British studio Guarnieri Architects has added a glazed box containing a swimming pool, hot tub and steam room to the rear of a Victorian terrace in Clapham Common, south London.

A new floor excavated below the level of the main house provides space for these leisure facilities within the glazed extension, while a mezzanine above hosts a dining area adjoining the kitchen in the original structure.

The transparent walls of the extension flood these areas with natural light, and from the pool provides the residents with a "direct and unbroken visual connection to the outdoors".

Marco Guarnieri and his team worked with structural engineers to find a design for the box that uses as little steel reinforcement as possible, amplifying the weightless appearance of the glass.

To create a "minimal junction" between the two structures, the architects concealed guttering between the glazed box and the existing house.

"The idea was to introduce a structure with sharp geometry, of contemporary look and feel, contrasting in a positive way with the historic fabric of the original house," explained Guarnieri, who founded his eponymous practice in 2004.

"A great deal of attention was paid to the detailing of the structure, in order to achieve a deceptively simple, unobtrusive, minimalist finish."

Inside, dark slate lines the walls of the pool area to create a cavernous appearance, but the material was also chosen by Guarnieri Architects for its low water absorption rate and resistance to algae growth.

The project is named Victorian Remix after its combination of contemporary detailing with the original Victoria-era architecture.

"We like to call our project a Victorian Remix, like a DJ rearranging old records into a contemporary music performance," said the architects.

"We chose the title because it talks not only about the project but also about us. We not only refurbish buildings, we remix them."

The architects also revised the layout of the original house.

Challenged by the five-and-a-half metre width of the property, they relocated staircases to make rooms seem larger and more open-plan, particularly on the ground floor where the rear dining area now flows through to a kitchen at the front of the home.

"The very poor state of repair and the need of a significant upgrade of this Victorian house gave the opportunity to rethink the way an old building may be changed to meet people’s needs in contemporary dwellings," said the architects.

"There is an increased demand in our society focused on well‑being for the introduction of wellness in residential accommodation. This offered the opportunity to rethink, re-lay and remix the spaces of the house," they added.

Excavating basements to allow room for swimming pools and other leisure facilities in London homes has become popular in recent years. Examples include a sunken bathtub below an east London terrace by Studio 304, and  Theis + Khan's addition of a subterranean "cave-like" pool to a Notting Hill residence.

Photography is by Quintin Lake.

Project credits:

Architect: Guarnieri Architects
Structural engineer: Malishev Engineers
Environmental consultant: Alfonso Senatore
Contract administrator: TCL
Contractor: Famella
Specialist glass contractor: Cantifix
Specialist pool contractor: Ocean Pools
AV specialist contractor: Twentytwo Integration