Looking Below: Designing Better Basements In London

In London’s dense and conservation-conscious neighbourhoods, where rooflines are protected and rear gardens closely regulated, basement extensions have become an increasingly common way for homeowners to gain much-needed space. Whether it’s to accommodate a growing family, create a home office, or simply bring some breathing room into daily life, the decision to build downwards can offer both practical and architectural opportunities—if done well.

At Unagru Architecture Urbanism, we’ve delivered basement projects across Kensington, Hackney, Brent, Camden and Chelsea. For us, a basement is never just a space-making exercise—it’s a chance to rethink the home. We design them to be filled with light and possibility, shaped by the same clarity and care as the rest of the house. And crucially, we approach each project with the understanding that the best design delivers maximum benefit with minimum environmental and structural intervention.

Why Consider A Basement Extension?

In areas where land is expensive and planning regulations are tight, basements often offer the most viable option for adding space without compromising the urban fabric. In prime boroughs like Kensington and Chelsea, property values often exceed £15,000 per square metre. Extending below ground can provide much-needed flexibility for families without the upheaval of moving.

But while basements are increasingly common, they’re far from routine. Every site presents its own challenges—technical, regulatory, even social. The best solutions begin with a deep understanding of place, structure, and lifestyle. At Unagru, we believe in designing not just to add space, but to improve how people live within it.

From Storage To Sanctuary: The Modern Basement

The role of the basement has evolved dramatically. No longer just for storage or plant rooms, they now often serve as central living spaces. The shift has been particularly noticeable since the pandemic, which highlighted the importance of adaptable environments within the home.

At The Sponge in Queen’s Park, we designed a basement that is actively involved in the life of the house. A slatted timber wall encloses the staircase, offering both a sculptural presence and a spatial filter between the upper living and dining spaces. The basement itself is flexible: a study and media room can be closed off with curtains or sliding doors, while other areas remain open and adaptable.

In Kensington, at Cambridge Place, the basement became the new social centre of the home. By carefully lowering the rear garden, we were able to introduce a dining room that connects fluidly with the kitchen and opens directly onto a new paved terrace. What might have been a dark and enclosed level became an airy, outward-looking part of everyday life.

The Garden Connection: Bringing Basements To Life

A key consideration when designing a basement is its relationship with the garden. Far from being a self-contained space, a well-designed basement should have a visual and physical dialogue with the outside. Lightwells—whether open or covered—play a crucial role, not only by introducing daylight but by allowing for continuity between levels, materials, and moments of use.

At The Sponge, the basement is accessible both internally and externally via a staircase clad in dark, stacked bricks that match the garden paving. This dual access transforms what could be a private retreat into a part of the home’s wider circulation system. The result is a circular flow—garden to basement to house and back again—that energises the entire space and avoids the sense of spatial dead-ends often found in garden extensions.

Similarly, at Studdridge Street, a small lightwell and a set of bright white steps provide light, views, and an architectural anchor within the garden’s landscaping. These modest interventions make a meaningful difference: the garden is no longer a separate zone but part of a wider domestic sequence. Social gatherings can evolve naturally—from drinks in the garden to films in the media room, or table tennis tournaments that last into the evening.

By aligning garden design with basement architecture, we create spaces that are both integrated and alive—tuned to the rhythms of daily life and rich with possibility.

Light From Above: Tradition And Influence

The act of bringing light into a basement—drawing daylight from above into the heart of a building—is both a technical challenge and a long architectural tradition. One of the most poetic lessons I received in this came from Elias Torres Tur, my teacher at ETSAB in Barcelona, whose work often explored the beauty of “luz cenital”—zenithal light that falls directly from above. It’s a concept that creates drama without spectacle: shafts of natural light that focus, frame and animate space.

The same sensibility is found in the work of John Soane, perhaps the most inventive manipulator of daylight in British architecture. His masterpiece, the Dulwich Picture Gallery, is lit almost entirely from above—its rooflights casting an even, contemplative glow on the paintings below. But nowhere is his legacy more resonant than in the John Soane Museum. There, light travels miraculously through rooms and staircases, mirrored surfaces and voids. It’s a labyrinth of thresholds and reflections, a true masterclass in how to make underground spaces breathe. In many ways, it remains the finest example of a London basement extension—elegant, efficient, and entirely experiential.

This legacy continues to inspire our own work. At The Sponge, the central stair is more than a connector—it’s a lightwell, a spatial fulcrum, and an atmospheric device. Its slatted enclosure doesn’t just shape circulation; it filters daylight from above, softens shadows and adds texture to everyday movement.

Enclosed Light, Cultivated Calm

The use of lightwells and enclosed patios to bring nature and daylight into otherwise introverted spaces has deep roots in architectural history. Japanese courtyard houses, such as those explored by Tadao Ando, offer carefully controlled interactions between interior and exterior. His excavated courtyards are not just light sources—they are spatial voids carved to invite stillness, balance and reflection.

This architectural impulse appears again and again across cultures. In India, the work of Studio Mumbai revives courtyard traditions as both climatic and social tools. Across the Mediterranean, from Morocco to Naples, patios were designed to collect water, tame the wind, and give homes a breath of sky. Ancient Pompeian houses—dense, urban and inward-looking—used their atria and peristyles not only as status symbols, but as climatic regulators and sources of gentle light.

These traditions resonate deeply in our work. We design lightwells and garden-level courtyards not as technical appendages, but as quiet protagonists. They’re places where children play, where plants thrive, and where a shaft of morning light can become an architectural event. In a way, these are the new domestic piazzas—open-air rooms folded into the life of the house, carefully shaped to bring a moment of landscape into the everyday.

Why Basement Projects Require Experienced Professionals

Basement projects are not for beginners. They require coordination between architects, engineers, surveyors, planners and builders—all working with precision and foresight. In our experience, successful basements are the result of collaboration, craft, and calm problem-solving.

1. Structural Engineering

Working below ground in London means dealing with party walls, shallow foundations, and occasionally fragile neighbours. At Cambridge Place, a Georgian terrace in the De Vere Conservation Area, we faced all three. Years of ad hoc modifications had left the structure unbalanced. Our design reinstated clarity, stabilised the building, and introduced a fully connected lower ground level—all while working within heritage constraints.

At The Sponge, neighbour concerns were addressed early through a coordinated meeting between our team, the structural engineer, and both sides’ party wall surveyors. Clear information, transparency, and mutual respect allowed us to proceed with confidence.

2. Waterproofing

London’s clay soil, heavy rainfall and high water tables make waterproofing essential. We typically specify Type C systems—waterproof concrete combined with internal membranes and perimeter drainage linked to sump pumps.

Installation is everything. We require all contractors to attend certified training, and we often work with waterproofing consultants to ensure every detail is right. The goal is to design a system that quietly and reliably disappears into the background—keeping the basement dry, year after year.

3. Planning and Impact Assessments

In boroughs such as RBKC and Camden, basement proposals are scrutinised carefully—and rightly so. Basement Impact Assessments (BIAs) must cover everything from structural integrity and drainage to construction noise, waste removal and cumulative neighbourhood impacts.

Our recent project in Hackney, beneath a locally listed detached house, required a particularly thorough planning strategy. The house’s large footprint and deep garden allowed us to create a generous basement, but its heritage status demanded sensitivity. We incorporated lightwells within planted courtyards and concealed plant to preserve the garden’s character. The result feels both substantial and discreet.

4. Ventilation and Air Quality

Good basements feel natural, not subterranean. That depends as much on air as light. Mechanical Ventilation with Heat Recovery (MVHR) systems provide consistent, filtered air throughout the year—essential for wellbeing and energy efficiency.

In our Chelsea project at Studdridge Street, the basement includes a play area, studio, and guest accommodation. MVHR ensures these spaces are comfortable and fresh, without the need for open windows or compromise on insulation.

Financial Considerations 

Basement extensions in London typically cost between £5,000 and £8,000 per square metre, with professional fees, VAT and contingency adding 30–40% to overall budgets. It’s a serious investment. But in many cases, the value returned—in terms of space, flexibility, and quality of life—justifies the cost.

At Cambridge Place, the new basement unlocked the rear of the house, connected inside and outside, and restored a coherent plan. At The Sponge, the basement added a calm, adaptable space to a compact family home—improving not just the square footage, but how the house is lived in.

Final Thoughts

Basements are not simply about making more space. They’re about making better space—places where families can grow, rest, work, and live well.

At Unagru, we approach basement design with the same care we bring to every project: clarity of structure, simplicity of form, and a strong connection to light and life. We don’t build big for the sake of it. We build what’s needed, and we build it well.

If you’re considering a basement, let’s talk about what it could be—not just underneath, but at the heart of your home. Click here to contact us.