Basement Conversion
Look down. The most valuable, untapped potential in your London home is right beneath your feet. At Reltic BIM, we are a specialist London basement company and Design & Build experts, transforming damp, forgotten cellars into stunning, high-value subterranean living spaces.
We blend intelligent structural engineering with a seamless construction process for every basement conversion, all powered by advanced BIM technology. This allows you to step into and perfect your new subterranean retreat in virtual reality before we begin excavation. Let’s turn your unused cellar into a spectacular new floor of your home.
Investment & Lifestyle
A Foundation for Value: The Case for a London Basement Conversion
Creating an entire new floor beneath your home is a feat of engineering and a powerful financial strategy. A professional cellar conversion offers a unique combination of benefits that other forms of home improvement cannot match.
A professionally engineered basement conversion is one of London's most significant value-adding home improvements, delivering an exceptional return on your investment upon resale.
A modern basement refurbishment creates the perfect blank canvas for rooms that benefit from privacy and light control. Whether you dream of a home cinema, a private gym, or a bespoke wine cellar, a luxury basement provides unparalleled flexibility.
Add an entire new level to your home without sacrificing a single inch of your garden. A London basement conversion is the ideal solution for properties where a ground-floor extension isn't feasible, preserving your vital outdoor space.
The underpinning process required for most basement construction projects intrinsically strengthens your home's existing foundations, providing long-term structural benefits and peace of mind.
Why Choose Reltic BIM?
Our Basement Approach
Creating a luxury subterranean space beneath a London home is a feat of advanced engineering. At Reltic BIM, we specialise in the art and science of basement conversions. Our unique Design & Build process combines meticulous structural planning with a commitment to absolute transparency, transforming challenging groundwork into an exceptional new asset for your home.
Precision is paramount in subterranean construction. We build every project twice: first, as a perfect digital replica using Building Information Modelling (BIM), and then in reality. This „digital twin” allows our engineers to stress-test every structural element and perfect the waterproofing strategy, ensuring full compliance and eliminating risks before we ever break ground.
A complex project demands simple, clear communication. We provide a single point of accountability through a dedicated Project Manager who oversees every detail. Our commitment is to a truly turnkey service, defined by a fixed-price contract that will not change, and a detailed project schedule. Your 24/7 access to our client portal ensures you are always informed and in control.
Our methodology provides four key guarantees:
- Explore your future space with an interactive 3D model.
- Resolve all structural conflicts before work begins.
- Ensure total budget efficiency with precise material planning.
- Certainty with a fixed-price contract and a detailed schedule.
A Guide to conversions
Basement Conversion Types
A successful London basement conversion is a testament to meticulous planning and expert engineering. As leading basement specialists, we have mastered every type of subterranean construction.
Cellar Transformation
This type of project focuses on upgrading an existing cellar or vault into a modern, fully habitable, dry, and warm living area, referred to as a cellar conversion.
Perfect for: Properties with an existing cellar that has adequate headroom but requires a full basement renovation and professional basement waterproofing to become truly usable.
Expert Insight: The absolute key to success is a guaranteed waterproofing system. We install robust cavity drain membranes to create a permanently dry environment for your basement, backed by a full insurance guarantee.
Full Basement Excavation
The most ambitious undertaking, this involves creating a brand-new basement level beneath a house where no cellar existed before. This is the ultimate basement dig-out.
Perfect for: Adding maximum square footage in high-value London postcodes. This type of basement construction offers the greatest potential for creating expansive new living areas.
Expert Insight: This major engineering project requires Full Planning Permission and deep expertise. Our BIM process is critical for planning every stage of the basement excavation with millimetre-perfect precision.
Creating Headroom
For cellars with low ceilings, we increase the head height by digging down and extending the home’s foundations through a process called structural underpinning.
Perfect for: Transforming a cramped cellar into a magnificent, full-height living space. This is a common and highly effective type of basement conversion project in London.
Expert Insight: This is a highly technical structural project, requiring detailed engineering calculations and Party Wall agreements. Our integrated Design & Build service manages this complexity seamlessly for you.
Lightwells & Sunken Gardens
These projects are designed to pull natural daylight deep into the new subterranean level, often involving excavation work in the garden. This improves well-being and the quality of the new environment.
Perfect for: Creating bright, airy luxury basements that defy expectations, using striking features like walk-on structural glass and sunken garden patios.
Expert Insight: Any external alterations, including new lightwells, will require Planning Permission. A well-designed lightwell becomes a stunning architectural feature for your amazing basement conversion project.
Our Technology & Your Benefits
Clarity, Certainty & Control
Our entire philosophy is built on mitigating risk and delivering certainty. This is achieved through our „digital-first” approach. Advanced BIM technology allows us to model every structural beam and waterproof membrane before we break ground, eliminating on-site errors. This precision translates into a predictable, fixed-price budget and a clear timeline, managed through a seamless process which is the foundation of every successful basement conversion project.
Our Process
Our Turnkey Basement Conversion Process
Our workflow for London basement conversions is designed to be transparent, collaborative, and efficient, giving you complete oversight without the stress.
Step 1
Consultation & Feasibility
Every subterranean project begins with a thorough feasibility study. We analyse ground conditions and structural suitability, providing clear advice on the planning permission for your basement.
Step 2
Digital Survey & 3D Model Creation
Our surveyors conduct a precise digital scan of your property. This data forms the bedrock of an intelligent 3D BIM model, ensuring every decision in your basement design is based on flawless accuracy.
Step 3
Interactive 3D Design
This is the creative heart of the project. We translate your vision into tangible architectural designs and invite you to take an immersive 3D tour of your proposed basement to perfect its layout and feel.
Step 4
Planning & Permits
Our in-house experts manage the entire planning application. In parallel, we develop the complex structural engineering and basement waterproofing designs required for Building Control approval.
Step 5
Final Plan & Fixed Quote
With all approvals in place, we present you with a comprehensive, fixed-price quote for the entire build. This is your guarantee against budget creep for your basement conversion cost.
Step 6
Fully Managed Construction
Our dedicated team of certified basement contractors takes over your basement construction. We manage every trade and inspection, and you can monitor progress 24/7 via your client portal.
Our Reputation
What Our Clients Say
We are proud of the ambitious spaces we create, but the lasting relationships we build with our clients are our greatest achievement. Here is what some of them have to say about their experience with Reltic BIM.
Frequently Asked Questions (FAQ)
FAQs About Basement Conversion
A basement conversion is a significant undertaking. To help you understand the journey from a technical and practical standpoint, here are our answers to some of the more detailed questions we often receive from clients.
Do I always need Planning Permission for a basement conversion?
Any basement conversion project involving excavation (a new dig-out or lowering the floor) or creating/altering lightwells will require Full Planning Permission. We have an excellent track record navigating local council basement policies.
How do you guarantee the basement will be completely dry?
A dry space is non-negotiable for a habitable basement. We use best-in-class basement waterproofing, typically a cavity drain membrane system. All our systems are fully specified and come with a long-term, insurance-backed guarantee.
How is it possible to get natural light into a basement?
Clever basement design is key. We use a range of techniques, from large, walk-on structural glass panels in the ceiling above to multi-level lightwells that can make a new basement space feel incredibly bright and airy.
Does the Party Wall Act apply to basement projects?
Yes, in every case involving excavation or structural work to the foundations of a shared wall. It is a legal requirement for London basement conversions. Our end-to-end service includes managing this complex process for you.
Can I live in my house during a basement excavation?
Yes, it is usually possible, though you should expect significant disruption during the main excavation phase. We create a sealed work zone, often with its own secure access, to completely separate the site from your home. We communicate clearly about the schedule, especially during noisy periods like breaking out the ground floor slab, to minimise the impact on your daily life as much as possible.
How long does a typical basement conversion take from start to finish?
A full basement excavation and fit-out is a major construction project. A realistic timeline should be broken into two phases:
Design & Planning: This typically takes 3-6 months, including all structural engineering, design work, and the statutory wait for a council’s planning decision.
Construction: The on-site build for a standard basement dig-out usually takes between 6-9 months. You should therefore plan for the entire end-to-end process to take approximately 9 to 15 months.
Do I need to hire my own Structural Engineer?
No, you don’t. As part of our fully managed Design & Build service, we coordinate and manage all necessary consultants on your behalf. This includes certified structural engineers, Building Control inspectors, and any other specialists required for your project. This is a core part of our promise to deliver a seamless, hassle-free experience for our clients.
What guarantees and insurance do you provide?
The security of your investment is paramount. During the construction phase, your project is protected by our comprehensive Public Liability Insurance and Contractor’s All-Risk Insurance. Upon completion, we provide our own workmanship guarantee, which is clearly defined in our building contract. This gives you peace of mind both during and long after the project is finished.
Who will be managing my project on a day-to-day basis?
You will have two key points of contact. A dedicated Site Manager will be on-site every day, responsible for managing the construction teams, safety, and quality. Your primary contact will be your Project Manager, who oversees the schedule, budget, and all client communication through your online portal, ensuring you have a single, accountable expert to speak to at all times.
