St John’s Wood Basement
This project, currently in the construction phase, is a refurbishment and basement extension that transforms a mid-19th-century semi-detached villa in the St John’s Wood Conservation Area, Westminster.
Designed as a long-term family home, the scheme enhances day-to-day living while preserving the character of the original house and responding sensitively to its conservation area setting. The project is a sustainable refurbishment, with internal insulation, high-performance windows, an air source heat pump and mechanical ventilation with heat recovery.
Delivering the basement required a highly coordinated and technically demanding construction process. The planning application included a Basement Impact Assessment and detailed soil investigation studies, while a comprehensive Party Wall process included movement monitoring during the structural works. more
Designed as a long-term family home, the scheme enhances day-to-day living while preserving the character of the original house and responding sensitively to its conservation area setting. The project is a sustainable refurbishment, with internal insulation, high-performance windows, an air source heat pump and mechanical ventilation with heat recovery.
Basement extension
The basement extension adds two ensuite guest bedrooms, a cinema room, a gym and a new spa bathroom. Front and rear lightwells bring natural daylight into the basement, creating bright, welcoming spaces that feel connected to the rest of the home. A walk-on rooflight in the rear bedroom further improves light levels and strengthens the sense of openness below ground.Delivering the basement required a highly coordinated and technically demanding construction process. The planning application included a Basement Impact Assessment and detailed soil investigation studies, while a comprehensive Party Wall process included movement monitoring during the structural works. more
Underpinning to the existing building was carried out in a hit-and-miss sequence, and temporary support steelwork exceeded the amount of permanent steel used in the finished structure. Close coordination between structure, drainage, below-ground drainage, MVHR and architectural elements was essential to ensure the building performs efficiently as a whole.
Rear and side extensions
At ground floor level, rear and side extensions create generous new living spaces, together with a home office that can also function as a flexible third guest bedroom. Large sliding doors open the rear of the house to a newly landscaped garden, improving the relationship between inside and outside and making the rear elevation feel more expansive and light-filled.Sustainability
Sustainability is central to the project. The house has been comprehensively upgraded with improved insulation, airtightness measures and a low-carbon heating strategy based on an air source heat pump. Mechanical ventilation with heat recovery supports comfort and energy efficiency throughout the house.Where space is limited, high-performance materials such as aerogel are used, while natural materials including woodfibre, cork, lime plaster and clay paint help create a healthier and more breathable internal environment. Existing sash windows are being reglazed with vacuum glazing, while all new windows and rooflights are triple glazed.
The project also incorporates a range of passive environmental measures. External shutters to rooflights, internal blinds to heritage windows and woodfibre insulation to the existing roof help reduce overheating risk. A wildflower green roof, pebbled blue roof and rainwater harvesting tank contribute to the Sustainable Drainage Strategy for the site, supporting biodiversity and managing surface water more responsibly.
Materiality
The final material palette reinforces the project’s balance of conservation and contemporary design. Reclaimed London Stock brick, including material sourced directly from the site, is reused in the new external walls, complemented by Porphyry stone detailing.Thin metal-framed glazing and lightweight metal balustrades provide a refined contrast to the heavier masonry elements. Portland Stone is specified throughout the lower ground floor and for the basement stair.
Are you interested in a St John’s Wood basement extension or a deep retrofit for your own home? Contact us to discuss how we can help transform your property with thoughtful design, technical expertise and a tailored approach.
Project details
Project Architect:Karolina Banasik
Contractor:
Harris Calnan
Structural Engineer:
Richard Tant Associates
Project Type:
Basement extension in a conservation area
Location:
Springfield Road, St John’s Wood, NW8
Videography:
Harris Calnan
