It had started out like any other ordinary weekday afternoon. Christoph Halstenberg was working in his makeshift home office — previously known as the garden shed — and it was raining.
“It was pouring for about two hours,” he said. “I was trapped in the shed until it stopped and when I came out I noticed that there were big puddles everywhere.”
Once back inside the Victorian basement flat, which he had bought a few weeks previously in the summer of 2020, all seemed fine. Halstenberg set about making dinner.
Then he noticed that the floorboards by the stairs made an ominous squishing sound when he walked around. Further investigation revealed they were also soaking wet.
He found, to his horror, that a huge puddle had formed under his bed, and there were pools of water in the living room, too. “The groundwater had breached the slab and was coming up out of the floor,” he said.
Rising flood risk
Global warming is increasing the number of London homes at risk of this kind of destructive flash flooding.
Hundreds of homes in England were evacuated as a result of Storm Henk earlier this month, including in Hackney Wick, east London, where the River Lee burst its banks, flooding 10 acres of land.
Some 1,500 properties were flooded during the wet summer of 2021 and in 2022 the Mayor of London, Sadiq Khan, wrote to 45,000 owners of basement flats to warn them they were at high risk and should keep a “go bag” of warm clothing, medication and important personal documents at hand so they could evacuate quickly if their homes were inundated.
The warning came too late for Halstenberg, who spent the rest of the evening trying to rescue his furniture and possessions, lifting what he could off the ground and on to the kitchen table, bed and kitchen cabinets. Then he spent an uncomfortable night sleeping in the shed.
Being driven out of your home is a stressful experience, but there were two silver linings for Halstenberg.
Not only did a kind friend offer him a spare room (he ended up staying for a year), but he had bought the flat with a plan to renovate and extend it. The rising waters simply added impetus to his plans, and also put flood-proofing the property at the top of his wish list.
‘I was a bit naive’
The result has transformed a grotty one-bedroom basement into a light and spacious two-bedroom home, with an open plan kitchen living room leading out on to a landscaped garden.
The result is not only beautiful but is full of clever ideas designed to protect it from extreme weather — crucial improvements since the National Infrastructure Commission (NIC) calculates that by 2050 more than 600,000 properties in England could be at risk of surface water flooding.
Halstenberg, 48, is a journalist and content creator who moved to London from his native Germany in 2014.
At first he played the renting game, but when the pandemic struck he had plenty of time to think about his living arrangements.
What it cost
- Kentish Town basement flat (bought in 2020): £475,000
- Total project cost: £255,000
- Preliminary investigations: £20,000
- Original size: 750sq ft
- Space added: 375sq ft
He decided that not only would he like to buy a home in London but that he would like a flat he could put his own stamp on, and he really wanted a garden. “I was up for a bit of a project, an adventure,” he said. “I wanted to create a place that really suited me, that I would really love.”
His chosen fixer-upper was a dismal-looking Kentish Town basement flat that cost £475,000. “It was quite run down and very dark, damp and dated,” he said.
But Halstenberg loved its large garden, which would give him plenty of space to extend and upgrade the property.
Halstenberg had a basic homebuyers survey carried out before buying the property. It did mention flood risk but he didn’t see it as an urgent threat. “I suppose I was a bit naive,” he said.
Post-flood fix up
Halstenberg had already hired architect Charles Wu, founder of Polysmiths (polysmiths.com), to renovate his home. “I wanted it to be bigger and brighter, and I then added ‘flood-proof’ to the list,” he said.
Unfortunately for Halstenberg there was a lot of red tape to clamber through before work could start.
As well as the usual planning permission and party wall agreements he had to have a basement impact assessment, plus a survey to make sure there were no buried Second World War bombs in the garden that might be disturbed by his builders.
Happily no ordnance was discovered, but these preliminaries took several months to carry out and cost around £20,000.
Work finally began in the autumn of 2022 and Halstenberg was finally home and dry and able to move back in last summer.
The extension added around 375 sq ft of space to the circa 750 sq ft flat, and the layout has been cleverly rethought by Wu.
A major flaw with the old flat was its complete disconnection from the garden. To get outside Halstenberg had to climb the stairs to ground-floor level and exit through a back door on the landing.
The new extension has glass doors leading straight outside. The space has a subtly industrial vibe thanks to the textured grey Valchromat (wood fibre) panels used to clad the pitched ceiling, the grey-painted exposed steelwork installed to support the property following the removal of an unwanted fireplace, and the slick timber kitchen with its slim, grey ceramic worktop and splashback.
A glamorous new bathroom, lined in black metro tiles and with a mirrored ceiling to give the illusion of height, has been fitted into a corner of the extension, and the former bathroom has been converted into a compact guest room.
Halstenberg’s own green-painted bedroom leads out on to the lightwell, which he is in the process of turning into a courtyard garden. Double doors between the two rooms mean that when not in use by visitors he can enjoy the extra space himself.
Flood-proofing measures
Wu also devised a series of measures aimed at protecting the home from the elements. The flat is on a sloping site, and a section of the garden had to be flattened to make space for the extension.
The mounds of earth removed when digging its foundations were added to the terraced garden — from outside the flat appears sunken into the ground, right up to its window sills.
And all this exposed soil maximises the potential for rainwater to harmlessly soak away. To give Halstenberg the light he wanted, three new skylights have been installed in the roof, all carefully angled to avoid the possibility of rain falling into the room if they are left open.
The interior walls have been limewashed a subtle shade of grey-green. This traditional material adds texture, and it is also breathable. The exterior walls have been tanked, insulated, and treated with a coat of damp-resistant slurry to add another layer of flood protection to the flat.
Outside is the final wall of defence. New channel drains have been dug round the extension, connected to a water pump system that funnels water into the main drainage system during storms. Valves have been fitted to all drainage outlets to reduce the risk of black-flow during flash flooding.
The entire project, including all the red tape, cost £255,000. But since Halstenberg has added about 50 per cent more space to the flat the project has covered its own costs, possibly with a little to spare.
This summer Halstenberg plans to keep working on the garden, training wisteria, jasmine, and clematis to scramble up the timber trellis around the extension so that his home blends even more into the garden.
“It has been a bit daunting but it is exactly what I wanted,” he said. “When I walk in I still feel really happy and grateful.”
How to protect your home from flooding
- Be pre-warned. You can check with the Met Office if you live in a flood-prone area. If you do live in an at-risk area you can sign up for free flood warnings from the Met Office.
- To make your home more resilient to floods you could lay tiles instead of carpet and move electrical sockets up the wall.
- The HomeOwners Alliance (hoa.org.uk) suggests varnishing wooden skirting boards. This isn’t as fail safe as fitting water-resistant plastic skirting boards but is a quick and cheap alternative.
- Another relatively low-cost piece of prevention work is to fit non-return valves on drains and pipes. These will help prevent sewage from flowing back through pipes from toilets and sinks and will cost between £50 and £500.
- Stay up to date with maintenance — make sure your outside walls are in good condition, seal gaps around pipes or wires as they enter your home and keep gutters and downpipes clear.
- If you are seriously concerned you could consider investing in flood protection products like floorboards, which you can fix to your doors and windows, plastic covers to seal air bricks and sandbags or flood bags.
- Make sure your home insurance policies cover flooding and that you have enough cover for a major incident. Take photos of your property and contents now, so you have proof of what it looked like before being flooded.
