The way Karen Fitzgerald remembers it, she had retreated one evening to the master bedroom upstairs to read because her husband, Bob, had the TV on a bit too loud in the den downstairs. “The bedroom was a big, ugly space, and we knew that. But I was up there and, looking around, I thought, ‘This is like a “before” picture,’ ” Fitzgerald said.

In their 35 years in the brick Cape Cod house in Northwest Washington, Fitzgerald and her family had added on a garage and a garden-view kitchen and breakfast room, all white and glass, a cheerful setting for an accomplished cook and baker. The dining room had a tailored, contemporary look, crowned with a sparkly modern chandelier; the living room was well appointed and large enough for sofas flanking a fireplace and a baby grand piano in one corner. Only the upstairs had been left behind.

Then last year, with six months of consultation and construction, the spacious master suite became an “after” picture.

Much of the perimeter of the room is now lined with custom cabinetry all veneered with elegant sycamore. The wall behind the bed is faced with the pale wood as well, its lively figuring dancing in the light. The paneling behind the bed continues across the ceiling to form a kind of modern canopy. In fact, it’s the focal point of the room.

A small master bathroom has been enlarged, entered through a mirrored-closet dressing room, glamorous to be sure but eminently practical as well. A drab second upstairs bath was also lightened up and given a contemporary look. And all without changing any plumbing or adding one square inch of space.

Fitzgerald, you see, suffered from an unusual condition, especially for Washington homes: The upper floor of the 1952 house simply had too much space. Like many Cape Cods, it is called a one-and-a-half-story house in public records; when built, the upper floor had lower ceilings that sloped attic-style, and dormer windows and had been left virtually unfinished by the builder. Like many homes in this style, the unfinished attic was finished and made into a livable second-story space.

As Bob puts it, “When we moved in, the upper level was two big spaces, running the full depth of the house.” He raises his arm to indicate the two bedrooms where their boys grew up. “We cut one side in half, a room for each of them.” The rooms for the two boys, now grown, still register as large.

Opposite the boys’ rooms, the master bedroom took up the entire space, from the front of the 3,000-square-foot house to the back. Well, “took up” is an exaggeration: The bed floated in the center of the space, and there were a couple of chests of drawers and in one corner a writing desk. As is the case with most dormered Capes, the ceiling sloped along the left and right sides of the house and then angled down toward the rear of the house at the back of the room. The front wall was interrupted by those dormers, making for a busy-feeling room, even with the minimal furniture.

It was an awkward space, to say the least.

Another oddity was an elevator tucked into a rear corner of the bedroom that takes up a 4- by 7-foot space. It was installed by the former owners and not in use. The three-foot-square structure containing the elevator jutted out from the corner of the room, creating yet one more odd angle. “We don’t want to take it out,” Karen says, “just in case we need it someday.” But, she points out, the house has a main-floor bedroom, “so we can ‘age in place’ down there.”

The ground-floor bedroom proved its worth when Karen and Bob decided to tackle the master suite. For that they turned to architect Andreas Charalambous of Forma Design in the District. They had seen a sleek bedroom he had done (in The Washington Post Magazine) and thought he might have their answer.

“At first I really just wanted him to find me a comfortable chair to read in,” Karen says with a laugh. But soon enough, she and her husband were sleeping downstairs while the upstairs was being completely transformed.

Any changes Karen and Bob had made on the main floor of the house had been in keeping with the age and style of its Williamsburg-inspired design, true to the house and to the neighborhood. But Bob points out that there were no moldings or other traditional details to be lost on the upper floor; it was a big, bland space, a blank canvas that could allow the couple to indulge their more contemporary design sensibility. And, with all the elegant wood, the upstairs treatment isn’t all that extreme — it isn’t as if a glass box were plopped atop a center-hall Colonial.

Karen and Bob still don’t quite believe how their room now seems so pulled-together and sleek. One hint is the way Charalambous set about taming that quirky ceiling: He hid most of the roof angles behind the new wood built-ins, which had been made by Art Creations of Manassas.

With all that room to spare, the designer lined the front-to-back wall with those sycamore cabinets and drawers. He aligned the edge of the cabinets at the point where the ceiling begins its slope. Result: one bothersome angle eradicated, swallowed up inside the cabinetry. The wood-paneled canopy over the bed camouflages an even more unfortunate angle.

“Putting the bed and its canopy in the middle of the room draws the eye away from the ceiling angles that still exist,” Charalambous says.

The elevator remains as well, but now the wall in front of it is sycamore-paneled and has glass display shelves. Adjacent to the elevator at the far end of the room, where the ceiling is at its lowest, Charalambous installed upper cabinets and a long desk-height ledge, setting the cozy area off as a computer area. Neither architect nor homeowners discussed cost, but the paneling and cabinetry were clearly the largest part of the six-figure project.

The two bathrooms were brought up to standard without reorganizing, with just refacing. The master bath already had a long vanity with a whole-wall mirror; now the vanity area has the same pale aesthetic (and sycamore) as the bedroom, and the wall is back-painted glass with a large mirrored square and circle above the two sinks. Minimalist “Arch” model faucets come up from the white countertop and form two arcs over the undermount sinks.

A wall had blocked natural light from the shower. Making that a glass wall — and not rearranging the plumbing — meant finding a free-standing shower fixture. Today a tall stainless-steel shower column, also the “Arch” model from upscale Lacava, rises from the floor next to the glass wall, anchored in a most discreet way to the glass. The shower’s white river-rock wall extends beyond the enclosure to the toilet area.

The only Charalambous suggestion that Karen and Bob weren’t sure about was the ebony stain on the oak floors of the bedroom. Today they love the way the pale sycamore is set off by the dark floor, instead of clashing with the honey-oak stain that was there before.

Oh, and Karen finally got her reading chair: a Harry Bertoia Asymmetric Chaise from Knoll. It has odd angles — perhaps a homage to the former bedroom ceiling! — but it is tucked under one of the dormer windows and Karen can now curl up like a kitten and read all she wants.