Tim Vermeulen, left, and Gabriela Sakamota, with one of their dogs, Sugar, relax in the new kitchen of their remodeled midcentury house. (Bill O'Leary/The Washington Post)

Buyers lucky enough to find mid-20th-century modern houses in the tradition-bound Washington area are drawn to their floor-to-ceiling glass, open interiors and indoor-outdoor living. But these unconventional dwellings from the 1950s and ’60s, now considered historic, can pose daunting challenges when it comes to repairs and remodeling.

“They often have flowing spaces and lots of windows — the design that everyone craves these days — so potentially, you can spend less on the renovation,” says Bill Millholland, executive vice president of Case Design/Remodeling in Bethesda. “But the kitchens are often small and need to be opened up, and if the house is a split-level, it can be hard to add onto because you are dealing with half-floors. It’s much easier to mess up this house type than a two-level Colonial.”

On a tour of Holmes Run Acres, a Fairfax County subdivision of 1950s modern homes listed in the National Register of Historic Places, architect Edith MacArthur points to tall, gabled additions and mock Tudor makeovers.

“These renovations are not respectful of the original designs,” says MacArthur, who lives and works in the neighborhood. “The houses are small, so if you make big, insensitive gestures, you can engulf the whole house.”

MacArthur said she was careful to design modest additions to the 1953 home in Holmes Run Acres owned by college administrator Adrienne Sullivan and environmental consultant Neil Sullivan.

The 915-square-foot, two-bedroom house had already been expanded with a master suite in the 1980s before the Sullivans bought the property in 1999. They waited until 2011 to add a new screen porch, a garage and reconfigured entryway with the help of MacArthur.

Earlier this year, the homeowners converted existing space within the 1980s addition into a TV lounge and a more up-to-date master bathroom.

Adrienne Sullivan’s advice to other owners of midcentury modern homes: “Live in the house for a while before renovating, and plan the renovation really well.”

Waiting to save enough money for remodeling may be a necessity, since many midcentury modern homes are more expensive than traditional dwellings. “People who like the design are willing to pay a premium to not live in a Colonial,” says realty agent Michael Shapiro of Long and Foster, who specializes in midcentury properties and runs the Web site Modern Capital DC.

Shapiro says prices for midcentury modern homes have risen as their designs have become more appreciated by younger generations. The average sales price for a midcentury home in the Rock Creek Woods neighborhood of Silver Spring is about $609,000, according to Shapiro. In Alexandria’s Hollin Hills, he says, modern homes average about $752,000, and in Bethesda’s Carderock Springs, they typically sell for about $850,000.

Many of these homes require some type of renovation to achieve today’s comfort and taste levels. “We are seeing a lot of midcentury modern homes now being sold by original or near-original owners or their kids,” Shapiro says. “Many are largely untouched and would benefit from renovations that fit appropriately with the modernist style of the original design.”

Falls Church architect Michael Cook, who has redesigned about 30 midcentury homes, says some renovating buyers are adamant about preserving the vintage architecture, while others want to more radically transform 1950s modern into today’s modern.

Silver Spring homeowners Leonard Roberge, a book editor, and Jennifer Robbins, an environmentalist, deliberately retained the 1950s character of their house while completing several DIY upgrades. The two spent about $15,000 to $20,000 to update the kitchen with new appliances, Ikea cabinets and a linoleum floor but kept the original layout intact.

They repaired and refinished the original pine paneling on the wall dividing the kitchen from the living room and added cork flooring to the basement. “We tried to do things in the spirit of the house,” says Roberge, pointing to a 1950s-style doorknob from Home Depot on a basement door.

A view through the new entryway into the kitchen of Gabriela Sakamota and Tim Vermeulen's remodeled midcentury house. (Bill O'Leary/The Washington Post)

Down the block, attorney Gabriela Sakamoto and artist Tim Vermeulen embraced a more contemporary look in renovating their 1951 home. Their house and the Roberge/Robbins residence started out as identical designs created by architect Charles Goodman, who pioneered modern-style living in 1950s subdivisions such as Hollin Hills and Wheaton’s Hammond Wood.

Sakamoto and Vermeulen bought the two-level dwelling for $570,000 in 2012, after besting 10 other offers, and completed a $200,000 remodel in 2014 under architect Cook’s guidance.

The couple enclosed their front porch to expand their entrance hall, overhauled their kitchen, upgraded bathrooms and dug out part of the basement to enlarge the utility room. “Storage space is a limitation in these houses,” says Vermeulen, who turned one of three bedrooms into a walk-in closet and office.

The homeowners eschewed the more purist approach taken by Roberge and Robbins, and demolished the wall between the living room and kitchen to unite the two spaces. Above the 10-foot-by-3-foot island, a new wood-covered steel beam rests on a steel post to support the roof. “Opening up the kitchen made a huge difference,” Sakamoto says. “We spend most our time hanging out in this space with its tons of light.”

Casement windows in the living space were replaced with more energy-efficient designs, but the bigger, single-pane glass panes in the room still remain. “It was mostly a matter of cost,” says Sakamoto as to why she didn’t replace all the windows.

“Large areas of single-pane glass are the biggest challenge of midcentury houses,” Cook says. Replacing this glazing typically requires expensive custom units, since most standard windows aren’t the right size and have traditional components, such as sashes and divided lights, that look out of place in modern homes.

To upgrade a window wall in a Wheaton midcentury home, Cook estimates the owner would have to spend $2,610, or about $35 per square foot on the glass, frames and installation.

“Windows in these houses are a big deal because they are so important to the modern aesthetic,” says architect David Benton, who works for Rill Architects in Bethesda. “We struggled to get the right look while still being cost-efficient.”

A before photo of David Benton's living room shows the previous location of the sliding glass door. (Courtesy of David Benton)

Wood on the inside of the window frames complements the cedar-clad ceiling and fir beams spanning the living space. (Photo by Michael K. Wilkinson)

Benton and husband Dennis Kirk, an executive coach, replaced the windows in their 1957 home in the District’s Palisades neighborhood with custom, aluminum-framed units, part of a renovation costing about $250,000.

The 4-foot-by-6-foot windows in the living room overlook a new deck and bamboo-planted rear yard. They are double-paned with argon gas filling the space between the glass to create an additional thermal barrier.

Wood on the inside of the window frames complements the cedar-clad ceiling and fir beams spanning the living space. “The wood gives the house a California feeling,” Kirk says.

The homeowners kept the kitchen as a separate room but overhauled the space with new Ikea cabinets, GE appliances and a subway tile backsplash. “We didn’t want an over-the-top, extravagant space but one in keeping with the middle-class roots of the house,” Benton says.

Cook says such small houses built in the 1950s “allowed ordinary families to have affordable modernism” and has no qualms about making them even more modern for today’s families.

Recently, the architect partnered with Shapiro to buy and transform a Goodman-designed house in Alexandria’s Lincolnia Park neighborhood. Now on the market for $875,000, the four-bedroom house combines the original 1951 dwelling and a larger wing. The new addition supplies the types of spaces desired by today’s homebuyers: a two-garage, spacious kitchen and huge master suite with a sitting area, wall of closets and en suite bathroom.

“A lot of people want open, modern houses, but they don’t have millions of dollars to build or buy one,” Cook says. “By renovating midcentury houses and adding on to them, we are creating modern living spaces at a more affordable price.”

Deborah K. Dietsch is a freelance writer.