A GLASS staircase can be a glittering piece of architectural sculpture, a light well for an entire house and a signifier of openness.

It can also be scary.

Kersti Urvois learned that three years ago during a cocktail party at the home she and her husband, Louis, own in Kensington.

Mrs. Urvois, who owns the British franchise for Casa Decor, a Spanish company that creates architectural exhibitions, guided a group of guests up the two-story glass staircase that runs from the first to the third floors at the center of the 5,500-square-foot home.

Twenty went up.

Only 19 came down.

“I realized that one guest was missing, but she hadn’t called for help,” said Mrs. Urvois, 61. “I thought she was looking at something.”

Mrs. Urvois found her upstairs, a glass of Champagne in one hand, her shoes in the other, too afraid to walk back down the glass stairs. With the help of two men, one walking in front and one behind, she was able to descend.

“Everybody, the first time, is scared,” said Mr. Urvois, 67, the former chief executive of Loewe, the Spanish luxury goods company.

Everybody, that is, but him.

On a recent spring day, he bounded up the staircase, from his office on the second floor, to the top like a teenager.

“I’m a mountaineer, so this is nothing,” he added, peering from the third-floor landing down to the first floor. He pressed a button and the glass pane of a skylight positioned over the staircase slid slowly into its pocket in the roof, opening to allow fresh, damp air into the house.

The staircase and the skylight are the work of Rick Mather, an American architect based in London, who designed the renovation of the freestanding house, which the couple bought for $4 million in 1997. The work took two years and cost $2 million, they said.

In the renovation, Mr. Mather used the glass staircase to transform a dark Victorian structure into one filled with light, even on a gray day. It was such a success that when one of Mr. Mather’s staff architects who briefly worked on the Urvois house, Luis Treviño Fernandez, and his partner gutted and renovated their London home in 2005, they followed suit, adding light with their own glass staircase and skylights.

In both houses, the glass staircases help to overcome the limits of the original structures. “It was a way of addressing the drawbacks of Victorian homes with their long corridors,” Mr. Urvois said. “Instead of the house being dark and gray and sad in atmosphere, we now have light and a joyful atmosphere.”

Mr. Mather said he was drawn to the way glass could brighten a space without calling attention to itself. “I like the ambiguity of it, I like that it brings in light, and I like that it disappears,” Mr. Mather said. “I like to not show how it’s supported.” The staircase treads are made of two layers of tempered glass, each two-thirds of an inch thick, which have been laminated together with silicon elastomer, an adhesive, said Mr. Treviño.

Each tread has three sand-blasted, textured, non-slippery grooves. “If you slip, the groove will stop you from slipping,” Mr. Mather said. And each tread rests on four steel pads, which are welded to steel stringers, the support structure hidden in the walls that surround the staircase. The balustrades that support the treads are also made from tempered glass, and a steel banister provides more security.

The glass for the staircase is heated to 1,200 degrees Fahrenheit and then cold air is blown over the surface, causing the outside layer of glass to set while the core is still cooling and shrinking. The process increases the strength of the glass six-fold, said Tim Macfarlane, a structural engineer at Dewhurst Macfarlane & Partners in London, who collaborated with Mr. Mather on the design of the house, allowing the treads to support a 300-pound person. And when tempered glass breaks, it shatters into tiny pieces, instead of dangerous shards.

(In Britain, a single tread has to consist of two layers of tempered glass laminated together, and a one-by-three-foot tread costs about $300, uninstalled, Mr. Treviño said. In the United States, safety standards require that a glass tread consist of three layers: two of tempered glass laminated together, with a third, laminated top layer of tempered glass or another material. The price for the same size tread is about $450 to $700, uninstalled, said David Ling, a Manhattan architect.)

When Mr. Treviño, 37, and his partner, Alexander Skinner, 32, decided to renovate their house, a three-story 1890s Victorian, Mr. Treviño, too, turned to glass to fill the house with light.

The couple, who met as graduate students at Harvard, paid $1 million for a 1,200-square-foot house in the Wandsworth neighborhood of southwest London, where Mr. Skinner, an analyst at the Department for Environment, Food and Rural Affairs in the British government, had grown up. Mr. Treviño wanted to insert a skylight above a glass staircase. In the rear of the house, he planned to rip out the exterior wall and part of the roof, replacing them with glass, and widen the house by five and a half feet. He designed a cardboard model, and showed it to his partner.

Mr. Skinner was not moved.

“I said, Show me,” Mr. Skinner said. “I need to see it in scale.”

On a warm summer day, they biked to the Urvois house. As Mr. Skinner stood on the glowing glass staircase, looking up to the skylight, he said, “I was convinced.”

In their home, the two men made design choices to fit the way they live. Both love to cook — Mr. Treviño the savory part of a dinner, Mr. Skinner the desserts — so the kitchen was important.

“Alex was into the physical details, and shapes and form, like a counter where he could plug in a mixer,” Mr. Treviño said. Mr. Skinner added: “I wanted a place to put my computer that wasn’t on the dining table. I wanted visible plugs, I wanted a place for the blender.”

In their $600,000 renovation, they opened up the inside of the house, bringing in light through the skylight and the staircase (the treads are identical to those at the Urvois house), as well as through two exterior glass walls and the roof at the rear of the house.

The first floor flows from the living room into the kitchen, the center of the house. The kitchen feels both sleek, with basalt stone counters, and joyous, because it is so open. Light floods in from the glass ceiling and the glass walls, one at the rear facing the garden and one on the side.

On the second floor, Mr. Treviño designed a guest bedroom and bathroom, and a few steps up from that, an office for Mr. Skinner and a library for himself, where he can read, listen to music or draw.

The master bedroom and bath are on the third floor, where skylights filter light into the bedroom. The shower has a one-way glass window, allowing a view of the garden as well as privacy.

Above the staircase, Mr. Treviño inserted an L-shaped piece of glass, forming a skylight and, at a right angle to it, a window.

“What the renovation, the light, has done, is make this a warm, happier place,” Mr. Skinner said. “And the staircase made a big difference.”

Source: New York Times – U.S.A.