They were the talk of the town for years – those massive, often multi-level, underground extensions dug deep beneath London’s most exclusive postcodes, hence the nickname “iceberg” basements.
But then the horror stories began, with tales of neighbouring houses collapsing and outrage over the disruption caused by the creation of subterranean swimming pools and cinemas. So, have these mega-basements now fallen out of fashion, or is there still a whir of construction happening beneath our feet?
The Peak and the Plummet
Well, while basement extensions are still a thing in areas where ground level space is at capacity, the numbers and sheer scale of these types of renovation have dropped dramatically in recent years and there has been a significant decline in planning applications for this kind of build, particularly in the boroughs once at the epicentre of the trend.
The mid-2010s were certainly the heyday of the mega-basement. In 2014 alone, a staggering 842 basement projects were given the green light across London. But by 2020, the landscape had changed dramatically. In Kensington and Chelsea, a borough synonymous with lavish subterranean lairs, planning applications plummeted from 869 in 2014 to just 54 in 2020 – a staggering 93.8% drop. It’s a similar story in Westminster, where applications fell by 92.1% over the same period.
So what put the brakes on the basement boom? To put it simply, a perfect storm of stricter planning regulations, economic uncertainty, and a global pandemic. Many London boroughs, responding to residents’ fury, brought in tougher rules to limit the size and scale of basement developments. By 2015, most had effectively banned multi-storey basements, making the most extravagant ‘iceberg’ homes a thing of the past.
Then came Brexit and the COVID-19 pandemic, which shook up the property market and made many homeowners think twice about major construction projects. The Stamp Duty Holiday in 2020 also played a part, encouraging people to move rather than renovate, as did the surge in construction costs (estimated at 15-20% since 2020) thanks to disrupted supply chains and geopolitical tensions which have pushed up the price of materials such as steel, timber, and cement. A shortage of skilled workers thanks to Brexit has also had a knock-on effect on labour costs.
Where the Basements Are
While the trend has cooled now, thousands of basements were built during the boom years. Between 2008 and 2019, a whopping 7,328 basement projects were approved across the capital. The undisputed king of the basement renovation was the Hammersmith and Fulham Borough, which accounted for 18% of all approvals and 1,337 projects. Kensington and Chelsea (1,152) and Westminster (745) followed closely behind.
These weren’t just extra storage spaces or an occasional guestroom though. A 2018 study by Newcastle University revealed the incredible luxury hidden beneath London’s streets. Among the 4,650 approved basement extensions that they examined, they found 376 swimming pools, 456 cinemas, and almost 1,000 gyms. One particularly opulent example in Holland Park even boasted its own artificial beach.
The Future of the Basement
While the days of the mega-basement seem to be behind us, the desire for more space in a crowded city isn’t going away. Basement extensions are still happening, but they’re more likely to be modest, single-storey additions for growing families rather than extravagant playgrounds for the super-rich. Although with the recent rebound in the property market, some experts are predicting a new wave of basement construction, albeit on a smaller, more sensible scale, particularly with wealth-targeting taxation on the horizon.
So, while you’re less likely to hear about a new underground beach being built in your neighbourhood, the London basement is far from extinct. It’s just become (a little!) more down-to-earth as home renovation trends are shifting towards sustainability focused upgrades such as insulation, triple glazing, solar panels and under-floor heating rather than the ‘bling’ basement extensions which dominated in the 2010s.
