Basement developments are proving an increasingly-popular way of expanding restricted city centre dwellings, as Richard Burton found out.
When Deric and Carla Sydenham found their ideal city centre home, they realised their modest two-up, two-down terrace would need some reconfiguring to accommodate their growing family.
But what they didn't envisage was that the solution to their space problem was literally under their noses.
For the couple had inadvertently bought a house with a basement - something they only discovered by chance when they lifted the floor covering near the porch and found a hatch.
On the other side of it was a dark and uninviting hole. But one with possibilities.
"We literally ripped up some seagrass matting and found it," said Carla, 46. It was dark and gloomy. There were no stairs. It was like something from a horror film.
"We had no reason to believe it was there. A lot of our neighbours' homes had lightwells but ours didn't. It had been covered up by the time we moved in.
"It had been bought by a developer who'd turned it around quickly and sold it on. Before that, it had been a long-term rental so the under-floor potential had never been explored."
With no side access for machinery, turning the dungeon-like hole into something useable meant digging by hand. To make matters worse, the workmen arrived to find the parking bay the couple had earmarked to take a skip had a car parked in it.
"They worked incredibly hard and without complaint," Carla added. "But it was worth it. Some say you never get back the cost of a basement but we didn't care. It just enhanced a house in a really good location. We never wanted a massive house, just one in which we could all have our own space."
The couple live on a quiet street off Alma Road in St Albans, one she describes as "very community-led" and an ideal place for their children, Delphine, ten, and Milo, eight.
The basement was just part of the turnaround project which involved expanding the small bathroom, extending the "basic two-man kitchen" and the loft that needed turning into a room.
All of which was aided by the fact that they didn't have to move out as they merely moved into the basement they didn't know they had. "We slept in bunk beds and on mattresses. It was like living in a Swedish sauna," she said. "But very convenient."
Carla, a buyer for Ocado, and digital production director Deric, 47, are one of the growing number of families digging deep to grow their homes, something that has long been popular in London where the sight of conveyor belts dragging sub-soil up into waiting lorries or the arrival of the tell-tale backhoes and excavators are commonplace.
In fact, Britain saw a 183 per cent increase in planning applications for basement extensions between 2012 and 2017, according to figures prepared by the Halifax which also found that the top 16 local authorities were London boroughs.
Basement specialist Liam Dower whose firm operates throughout London and has, increasingly, been getting projects in Herts, sees a lot of families moving out of the capital and bringing that mindset with them.
"Many people are frustrated by the planning restrictions involved with extending in central London and find they can achieve what they want by going down," he said. "That's something we've been seeing increasingly in Hertfordshire over the past few years.
"We get a lot of inquiries from families and people starting families. They may have an au pair coming and need extra accommodation or just want to create a space for the kids downstairs and get a little separation from the adults upstairs.
"They also like the idea of flexible space, somewhere more functionally diverse. Somewhere they can put in the toys at the beginning and, later, move in a desk and create a study area.
"I had one local client whose kids had recently been on The Voice and he decided he wanted a fully-equipped recording studio where he could really push them."
Liam runs St Albans Basement, the company behind the Sydenham family's project. Like many chartered building firms their range of work begins with the so-called "shell and core" option - typically excavating, reinforcing, damp-proofing and laying the floor screed - to a full fit out.
The latter can mean anything from creating a cinema room to leisure suites with swimming pools and underground car parks.
The company managed to take one period home in Richmond and double its size, thanks to the creation of 100 square metres of subterranean space, which now includes an office, bathroom, media room, playroom, utility room, guest bedroom and an additional storage area.
The eight-month project involved an exacting brief. At the other end of the scale, the owner of a more modest home may not have decided what they want even as the project gets underway.
"A few years ago, basement construction may have conjured images of super-sized swimming pools and underground parking for a fleet of sports cars. The reality today is it's a realistic option for people who love their home, but need more space.
"Our clients' homes are usually in a great location, within the catchment area for the school they want."
"Perhaps within walking distance to the station, the town centre or their favourite local pub," Liam explained.
"If they've extended as far as they are permitted, then the alternative is to go underground to renovate and extend what is already there."
"Sometimes, we have situations where, either through lack of finance or just because they haven't fully made up their mind what they want to do, we are asked to create the shell and then pause for perhaps 18 months before we go back and finish the job.
"It is, on the face of it, quite a tricky operation; digging out and reinforcing the existing foundations even before you start all the internal work. There's a lot of engineering involved and it has to be done in a highly controlled manner.
"The knock-on effect of that of course, is that working in this way also means you get to see a space evolve - from a mass of soil to a very cramped area to eventually quite an amazing space.
"It's often only then that they can start to visualise the possibilities."
One thing we can hope the capital's subterranean living trend doesn't bring are the disputes.
While many new homes these days are created with basements, those looking to expand downwards have publicly fallen out.
And you need look no further than the discord in the pop world when Robbie Williams submitted plans to add two extra floors under his Holland Park pile. His neighbour was Led Zeppelin guitarist Jimmy Page who saw it as anything but a Stairway to Heaven.
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