Behind every historic building development lies …. a lot of engineering!

09 Mar 21

Behind every historic building development lies …. a lot of engineering!

The aspirations of the original owners were pushing the boundaries for the time, but the present owners wanted to develop the historic building to include some more contemporary additions to the property. These included a subterranean structure beneath the existing garden accommodating car parking and recreational area including a swimming pool.

In 1905 department store owner Ernest Ridley Debenham commissioned the architect and designer Halsey Ricardo to erect and decorate a three-storey by five-bay mansion in the Holland Park section of Kensington and Chelsea.

Especially when it involves putting a subterranean structure right next to a Grade 1 Listed building.

Clarkebond were appointed to provide the structural, civil and geotechnical services required for the complex engineering design of the development.

The scheme involved removing the existing south wing swimming pool annex to accommodate a reconfigured and lower level swimming pool and this area was integrated with the existing south wing Orangery and linked to the subterranean rear extension. The car park is accessed via a car lift and a box tunnel constructed beneath the existing Coach House on the north side of the building.

Being Grade I listed the existing building needed to remain intact including its existing foundation formation level. The proximity of the new works to both the south and north ends of the main building required a bespoke solution to maintain the integrity of the main house.

Furthermore, the site constraints, with regards to access/egress also dictated the method of construction. For both these locations a top down construction sequence with plunge columns was chosen. Contiguous mini pored pile walls were installed to both south and north ends.

The capping slabs were then installed and on the south wing excavation beneath the slab progressed from the rear garden with spoil bagged and removed. A raft foundation was then installed, and the adjoining boundary wall underpinned.


On the north end one contiguous piled wall was installed within the existing Coach House and the other adjacent to an existing boundary garden wall. The roof of the tunnel was then installed in coordinated sections to allow the Coach House to be supported off the tunnel roof.

Immediately adjacent to the tunnel was the Grade I listed Garden House. Excavation for the tunnel progressed from the garden and a raft foundation installed to form the floor of the tunnel.

A contiguous mini piled wall was also installed to the perimeter of the subterranean car park/recreational area and to the swimming pool which extended below this area. Being remote from the house this area was constructed in a bottom up sequence.

A drained cavity system was installed throughout. 


Prior to the excavation works commencing the existing building was monitored on all elevations and monitoring was continued for the entire duration of the works with pre-defined trigger level set should the actual movement exceed the predicted movement including differential and tilt movements.  

“This was a fantastic engineering project to work on and technically challenging because of the juxtaposition of Debenham House, a Grade I listed building, to the new subterranean work. Our experience in historic buildings was vital to the success of this project,” states Bill Keane, Clarkebond Director.

A fabulous example of a Grade I Listed Arts and Crafts style house, Debenham House is famous for its green glazed pantile roof and its turquoise, green, and white faience glazed brick exterior walls. The house features a sumptuous Arab-style Hall with a mosaic dome painted by Gaetano Meo, William de Morgan tiles, and painted ceilings by Ernest Gimson. The adjoining Garden House also features tiles by William de Morgan.*

For more information on this project or any other of Clarkebond’s services, please contact

*Debenham House has featured in several films and TV shows including Joseph Losey’s psychological thriller, Secret Ceremony, (1968), which starred Elizabeth Taylor, Mia Farrow and Robert; What the Butler Saw (1990s – TV series); The Wings of the Dove, (1997); Spooks, (2000s – BBC TV series); Agatha Christie: Poirot, (TV series).