Basement Conversions in London

ONYX Basement Services – Basement & Cellar Conversions in London

At ONYX Basement Services, we specialise in basement conversions and cellar conversions in London, turning underused, damp spaces into warm, dry, and functional rooms you’ll love. Our expert team brings years of experience in basement waterproofing, structural repairs, and full below-ground refurbishments. Whether you dream of a home office, gym, guest suite, wine cellar, or high-quality storage area, we provide tailored solutions to maximise your property’s potential.

We start every project with a detailed survey to identify water ingress risks, structural issues, and design opportunities. Our bespoke conversion plans ensure your new basement space is protected for decades. Our services include:

• Cavity Drainage Membranes (Type C Systems) – An internal waterproofing solution that manages and redirects moisture away from your living space.

• External Waterproof Membranes (Type A Systems) – A protective barrier applied to exterior walls to stop water entering from the outside.

• Cementitious Tanking Systems – A robust, seamless coating that creates a watertight seal on walls and floors.

• Deck & Buried Roof Waterproofing – Preventing leaks in balconies, terraces, and flat roofs situated above basement rooms.

• Concrete Repairs – Restoring and reinforcing damaged or weakened structural elements.

Our London-based team combines technical skill with creative vision, using high-quality materials and proven methods to ensure your basement stays dry, healthy, and compliant with building regulations. From compact cellar upgrades to large-scale basement renovations, we manage every stage — design, waterproofing, construction, and finishing touches.

Homeowners across London choose us for our reliability, attention to detail, and clear communication. We’re known for working efficiently in challenging spaces, completing projects on schedule, and minimising disruption to your home or business.

A well-executed basement conversion in London not only adds valuable living space but can also significantly increase your property’s value. With ONYX Basement Services, you’ll benefit from a beautiful, functional extension of your home that’s built to withstand London’s challenging ground conditions.

Basement Conversions in London. Onyx Basement Services also provides expert servicing and maintenance for a wide range of packaged pump systems.

Contact ONYX Basement Services today to arrange your consultation. Let us help you design and build a basement or cellar conversion that’s dry, comfortable, and a true asset to your property.