In 2026, a single-storey rear extension in Kent costs £2,200–£3,400 per m² fitted, including foundations, shell, roof, electrics, plumbing first-fix, plastering and standard floor finishes. Add £400–£800/m² for a kitchen fit-out if it's open-plan. West Kent (Sevenoaks, Tunbridge Wells) sits at the top of that range; east Kent towns like Dover and Folkestone at the bottom. A typical 20 m² rear extension in Maidstone therefore lands between £44,000 and £68,000 before VAT.
Often no — most single-storey rear extensions fall under Permitted Development if they're under 4 m (detached) or 3 m (semi/terrace), don't exceed half the curtilage, and match the host materials. But in the Kent Downs AONB, the High Weald AONB, conservation areas (Canterbury, Faversham, Rye-edge, etc.), and on listed buildings, Permitted Development is restricted or removed. Always apply for a Lawful Development Certificate before building — it's £103 and protects you on resale. For anything ambiguous, a 30-minute pre-application chat with your district council is time well spent.
The CSCS (Construction Skills Certification Scheme) card confirms site-level competence and health-and-safety training. It's not a legal requirement on domestic jobs, but it's near-universal on insured and reputable sites. A builder without a CSCS card for themselves or their team is unlikely to be welcome on a commercial site, which tells you something about their day-to-day standards. Ask to see the card colour: Green (labourer), Blue (skilled worker), Gold (supervisor), Black (manager).
The FMB (Federation of Master Builders) is the UK's largest trade association for builders. Members are vetted (financial, insurance, customer references) and abide by an FMB code of conduct. It's not a regulator — no builder must be an FMB member — but membership is a reasonable quality filter. For larger jobs (£25,000+) the FMB also runs a build-warranty scheme, and FMB-backed contracts are a sensible starting point for anyone doing a big extension or refurb.
For a small job (a few thousand pounds), no deposit is usual. For larger projects, 10–20% on contract signing is reasonable — enough to cover specialist materials ordered in advance, windows, and similar. Anyone asking for 50% upfront, or "half of total now and the rest on completion," is running your cash at risk. Use staged payments tied to milestones (foundations complete, roof on, first-fix, second-fix, practical completion), not time.
Yes, on most domestic alteration and extension work — 20% standard rate. Two important exceptions: new-build dwellings are zero-rated for VAT (the builder reclaims it), and energy-saving measures (insulation, heat pumps, solar) are reduced-rated or zero-rated until at least March 2027 under current policy. Make sure your quote is clear about whether the headline figure includes VAT. "£50,000 plus VAT" is £60,000 — a big difference.
For jobs under £10,000, a simple written quote and agreed schedule is usually enough. For anything above that, yes — a JCT Homeowner Contract (or FMB Home Improvement contract) sets out who does what, staged payments, retention, snagging, warranties, and dispute resolution. It's the single best defence against disputes, and serious Kent builders expect to see one on larger jobs. The JCT Homeowner Contract runs to about 15 pages and is free to download — no solicitor required for a standard residential job.
From site start to practical completion, a typical dormer loft conversion takes 8–12 weeks in Kent. A simple roof-light (Velux) conversion is 4–6 weeks, a hip-to-gable with dormer is 10–14 weeks, and a Mansard (common in Kent's Edwardian terraces) can run 12–16 weeks. Add 3–6 months of design, structural calculations, Building Regulations submission and Party Wall notices before work starts. Allow a full six months from first enquiry to move-in.
Almost always, yes — any opening in a load-bearing wall, any steel beam, any loft conversion, most rear extensions. The Building Control office will require stamped structural calculations before signing off the foundations or the first-floor. Structural engineer fees for a single-storey extension run £600–£1,200 in Kent; for a loft conversion £800–£1,500. A good builder works with one or two engineers regularly and the fee is usually in the quote. If not, it's a separate line to add.
A snagging list is the collection of small defects picked up at or shortly after practical completion — chipped skirting, uneven tile grout, a door that sticks, a radiator valve that drips. Raise them in writing within the first week after handover. Most JCT and FMB contracts include a "defects period" of 6 or 12 months during which the builder must return to fix anything that fails or appears. Don't release the final 5% retention payment until snagging is complete.
Most do — Kent winters are mild by UK standards and a well-prepared builder can pour foundations, close the roof, and work internally through December and January. The bigger weather issues are heavy rain (which delays digging and brickwork) and high winds (which stop crane and scaffold work). Builders often give small discounts on winter starts because their books are quieter between Christmas and March.
At minimum, £2m Public Liability Insurance and £10m Employers' Liability Insurance (the latter is a legal requirement if they have any employees). For larger jobs, a Contractor's All-Risks policy covering works-in-progress, site materials, and temporary structures is standard. For extensions and new builds, also check structural warranty cover — FMB or LABC warranties cover defects for 10 years and are increasingly asked for by mortgage lenders.
If your extension, loft conversion, or basement affects a shared wall or foundation within 3 m or 6 m of a neighbour's structure, the Party Wall etc. Act 1996 applies. You must serve notice on the neighbour at least 2 months before work starts (for wall work) or 1 month (for excavation). Most Kent projects need a Party Wall Agreement ("award") drawn up by a surveyor on each side — fee £800–£1,500 per surveyor, paid by you as the "building owner." Don't skip this; breach of the Act is a civil matter with injunctions available.
Shortlist three for every job above £15,000. Get a quote for the same written scope from each, including VAT and staged payments. Walk one of their finished jobs (most reputable Kent builders will arrange this). Check FMB / TrustMark / CSCS paperwork and insurance. Speak to two previous customers — at least one whose job finished 6+ months ago. Use our Kent builder directory to start a shortlist.
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