Under Construction: Peer into the Hole Which Became a Luxury London Double Basement

Wednesday, January 16, 2019

Double basement excavation in London

Our St. John’s Wood Iceberg Mansion is the largest new home we’ve built in London, thanks to its two storey full-size basement. While our portfolio photos show off its finished beauty, the best way to appreciate the scale of the project is to see how it began life; as a vast, steel-flanked hole as deep as a house.

Piling on the pressure

Piling (the process of drilling holes deep into foundational soil into which concrete is poured to form a solid structure) was being carried out just 1.5 metres from the neighbouring home at an astonishing depth of 25 metres. The photo below shows just how cheek-to-jowl we had to work.

Excavation an iceberg basement in London

It was a nail-biting process, but thanks to the world class structural engineers at Elite Designers, a piling contractor who could drill with tolerances of 100mm and our trusted team of contractors from Galower Build, the project was completed without a single crack in the neighbour’s wall.

After piling was complete, we could safely excavate. This is when the clients visited the site and realised they had not just commissioned a home but an incredible feat of technical engineering. 35 lorries a day were being filled with soil, right beside the Abbey Road crossing where the Beatles took their iconic photo.

From the outside the site looked hectic, with diggers, cranes, contractors and daily checks from neighbours, council officers and Building Control. But on closer inspection you would discover that site foreman Terry Totts was running a well-oiled machine, where every action was performed to the minute.

A delicate excavation

Terry’s logistical skills can’t be understated. The site was surrounded by trees with protection orders, so the cranes had to be dismantled and rebuilt in order to be able to pass under their canopies.

These cranes then delicately lowered 20m long, 5 ton red steel beams in place to form temporary structures which would stop the sides of the excavation from collapsing inwards.

Double basement being built in St John's Wood

The large digger above appears to teeter precariously over the edge, but it’s held in place with a counterweight. The smaller diggers that trundled around within the excavation had to be lowered down and removed by crane.

Throughout the photos you can see the rows exposed concrete piles that were carefully dug out. Once fully exposed, these piles were covered by a steel cage and then sprayed with concrete to form a smooth, solid wall.

After we completed the wall of the first basement storey we started digging out the second, as you can see in the photo below, taken a month later when the piles had just been revealed.

Excavation an iceberg basement in London

Despite the scale of the undertaking, the colossal double basement was completed without a hitch. We work with health and safety specialists to plan out the project with minimal risk to anyone on site, while also making sure the client is protected if an accident did happen.

If you want to see what how the project turned out, click here to take a tour of the St. John’s Wood Iceberg Mansion with Senior Associate Michael Gwynn.