Basement Conversion Specialists – London
Transform your unused space into something extraordinary.
At Bigness Group, we specialise in basement conversions that expand your living area and enhance property value. Whether you’re planning a new home cinema, gym, guest suite, or wine cellar, our expert team handles every stage — from design and excavation to waterproofing and finishing.
We deliver functional, safe, and beautifully designed spaces that last.
Types of Basement Conversions
Basement projects vary by structure and client goals. The most common types include:
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Retrofit Conversions – Transforming an existing cellar or storage space into a habitable room.
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New Basement Under Existing Property – Digging below an existing home to create brand-new living space.
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Basement Extension (Under-Garden / Under-House) – Expanding the existing footprint for maximum square footage.
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Semi-Basement Conversions – For properties with partial underground levels or natural slopes.
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Multi-Level Basements – Complex projects for large properties requiring advanced engineering.
Each type requires specialist planning, structural expertise, and drainage systems — all handled in-house by the Bigness team.
Basement Conversion Planning Permission
Not all basement conversions need formal planning permission, but understanding the rules is crucial.
Do I Need Planning Permission for My Basement Conversion?
If your conversion involves major excavation, lightwells, or external alterations, planning permission may be required. Interior-only refurbishments often fall under Permitted Development Rights.
Complex Basement Conversions
Deep basements, multi-level designs, or those under listed buildings require structural assessments, flood risk evaluations, and council approval.
Party Wall Agreements
When working near neighbouring structures, a Party Wall Notice must be served. Bigness Group manages the entire process to ensure full compliance.
Permitted Development Rights
Homeowners may proceed without planning if the works remain internal and do not change the building’s appearance or exceed specific limits. We’ll confirm eligibility during consultation.
Basement Conversion Process
- Consultation & Design – Understanding your goals, lifestyle, and property type.
- Site Survey & Feasibility Study – Structural assessments, drainage, and soil analysis.
- Planning & Permissions – Liaising with architects, engineers, and local authorities.
- Excavation & Waterproofing – Professional dig-out, underpinning, and tanking systems.
- Fit-Out & Finishing – Electrical, plumbing, flooring, and decoration to your specification.
- Inspection & Handover – Final safety checks, certification, and walkthrough.
We manage every phase in-house, ensuring seamless communication and top-tier results.
Why Choose Bigness Group
- Specialists in complex basement and below-ground construction
- Full end-to-end service — from design to completion
- Advanced waterproofing and damp-proof systems
- Expert management of planning, structural, and party wall processes
- Transparent pricing and clear communication
- Guaranteed compliance with UK Building Regulations
Frequently Asked Questions (FAQ)
Q: How long does a basement conversion take?
A: Most projects take between 10–20 weeks, depending on complexity and design.
Q: Will my home be safe during excavation?
A: Yes. All structural works follow strict safety procedures and are overseen by qualified engineers.
Q: Can you handle waterproofing?
A: Absolutely. We install advanced tanking and drainage systems to guarantee a dry, habitable space.
Q: How much does a basement conversion cost?
A: Costs depend on depth, size, and finishes. We provide detailed quotations after the initial survey.
Our Latest Basement Conversion Projects
Discover how we’ve turned dark, unused spaces into bright, modern living areas — from Kensington home gyms to Clapham media rooms and Islington family suites. Each project showcases our craftsmanship, precision, and dedication to detail.
Basement Conversions in London by Borough
We proudly serve clients across all London boroughs, including: Chelsea, Kensington, Westminster, Camden, Islington, Hammersmith, Fulham, Richmond, Wandsworth, and beyond. Our local teams ensure fast response times and expert knowledge of area-specific planning requirements.
Barking and Dagenham / Barnet / Bexley / Brent / Bromley / Camden / Croydon / Ealing / Enfield / Greenwich / Hackney / Hammersmith and Fulham / Haringey / Harrow / Havering / Hillingdon / Hounslow / Islington / Kensington and Chelsea / Kingston upon Thames / Lambeth / Lewisham / Merton / Newham / Redbridge / Richmond upon Thames / Southwark / Sutton / Tower Hamlets / Waltham Forest / Wandsworth / Westminster
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