BERLIN — In Berlin, the architectural firm Rundzwei recently completed a residential project called the Korkenzieher Haus, or Corkscrew House. Shaped by strict size regulations, the four-bedroom, four-bath home features a staggered spatial arrangement with a sunken lower level including the master bedroom with direct access to an outdoor lap pool. A sculptural central staircase in timber spirals up through the multiple levels, culminating in a pitched skylight.
Together with these features, the home takes its name from its facade and roof, clad entirely in cork.
“The client wanted to be different,” said Andreas Reeg, a co-principal and co-founder of Rundzwei along with Marc Dufour-Feronce.
The Corkscrew House is among a growing number of projects using cork as a main material. Architects and designers are discovering the many benefits of this material long associated with the wine industry.
The entire exterior of the Korkenzieher Haus, or Corkscrew House, is made of cork. “The client wanted to be different,” said Andreas Reeg of Rundzwei, the architectural firm that designed the residence.CreditGui Rebelo/Gui Rebelo Architecture Photography
“It is a sort of a wonder product in terms of sustainability,” said the architect Tom Surman, a principal and co-founder at the London firm Surman Weston. “Before we researched it, we didn’t realize how sustainable it was.”
The firm designed the Cork Study, a garden studio for a couple in North London that, along with a green roof of wildflowers and a birch plywood interior, is distinguished by its cork-clad exterior. The design was shortlisted for a Royal Institute of British Architects award in 2017. “It can do so much as a building material,” Mr. Surman said of cork. “It offers thermal and acoustic insulation. It’s weatherproof. It’s lightweight.”
The team arrived at the material in their search for an “earthy quality,” Mr. Surman said, that would help the structure blend into its surroundings. As with Rundzwei’s project, it was Surman Weston’s first time working with cork.
“We had never seen it used on a building in the U.K.,” Mr. Surman said. “I remember when we were unpacking it. It was uniform, well made, and the colors were really nice. It looked exactly how we all hoped it would, which was a bit of relief.”
The material was also new for the construction crew, who were equally pleased with how “easy it is to work with,” he said. “It’s soft, easy to cut and handle.”
But the firm was most impressed with its sustainability, as were the clients, the musician Tom Hardy and his partner, the textile artist Jo Gaskell.
“Cork as a building material has much to recommend it,” Mr. Hardy said via email. “It is itself a sustainable material, as trees are not destroyed in its harvesting. It has great insulating properties, both for heat retention — we rarely have to turn on the under-floor heating — and for sound — I use it as a recording studio. It is also aesthetically very pleasing. It has practically a zero carbon footprint.”
Mr. Hardy pointed out that its use in architecture also offers cork manufacturers an alternative market at a time when winemakers are using more twist caps. A natural material that is moisture- and mold-resistant, fire retardant, biodegradable and recyclable, cork is the bark of the cork oak tree. Its first harvest occurs when a tree is 25 years old, and the bark, which is able to regenerate, is then extracted every nine years in a process called stripping.
All cork roads lead to Portugal, which is home to the world’s largest area of cork oak forests, covering around 730,000 hectares, or 1.8 million acres. “Portugal can be proud of being a pioneer in environmental legislation, since the first agrarian laws that protect the cork oak forests appear in the early 13th century,” said Joel Esperança, a co-founder of Contaminar Arquitectos in Leira, Portugal. Not surprisingly, the country also produces half the world’s cork.
To the east of Lisbon, the insulation division of Amorim, a cork production company with a 150-year heritage, supplies most of the world with cork for insulation and facades. Ground into granules, cork is formed into expanded insulation corkboard through heat and pressure that releases the cork’s natural resin — forming the glue that holds the cork together, without additives, in rectangular panels.
The facade version “is manufactured under slightly higher pressure and achieves a smoother and denser surface,” said Mr. Reeg, of Rundzwei.
Contaminar used the material on Cork Hill House, a 650-square-meter, or 7,000-square-foot, home in Leira that was designed to blend into the landscape. “It was the first time that we worked with cork as a skin,” Mr. Esperança said. “It was an interesting experience for the team. The use of a new material with such natural characteristics pleased us, this one typically Portuguese material, with a history of use in construction for acoustic and thermal insulation.”
Challenged to create a “silent house” that didn’t impact the landscape, he said, the team initially intended to the use cork as insulation only. But both client and architect knew immediately after its installation that they also wanted to use the material for the exterior. “The color, the smell, the texture of the cork pleased everyone,” Mr. Esperança said, adding, “It is a material that ages well.”
He said that Contaminar also appreciated cork’s ability to change color with the seasons, though others have pointed out that this was a potential challenge.
Other designers agree, like Diogo Paradinha, a principal of ATKA Arquitectos in Porto, Portugal, which used cork cladding to insulate the master bedroom in a house from noise coming from a nearby school. “It is a product suited for being outside, having great durability and properties that are maintained over time. However, because it is a natural product, it undergoes color changes according to climatic variations.”
“There may be some risk, or unpredictability, of how cork will respond to the passage of time on the same facade,” Mr. Paradinha said. “There may be areas where discoloration is more pronounced than in others, damaging, in theory, the image of a facade that would be expected to age uniformly.”
In Portugal, cork is cheaper than other materials because of its abundance. Elsewhere in Europe, cork can be slightly more expensive, depending on use. “The cost was approximately 30 percent more in comparison to a normal render facade,” said Mr. Reeg, the architect for the Corkscrew House in Berlin. “But that was due to the detailing of the seamless joints and sharp corners. We suspect that a timber facade cladding with those minimalist details would have cost the same.”
Cork flooring or furniture also can offer a distinctive touch to interiors. “I was a bit skeptical about the material in the beginning, but now I really like it,” said Katarina Varsova, an architect at Formafatal in Prague, who designed an apartment there for a young wine lover.
His request for cork floors informed the direction of the design. The apartment features cork pendant lights, a cork stool by Vitra, a cork key holder at the entrance and a bathroom tiled in a cork mosaic. “Cork offers a softness and warmth,” Ms. Varsova said. “A simple, modern look that will still work in five years.”
At the Corkscrew House, where the client’s desire for a monolithic appearance was evident, Mr. Reeg pointed out a small area on the facade they recently opened up to see how the material has been faring against the climate.
“We’ve had a lot of rain, humidity, nasty weather,” he said. “It’s still in good shape.”
