London's Bespoke Design & BuildStudio

It means one team handles everything — the architectural design, the planning application, the construction, and the interiors — under a single contract with a single point of contact. The alternative is hiring an architect, then finding a builder yourself, then managing them against each other. That coordination burden falls entirely on you. With design and build, Sovran is responsible for the whole outcome, not just their slice of it. If something needs resolving between design and construction, it is resolved within the same team before it ever becomes your problem.

For a single-storey rear extension in London in 2026, the all-in cost — including VAT, professional fees, and structural work — typically runs between £80,000 and £160,000 at mid-to-high specification. At the luxury tier, with structural glazing, bespoke joinery, and smart home integration, projects start at £200,000 and can exceed £1M depending on scope. Sovran delivers projects from £100k to £25m+. The single biggest variable is not the footprint — it is the specification. Two extensions on identical footprints can differ by £80,000 based purely on material and design choices. The most reliable way to get an accurate number is to develop the design first, then fix the price.

Most single-storey rear extensions in London qualify as Permitted Development — meaning no formal planning application is required. For a terraced house, you can typically extend up to 3 metres from the original rear wall; for a detached property, up to 4 metres. However, London has a higher proportion of conservation areas, Article 4 Directions, and listed buildings than almost anywhere else in the UK — and these remove Permitted Development rights entirely. Sovran’s architectural team includes former planning officers, which is how the company maintains a 95% planning success rate across all London boroughs. We know what gets approved before the application goes in, which saves clients both time and money.

Both — and that is the point. Sovran is a certified design and build company, which means the architectural team, the planning specialists, and the construction team all sit under one roof. Founded in 2011, the company has delivered over 1,000 projects across London ranging from home extensions and loft conversions to full house renovations, basement conversions, commercial fit-outs, and hospitality projects.

There are two timelines to separate: the pre-construction phase and the build itself. Pre-construction — design, planning, structural engineering, party wall — typically takes 3 to 6 months depending on whether planning permission is required. The build phase varies by project type: a single-storey rear extension takes 10 to 16 weeks on site; a loft conversion 6 to 14 weeks; a double-storey extension 16 to 22 weeks. Sovran works to a fixed programme agreed at the start of each project, with milestone reporting so you always know where things stand.

Sovran works across the whole UK — the boroughs where the company is most active include Kensington, Chelsea, Notting Hill, Hampstead, Fulham, Wimbledon, Wandsworth, Islington, and Richmond, as well as the wider Surrey commuter belt. The company has a London showroom and delivers projects both locally and internationally — the portfolio includes a hotel project in Bali alongside residential work across the UK. If you are based outside these areas and want to discuss a project, it is worth a conversation; the best starting point is a discovery call.

Sovran works to fixed-price contracts, agreed after the design is fully developed. The price is not set from a rough estimate — it is set from a complete scope of works, structural survey, and detailed drawings, so there is a real foundation for the number. That said, Victorian and Edwardian London properties do occasionally produce structural surprises when walls open up. Sovran recommends holding a 10 to 15% contingency for this reason. Any variations beyond the agreed scope are discussed and approved before work proceeds; there are no surprises added to the final invoice.

The Party Wall Act 1996 requires you to formally notify adjoining neighbours before any structural work close to a shared boundary — which applies to almost every London terrace or semi-detached extension and loft conversion. If a neighbour appoints their own surveyor, you pay both sets of fees: budget £700 to £1,400 per neighbour, potentially £2,800 on a mid-terrace with two neighbours. The process adds 4 to 8 weeks to the pre-start programme if neighbours take time to respond. Sovran serves party wall notices early and manages the process as part of the project. In many cases, Sovran’s structural team can design around notifiable work where possible, reducing both the cost and the timeline impact.

The numbers usually favour extending — but it depends on your specific situation. The transaction costs of moving home in London — stamp duty, estate agent fees, legal costs, and the premium for a larger property — typically total £50,000 to £100,000 or more, and that money is spent, not invested. A well-designed home extension adds equivalent living space and typically increases property value by 10 to 20%; a loft conversion by 15 to 25%. Both keep the investment on your balance sheet. Moving makes more sense if you need to change area, if your current plot cannot accommodate the space you need, or if planning constraints make a worthwhile extension impossible. A discovery call with Sovran will usually give you a clear picture of what is feasible within 30 minutes.

The first step is to book a discovery call, which you can do directly from our Contact page. In that call, the team listens to what you are trying to achieve, gives an honest initial view of feasibility and likely cost range, and explains what the process looks like for your specific project type. There is no obligation and no pressure — if Sovran is not the right fit for your project, they will say so. You can also reach our team by phone on +44 7516 100111, by email at info@sovrangroup.co.uk, or via WhatsApp.