From £35,000 rear extension to £150,000 wrap-around build — add square footage and 15-20% to your London property value. Free site visits, written quote.
A house extension is one of the most transformative changes you can make to a London home — adding genuine square footage, opening up your living space, and significantly increasing property value. TrustBuilt Projects handles everything: structural design, planning applications, foundations, build, services and finishing.
We've built extensions across every kind of London property — from compact side-returns in Battersea flats to substantial wrap-arounds on Hampstead semis. Every project is quoted in writing after a free site visit.
We visit your property, measure up, listen to your vision, and ask the right questions about what you need.
Written quote after the free site visit.
All work managed end to end by us. Daily progress updates if you want them, clean working practices throughout.
Final walkthrough, snagging, full clean. We leave your property spotless and stand behind every detail.
These are typical London market ranges for 2026 — a realistic guide for budgeting, not a fixed price list. Your exact figure depends on size, spec and structural work, so we give you a fixed written quote after a free site visit.
Mid-spec London builds run roughly £2,800–£4,500 per m², including structural work, glazing, electrics, plumbing, plastering and decoration. Architect/planning fees, kitchens and premium finishes are usually separate.
A small rear extension costs far less than a double-storey or wrap-around — floor area is the single biggest driver.
Steel beams, deep foundations, underpinning and removing load-bearing walls all add to the build.
Bi-fold doors, roof lanterns, skylights and flat-vs-pitched roofs change both cost and lead time.
Many extensions house a new kitchen or bathroom — the fit-out is often quoted separately.
Conservation areas, full planning applications and party-wall agreements add fees and time versus permitted development.
Flooring, joinery, underfloor heating and the level of finish move the final figure up or down.
Want an exact figure for your home? Book a free site visit → and we’ll send a fixed written quote.
A typical house extension in London ranges from £35,000 for a small side-return to £150,000+ for a large double-storey build. Most rear extensions land between £40,000 and £70,000. We provide a written quote after the free site visit.
It depends on the size, location and property type. Many single-storey rear extensions fall under permitted development (up to 6m on terraces and semis, 8m on detached, subject to neighbour consultation). Double-storey, side, and conservation area extensions usually need full planning. We'll advise during the free site visit.
Most extensions take 10 to 20 weeks. A simple side-return can be done in 10–14 weeks. Larger wrap-arounds and double-storeys take 16–24 weeks. Weather, planning delays and bespoke materials can add time — we'll be honest about timelines.
Yes, most extensions are built around your daily life — the existing house stays sealed and habitable, with the build happening externally until 'break-through' (where we knock through the existing wall to connect the extension). We agree the break-through timing with you so you can plan around it.
All extensions require Building Regulations approval, which we handle as part of the project. This covers structural integrity, fire safety, energy efficiency, and ventilation. Sign-off is included in our quote.
If your extension affects a shared wall with a neighbour (very common in London terraces and semis), yes. We can guide you through the Party Wall Act process and recommend trusted surveyors if needed.
Yes — bricks, mortar, windows, roof line, all chosen to either match seamlessly or contrast intentionally (modern glass box vs. traditional brick, for example). You decide the look. We can show you previous projects for inspiration.
Combine with a kitchen extension to create the open-plan family space everyone wants.
Learn more →Pair with a loft conversion for maximum space and property value.
Learn more →We handle all structural work including steels, foundations, and load calculations.
Learn more →Local extension pages for the areas we work in most: