Basement extensions: Creating one in the Borough of Camden in 2025
While considering the options for extending your home in Camden, most people consider building outwards or upwards, while these can be excellent solutions, they also come with drawbacks. Extending at ground level often means sacrificing valuable garden space, which is a concern in areas like Primrose Hill, Hampstead, Belsize Park, and St John’s Wood, where gardens are highly valued. Adding a storey above can be complex and subject to planning constraints, particularly in conservation areas. Loft conversions, while popular, aren’t always feasible due to roof structure limitations. In some cases, homeowners have already extended in multiple directions - side, rear, and into the loft, yet still find they need more space.
So what’s the next option? What about adding a basement? Can you build a basement under an existing house? The answer is: sometimes. In this guide, we’ll explain when it’s possible, when it isn’t, and when it’s a smart investment for your home.
Understanding Camden’s Basement Policies
Camden Council has established clear policies shown on their website to manage basement developments under its Local Plan. The council seeks to balance homeowners’ needs for extra space with environmental concerns and the impact on neighbours and streetscapes. They also list out principles in their Camden Planning Guidance 2021 document. The key guidelines include:
Limitations on Depth and Extent – Basements should generally not extend beyond the footprint of the original house, and full garden basements are discouraged. Camden typically permits single-storey basements, though exceptions may be made for larger plots.
Sustainability Requirements – Basement proposals must demonstrate how they address drainage, flooding, and energy efficiency. The council encourages sustainable construction methods to minimise environmental impact.
Impact on Neighbours – Developers must submit a Basement Impact Assessment (BIA) to assess potential effects on neighbouring properties and ground stability. Camden places strong emphasis on structural safety and the cumulative impact of basement developments in certain areas.
Construction Management – Due to the disruption basement excavations can cause, the council requires a robust Construction Management Plan (CMP). This must detail how traffic, noise, and dust will be controlled to minimise disturbance to neighbours.
Flood Risk Considerations – Parts of Camden, particularly near the Regents Canal, may be at risk of surface water flooding. Camden’s planning policy requires detailed flood risk assessments to mitigate this.
What makes a successful basement design?
A well-executed basement should feel like a seamless part of the home rather than a dark, subterranean space. By designing basements that maximise natural light, ensure high-quality finishes, you can make them feel as inviting as any above-ground room.
Key Design Considerations:
Maximising Natural Light – Incorporating light wells, glazed doors, internal courtyards, and skylights ensures that basement spaces feel bright and airy rather than enclosed.
Ceiling Heights and Layout – Generous ceiling heights of at least 2.7m create a sense of openness, while well-planned layouts ensure a logical flow between spaces.
Ventilation and Moisture Control – Mechanical ventilation systems and high-quality waterproofing are crucial for maintaining good air quality and preventing dampness.
Material Palette – Using warm and textured materials such as timber, natural stone, and bespoke joinery can add depth and sophistication to basement interiors.
Acoustic Comfort – Thoughtful insulation and soundproofing prevent noise transfer between floors, making the basement feel like a peaceful retreat rather than a secondary space.
Design ideas for basements under houses
A basement does not need to feel like a compromise - it can be a defining feature of a home when designed with care. Here are some creative and practical ways to make the most of a basement under a house:
1. Luxury Entertainment Space
A basement below the house is an ideal location for warm and inviting cinema room that does not require any natural light.
Image & Design: Nancy Gouldstone Architects
Transform your basement into a home cinema with tiered seating, bespoke acoustic panelling, and soft mood lighting. A high-spec media room can be paired with a bar or wine cellar for the ultimate entertaining space.
2. Elegant Home Office or Library
Basements can be great for cosy home offices
Image & Design: Nancy Gouldstone Architects
With more people working from home, a basement can become a beautifully designed office space featuring built-in bookshelves, deep reading chairs, and a fireplace for warmth. Glazed partitions or internal courtyards can be used to bring in additional light.
3. A Cosy Living Room looking onto a courtyard
Our Belsize Park house created a cosy living room within the basement extension
Pairing your basement space with a lightwell allows for natural light and fresh air - allowing the space to feel similar to the above ground storeys of the house. In our Belsize Park house, we have located the living room on the basement level and created beautiful arched windows and doors that lead onto a small lightwell which allows for views out to the greenery. These rooms can be cosy and quiet and excellent for evening entertaining. In our Belsize Park project we designed a bespoke cocktail bar and positioned a dining table nearby to allow for late night poker sessions and cocktail parties for the parents. While the children can have movie nights with friends.
4. Wellness and Fitness Suite
Adding a gym to the new basement level of your property can give you a really nice space to exercise in
Image & Design: Nancy Gouldstone Architects
A basement is an ideal location for a private gym, yoga studio, or spa area. Infrared saunas, plunge pools, and steam rooms can be incorporated to create a luxury wellness retreat within your own home.
5. Guest or Secondary Living Space
For larger homes, a basement can serve as a self-contained guest suite, complete with a bedroom, en-suite bathroom, and separate entrance. Alternatively, it can be used as an informal family living area or playroom.
6. Art and Music Studios
Soundproofing a basement creates the perfect opportunity for a dedicated creative space. Whether it’s an artist’s studio, a music practice room, or even a photography darkroom, the basement can be tailored to suit artistic pursuits.
7. Utility & Laundry rooms
Basements naturally stay cooler, making them an ideal place for appliances that generate heat, such as dryers and boilers.
A basement utility room can double as a linen store, airing cupboard, or household storage area.
Image & Design: Nancy Gouldstone Architects
A basement utility room enhances convenience, reduces noise, and keeps the rest of the home clutter-free—making it a smart and practical use of basement space.
Basements under gardens
Basements that extend under gardens can offer valuable extra space while preserving the character of a home’s façade. These extensions require sensitive design solutions to ensure light and access are optimised.
1. Light-Filled Garden Rooms
By incorporating large skylights or glass-panelled walkways, a garden basement can feel open and connected to the outdoors. Green roofs or landscaped terraces above can maintain the beauty of the garden while adding insulation and ecological benefits.
2. Hidden Courtyards and Sunken Gardens
A hidden courtyard and sunken garden design by Nancy Gouldstone Architects
Image & Design: Nancy Gouldstone Architects
A sunken courtyard can bring natural light deep into the basement while providing a private outdoor seating area. These spaces can be designed with lush planting, reflective water features, and sculptural elements to create a serene oasis.
3. Pool and Wellness Retreats
A plunge pool and wellness area can be a good way of using a new basement area
Image & Design: Nancy Gouldstone Architects
Basements under gardens allow for the inclusion of swimming pools or spa facilities that seamlessly integrate with outdoor areas. Skylights positioned at ground level can provide dramatic lighting effects and enhance the ambience.
4. Garden-Level Family Spaces
For families, a basement that opens onto a lower garden terrace can create a seamless indoor-outdoor connection. Large sliding glass doors can be used to maximise light and encourage fluid movement between spaces.
Navigating the planning process in the borough of Camden
Pre-Application Advice – Engaging with the council early in the process can provide clarity on likely constraints and requirements.
Basement Impact Assessment (BIA) – This detailed report is often required to address structural, hydrological, and geological risks.
Planning Application Submission – A well-prepared application with clear drawings, environmental reports, and construction management details will improve the chances of approval.
Construction Methodology & Party Wall Agreements – Involving structural engineers and party wall surveyors early ensures the project can proceed smoothly with minimal disputes.
The Cost of Digging a Basement
The cost of a basement extension varies significantly based on factors such as site conditions, design complexity, and the extent of excavation required. In Camden, where regulations are stringent, costs can be higher due to the need for additional planning reports, specialist consultants, and careful construction methodologies.
As a rough guide, excluding VAT:
Basic basement excavation and shell-only construction typically costs £4,000 – £6,000 per square metre.
High-end fit-out, including waterproofing, heating, ventilation, and lighting: £2,500–£4,500 + VAT per square metre.
Total estimated cost (excluding consultants and planning requirements): £6,500–£10,500 + VAT per square metre.
More complex basement projects (such as those requiring extensive and complicated underpinning or piling, deep excavation, or intricate structural work) can exceed £12,000 per square metre.
In addition to construction costs, planning fees, consultant fees, and party wall agreements must be factored in. Working with an experienced architect and a planning consultant from the outset ensures that your basement project is financially and structurally viable from the outset.
How We Can Help
Whether you are considering a basement under your home or garden or another architectural project, our friendly and professional team will guide you through the entire process, from concept design to planning approval and construction management.
Please get in touch we would love to hear from you.