foot, $809,900, 2,100-square-foot Bryant at the firm’s Mosaic District development in Fairfax — display such a different look and ambiance that only a professional designer would spot the familial connection to Old Town Village.

Reflecting a sea change in buyer priorities, the traditional colonial styling that has been a fixture of the D.C. market for decades has been replaced with a modern industrial look that features brightly colored fiber cement panels, flat roofs and bigger, sleeker windows.

The interiors have been similarly transformed. With formal areas no longer considered essential for resale and most buyers pursuing an increasingly informal lifestyle, the wall between the formal and informal areas on the main living level is gone. The entire floor functions as one living area, enhanced by daylight streaming in from both ends through the bigger windows.

With today’s buyers eschewing drama for function, the sloped ceiling in the third-floor master suite has been flattened so that the fourth floor now fills out the entire building footprint with a 10-foot-deep terrace that extends across the front, a large open “loft” that can be used for entertaining and an optional third bedroom and bath.

The current version of Brookfield’s Waverly is a more nuanced transformation of a single-family house, whose enduring popularity has stemmed in part from the compactness of its plan and a lack of pretension, said Gregg Hughes, Brookfield’s general sales and marketing manager. “It’s not so imposing from the street, and it is larger than it appears to be with a lot more square footage than you sense from the front door,” he said.

First built in 1993 in the Gainesville area of Prince William County, the original Waverly typified the D.C. market with its 2,500-square-foot size and four-bedroom count, but its first floor plan was unusually open with columns and ceiling treatments defining the must-have-for-resale formal living and dining areas on the front. An eat-in kitchen family room ran across the back with a study tucked in between the family room and the garage. The second floor had four bedrooms.

Fast-forward to 2013, and the $495,990 base-priced, 2,590-square-foot Waverly currently offered at Avendale in the Nokesville area of Prince William County is still the same basic four-bedroom house, but the interiors are bathed in sunlight from windows that are about 25 percent bigger and most buyers purchase the optional, $26,000, 4-foot rear extension and a much smaller $8,500 side extension that brings the size to about 3,100 square feet, the current sweet spot for single-family homes in the Washington area, said Dan Fulton, a housing consultant who has studied the D.C. market for more than 20 years.

The added square footage accommodates the different preferences of today’s buyers as well as a new buyer demographic in the Washington area, foreign-born buyers with relatives who regularly visit for several months each year.

On the first floor, the family room is bigger, and the powder room and study morph into a bedroom suite for long-term visitors. The formal dining room is still inviolate, but some buyers have opted to enclose the living room and use it as a home office. The additional area on the second floor expands the master suite and a secondary bedroom and creates an extra room that is finished as a loft for kids’ games and household computer use.

The second-floor loft, which is new for Brookfield, has become an increasingly popular option as buyers now prefer more usable space to the voluminous two-story family rooms and foyers of the 1990s and early 2000s, said Melissa Jonas, a housing consultant with Fairfax-based Metro Study.

Katherine Salant has an architecture degree from Harvard. A native Washingtonian, she grew up in Fairfax County and now lives in Ann Arbor, Mich. If you have questions or column ideas, she can be contacted at or .