{"id":5480,"date":"2026-06-15T14:40:38","date_gmt":"2026-06-15T14:40:38","guid":{"rendered":"https:\/\/www.buildteam.com\/blog\/?p=5480"},"modified":"2026-06-15T14:53:51","modified_gmt":"2026-06-15T14:53:51","slug":"how-can-i-get-a-realistic-builders-quote","status":"publish","type":"post","link":"https:\/\/www.buildteam.com\/blog\/how-can-i-get-a-realistic-builders-quote\/","title":{"rendered":"How to Get a Realistic Builder’s Quote"},"content":{"rendered":"

A realistic builder’s quote is fixed (not an estimate), itemised, and states clearly what is included. For a single-storey London extension in 2026, expect construction of about \u00a32,800 to \u00a35,000+ per m\u00b2<\/strong>, with professional fees adding 10 to 15%, a 10 to 20% contingency, and 20% VAT on top. Pay a deposit of no more than 10 to 20%, then stage payments tied to milestones, never the full amount upfront. Be wary of any quote that comes in well below the others.<\/p>\n

With the cost of moving in London now averaging around \u00a332,786, many homeowners are choosing to improve rather than move. Builders have felt it: the Federation of Master Builders reported enquiries swinging to +34% in 2025. But an extension only pays off if it is priced properly from the start. The difference between a realistic quote and an optimistic one is the difference between a project that lands on budget and one that overruns. Here is how to get a quote you can trust, what a realistic one should cost, and how to pay it safely.<\/p>\n

What should a realistic extension quote cost in 2026?<\/h2>\n

As a London benchmark for a single-storey extension in 2026:<\/p>\n\n\n\n\n\n\n\n
Extension size<\/th>\nConstruction (\u00a3\/m\u00b2)<\/th>\nAll-in (incl. fees, contingency, 20% VAT)<\/th>\n<\/tr>\n<\/thead>\n
Small single-storey (15 to 20 m\u00b2)<\/td>\n\u00a32,800 to \u00a34,500<\/td>\n\u00a365,000 to \u00a395,000<\/td>\n<\/tr>\n
Medium single-storey (20 to 30 m\u00b2)<\/td>\n\u00a32,800 to \u00a35,000+<\/td>\n\u00a390,000 to \u00a3150,000<\/td>\n<\/tr>\n
Side return (typical 12 to 15 m\u00b2)<\/td>\n\u00a34,500 to \u00a35,500<\/td>\n\u00a355,000 to \u00a385,000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

These are indicative figures and exclude kitchen units, furniture and landscaping unless stated. Side returns cost more per m\u00b2 than larger rear extensions because of their complexity. For the full picture, see our guide to how much an extension costs in London<\/a>. London rates run 20 to 40% above the national average, and building costs are forecast to keep rising, so a fixed price with a stated validity period matters.<\/p>\n

Ten steps to a realistic builder’s quote<\/h2>\n

A realistic quote does not happen by chance. It comes from defining the work clearly, asking the right questions, and knowing what a trustworthy quote contains. These ten steps take you through the process from first drawings to signed contract.<\/p>\n

1. Start with detailed plans<\/h3>\n

A builder can only price accurately what is clearly drawn. Invest in measured drawings from an architect or designer: floor plans, elevations and a written specification. The more precisely the work is defined, the fewer assumptions the builder has to make, and assumptions are what turn into extra costs once the job is underway. Vague plans produce vague quotes that move the moment work starts.<\/p>\n

2. Define exactly what is included<\/h3>\n

Be specific about scope. Spell out who digs the foundations, who handles the plastering, plumbing and electrics, and whether the builder is delivering a finished room or just the shell. For a conversion, say whether insulation, structural steel and a staircase are part of the price. Arrange a site visit so the builder can assess access, drainage and ground conditions in person, because a quote written from drawings alone misses what a walk around the site reveals.<\/p>\n

\"Rear\n
Defining the work clearly, from foundations and slab through to the structure, is what lets a builder price accurately.<\/figcaption>\n<\/figure>\n

3. Get three comparable quotes<\/h3>\n

Prices vary widely, so get three, from builders chosen on personal recommendation and consistent reviews. Give each the same information and ask for a fixed quote on the same scope, so you are comparing like with like rather than guessing at the differences. Resist the urge to take the lowest on sight: a quote well below the others usually signals corners that will be cut or costs that will reappear later as extras.<\/p>\n

4. State your budget honestly<\/h3>\n

Sharing your budget does not inflate the quote, despite the common worry that it will. It lets a good builder tell you what is realistically achievable for the money, and where sensible compromises lie, rather than designing something you cannot afford and stripping it back later. An honest budget conversation at the start saves an expensive redesign down the line.<\/p>\n

5. Ask for a full cost breakdown, with VAT shown<\/h3>\n

A trustworthy quote itemises labour, materials, subcontracted work such as plumbers and electricians, and specialist items like steel, glazing and insulation, rather than presenting a single lump sum. Confirm the builder is VAT registered and whether VAT is included. Most extension work carries the standard 20% VAT, though a reduced 5% rate can apply to a home empty for two or more years and to certain conversions (HMRC VAT Notice 708). On a \u00a350,000 job the difference between 20% and 5% is \u00a37,500, so it has to be clear which applies.<\/p>\n

\"Red\n
Structural steel is a specialist line item. Here the steel frame is set out before the extension is built up.<\/figcaption>\n<\/figure>\n

6. Know what is not included<\/h3>\n

What a quote leaves out matters as much as what it covers. Get the exclusions in writing so you can budget for them separately and avoid surprises. The items most commonly excluded are planning and building control fees, architect’s fees, kitchen and bathroom fittings, landscaping, and temporary site access or waste removal. A quote that looks cheaper than the rest is often simply a quote that excludes more.<\/p>\n

7. Agree a realistic timeline<\/h3>\n

Time is money on a building project, and an unrealistic programme costs more, because a builder forced to rush or bring in extra labour will price that in. Be honest about when you hope to start and finish, and allow some flexibility for weather and material lead times, which can hold up even a well-run job. A credible quote comes with a credible programme attached, not just a price.<\/p>\n

8. Check the provisional sums and PC items<\/h3>\n

Many quotes contain allowances for things not yet decided, and these are where final bills drift. A provisional sum is an estimate for work not fully defined yet, such as groundworks or drainage, which is settled at its actual cost as the work is done. A Prime Cost (PC) item is an allowance for a product you have not chosen, like tiles or kitchen units; if you pick something dearer, a variation covers the difference. Most contracts called “fixed price” can still move on these allowances, so check they are realistic and not set artificially low to keep the headline figure down.<\/p>\n

\"Rear\n
Structural work like this is often covered by a provisional sum until the ground and existing structure are fully exposed.<\/figcaption>\n<\/figure>\n

9. Research the builder and check accreditation<\/h3>\n

A good quote means nothing from an unreliable firm. Ask for references and recent projects of the same type, speak to those clients if you can, and confirm the builder holds public liability insurance. Check membership of a recognised body: the Federation of Master Builders (FMB) independently vets its members and inspects their work, TrustMark is the only Government-endorsed scheme and carries insurance-backed guarantees, and the NFB and CIOB are further marks of vetting and professional standards. Verify membership on the day you sign, because registrations lapse annually and online listings go stale.<\/p>\n

10. Insist on a fixed-price quote, not an estimate<\/h3>\n

A fixed-price quote is a committed figure that becomes the contract and only changes if you change the work. An estimate is a rough figure that can drift during the build, so it offers far less protection. Get everything in writing: the fixed price, the payment stages tied to milestones, the start and finish dates, and the terms. This is the document that protects both you and the builder if anything is disputed later.<\/p>\n

How much deposit should I pay a builder, and how?<\/h2>\n

Never pay the full amount upfront. A deposit of 10 to 20% is reasonable on a larger job to cover initial materials, occasionally up to 25% where the builder has to buy specialist materials or hire equipment early. Anything much higher, especially before work starts, is a warning sign. After the deposit, pay in stages tied to completed milestones, for example foundations complete, structure watertight, and final completion. Each stage should be set out in the contract.<\/p>\n

Two safeguards are worth holding to: do not pay in cash, because a cash payment is untraceable if a dispute arises and offers no consumer protection, and do not release the final payment until Building Control has issued its completion certificate. Staged payments keep the builder accountable to the programme and protect your money if anything goes wrong.<\/p>\n

\"Warm\n
The structure reaching watertight stage, a natural point for a staged payment.<\/figcaption>\n<\/figure>\n

Can a builder increase a fixed-price quote?<\/h2>\n

Only in defined circumstances, and only with your written agreement. A fixed-price contract holds for the work specified in it. The price can legitimately change through a variation, which is a change you request, or through the provisional sums and PC items above settling at their actual cost. What a builder cannot do is raise the price unilaterally for work already in the contract. If a builder asks for higher deposits, unexpected stage payments, or a larger final balance without a written variation, treat it as a red flag and pause. Agree any change in writing before the work is done.<\/p>\n

What questions should you ask a builder before hiring?<\/h2>\n

The right questions separate a reliable builder from a risky one. Before you sign, ask:<\/p>\n