After a Flood, a Journalist's Dark Basement Flat Was Redesigned to Feel Surprisingly Light — Here's How

"The flat was not in a nice state when I first saw it," explains the architect Charles Wu, founder of the award-winning design practice Polysmiths. "The floorboards had curled out and it smelled of damp — it was a mess."

Just a few weeks after its owner, German journalist Christoph Halstenberg, moved in, a flash flood forced him to move out again. However, this misfortune turned out to be a blessing, because the work needed to transform the dated, gloomy flat into a modern home had to be actioned sooner than originally planned.

"The client bought it thinking he could live there for a bit," explains Charles Wu. When the flood struck, the owner took the opportunity to do a full renovation — and, of course, some essential flood-proofing.

The end result - which included a single-storey extension half-sunk into the garden, bringing lush greenery right up to the windows - is "like being in a hut and living outside," says Charles.

"From wherever you’re standing, you see the garden." Externally, the new extension was wrapped with Siberian larch slats for wisteria to grow around, so that "it would eventually look like part of the garden," says Charles.

Indeed, he named the property Walden, after the book by the 19th-century American naturalist Henry David Thoreau, which documents his two-year experiment living in a cabin in the woods.

Nature has informed the decorative brief, too: "All the materials we used are real and honest — wood, steel, glass. They’re all close to the elements." There’s solid oak wood flooring, pine joinery around the windows, and recycled ashwood boards on the ceiling, plus a natural palette graduating from pale grey in the living area to dark green in the bedrooms.

But perhaps the best natural ingredient here is sunlight. That wasn’t the case initially: "The flat had a deep and narrow floor plan, and is 12 metres from front to back," explains Charles. "So the middle got really dark."

Charles installed a pitched roof with three angled skylights, which pours light "much more deeply into the floor plan," he explains, "but also gives privacy", as previously the neighbours had a direct view into the basement. And around the windowless bathroom in the middle of the floor plan, Charles installed a glass brick screen, "borrowing natural light from the living room."

To ensure that the flat is now flooded with sunlight only, Polysmiths implemented various flood-proofing strategies. For starters, that verdant garden is designed to provide drainage. The builders removed the thick London clay soil surrounding the foundations, and filled the space with topsoil, which "is easier for water to run off," Charles says.

Underground French drains, storm valves and a pump were also laid, to channel excess water towards the sewage system, while external walls were tanked and treated with damp-resistant slurry, then painted with breathable limewash paint, "so that if moisture comes up from the ground, it doesn’t get stuck behind the paint," explains Charles.

The garden was then planted with longer-rooting vegetation to soak up more water. The plants had other jobs too: "We planted things that smelled good, such as roses, lavender, and jasmine," says Charles. "When the client opens the window, his head is at the same level as them." Another thoughtful touch that marks the extent of the flat’s transformation.