Basement Conversion

Among the top residential architecture firms in London, Scenario Architecture has built a solid reputation expanding and enhancing homes across the city. Our architects distil the ambitions of today’s homeowners into hard-working houses that express the past and look to the future. We specialise in striking interiors that maximise space and welcome natural light. The Scenario client aspires to a new archetype for London living: open, comfortable and luxurious yet accessible.

We founded Scenario with an ambitious mandate: to adapt our signature style to the needs of a growing family. We collaborate every step of the way with our clients to create highly functional interiors that make the best use of their investment. Scenario’s bespoke architecture tells the story of the homeowner, not the architects.

Our portfolio of new and heritage properties includes Scenario House, an East London terrace house we expanded in nearly every direction to accommodate the busy and evolving lifestyle of its owners. In 2018, Scenario House was shortlisted for several prestigious prizes, including the RIBA London Awards.

Basement Conversion

Full refurbishment to a terraced house within a conservation area

Basement Conversion

Contemporary rear extension to a Victorian house

Basement Conversion Your intention to convert a basement

Starting your basement conversion

We’ve drawn up this illustrated overview to help you understand each stage of your home renovation and extension. And we’ve created a step-by-step guide to help see you through the planning permission process. It deals with the ins and outs of UK planning and offers strategies for navigating the system, based on our own successes.

Most home extensions and basement conversions require planning permission from the council in question. Scenario has been successful in securing this permission on behalf of our clients.


Discover if your architect has had success steering planning applications through your local council. Visit the “planning applications” page of your council’s website and enter the architect’s name in the search criteria.

Basement Conversion


To help you understand what it takes to obtain planning permission to convert a basement in London, we’ve created this helpful guide. Download it below.
Planning guide

Basement Conversion Basement Conversion with Scenario Architecture

Working with Scenario Architecture on your basement conversion

Our boutique architecture practice specialises in home expansions of every scale and complexity. We offer a truly bespoke service, collaborating with homeowners on every stage of the process, from the initial designs to the project’s completion.
All our architects are fluent with the latest 3D design and visualisation tools. They use real-time visualisations and virtual reality to choose finishes and fixtures, maximise living space and simulate natural light. Our construction information comes from accurate 3D building information modelling (BIM) technology that saves the client time and money. This case study from the Chartered Institute of Building (CIOB) demonstrates the benefits of advanced technology for domestic architecture.
Scenario is a RIBA Chartered Practice, complying with the strict health and safety measures of the Royal Institute of Chartered Architects.

Basement Conversion

Chelsea basement extension below garden level for a home gym. Chelsea, London

Basement Conversion

Extensive renovation within a conservation area of a terraced house. Camden, London

Basement Conversion

Semi basement extension and full refurbishment of a family home. Hackney, London

Basement Conversion >> Your Basement Conversion Project Further Reading

Basement conversions have got a bad rap over the years, from households digging down multiple levels and edging dangerously close to their neighbours’ property lines. These “mega-basements”, or so-called iceberg houses, cause controversy for their deluxe features, like swimming pools, cinemas, wine cellars Turkish baths and car parks.

Building below street level can significantly increase the size of a home where conservation laws restrict expanding up and out. And new rooms below the main floor almost always make financial sense in high-value areas like London. But the more commonly sought and approved versions seek to enlarge an already existing coal hole or cellar. Even the most basic below-ground extensions will cost the same as a loft conversion, yet they’ll provide far more space for the outlay – most basement conversions in London start at about 40 square metres in size, growing to nearly 200 square metres.

Most basement conversions will require local Building Regulations approval, a sign-off from the neighbours and savvy planning. As most existing subterranean spaces lack any significant head height, most require excavation and underpinning. The height of the water table and location of sewer drains are an issue. And if the space lacks any access to light, a lightwell, an opening in the home’s entryway or glazing in the interior stairwell will need to be considered. If your basement conversion forms part of a larger all-over renovation, you can fold the assessment and application costs into your overall budget.

All that aside, converting a basement makes sense for families that intend to stay put and use it. Anyone looking for extra storage space, a separate playroom for growing children or a tucked-away space for utilities will find all these can be covered off in a single excavation. A well-planned basement can be the difference between staying in a beloved city home or leaving for the outskirts.

To make the most of your investment, you’ll want to consult an architect well versed in the local building codes and permissions protocol, and experienced in converting the vernacular architecture. If your home dates back more than a century, an architect that deals in period properties will be able to assess ballpark costs and potential risks with a single meeting. A good architect will be on hand throughout your project, overseeing quality control and serving as a liaison until the basement is properly executed.

Talk to us about your project

We would love to hear about your project and discuss how we can help

Please use the link below to schedule a call at a convenient time

Select a day


Select a time


Contact Information

Any information you provide us remains strictly confidential


Any information you provide us remains strictly confidential

Ownership status for the project

The property is

Any information you provide us remains strictly confidential

Property type

The project is

Any information you provide us remains strictly confidential

Aims of the project

Your budget

Any information you provide us remains strictly confidential

Please indicate an estimate of your target budget (excluding VAT and professional fees) so we can advise on the viability of your requirements

Budget range

Additional information

Any information you provide us remains strictly confidential

Please attach files such as plans, estate agent brochures, image and surveys

Basement Conversion In our clients words


We wanted to renovate our house in a conservation area in central London. Given this involved a complete demolition and new build with an extra floor on top, getting planning approval was always going to be tricky. Scenario did an amazing job on the new house ‘envelope’ and throughout the planning phase. We couldn’t have wished for better from them and having succeeded in gaining planning approval owe them a very big ‘thank you’.


Scenario designed a kitchen extension for us, and we are delighted with the results. The process was well organised, planned and delivered, and the whole team were a pleasure to work with. I would highly recommend them for their design, planning and project management skills.


Worked with these guys on the internal development of our office. From start to finish they were great. They got what we wanted first time and really made working with them very easy. Their aftercare has been great too helping us deal with something that they were not involved with in the first place. Will highly recommend them to anyone.

See all Google reviews