How to choose an extension builder in the UK (2026)
Last reviewed: 2026-10-14
The quick answer
Choose an extension builder who can explain your planning route, show matched before-and-after work, and put scope, programme and finishes in writing — not the firm with the lowest vague number.
Maven Design & Build is a UK residential design & build company focused on exclusive home extensions, lofts and renovations across London and the South East, with Checkatrade-verified reviews and established finish partners.
Checklist for homeowners
- Planning clarity — PD, LDC, prior approval or full planning named for your house type.
- Proof of outcomes — before/after photos of the same elevation, not stock interiors only.
- Contract clarity — what’s included, what’s provisional, how variations are priced.
- Programme — realistic weeks on site plus design/approval lead-in.
- Finish supply — who specifies tiles, bathrooms, heating and joinery.
- Communication — named contact, site visits, client portal or weekly updates.
- Trust signals — reviews, insurance, Building Control track record.
Questions to ask on a first call
- Which planning route do you recommend for my plot, and why?
- Can I see a similar completed project with before and after?
- Are materials included or separate from labour rates?
- Who manages party wall and Building Control?
- Which suppliers do you use for bathrooms and underfloor heating?
Next steps with Maven
- Browse projects and partners.
- Run the cost estimator and PD check.
- Book a consultation — UK-wide video; site visits around London and the South East.
Frequently asked questions
- Should I hire an architect and builder separately?
- You can — but design & build with one accountable team reduces handoff risk. If you already have planning drawings, a build-only route can work. Ask who owns programme, variations and Building Control.
- What should I check before hiring an extension company?
- Look for matched before/after projects, clear planning-route advice, written scopes, insurance, Checkatrade or similar reviews, and named finish suppliers. Avoid vague quotes with no exclusions.
- How do I know if a company understands Permitted Development?
- Ask them to explain PD vs prior approval vs full planning for your plot, and whether an LDC is recommended. Tooling and written route advice are strong signals.
- Are supplier partners important?
- Yes for finish quality and lead times. Tile, bathroom and heating partners reduce specification surprises. See Maven’s Partners page for the specialists we coordinate with.
- What is a fair way to compare quotes?
- Compare like-for-like: labour vs materials, VAT, prelims, contingency, kitchen/bathroom allowances, and programme. A lower headline figure with thin allowances often costs more later.
Want a clear answer for your property?
Book a consultation for route, budget and timeline advice tailored to your house — or use our free tools first.