Extension Quote Template Example for UK Builders

A Complete Extension Quote Template Example

Below is a realistic worked example for a single-storey rear extension in the East Midlands. The customer is a homeowner (a consumer, not a business), the builder is a sole trader registered for VAT, and the project runs across eight weeks. Read it in full first, then the sections that follow explain each part in detail.

Quote reference: TDB-2025-047. Date issued: 14 July 2025. Valid for: 30 days (expires 13 August 2025). Prepared by: Dan Bridgman Building, 12 Hawthorn Lane, Nottingham, NG7 4PQ. UTR: 1234567890. VAT registration: 123456789. Prepared for: Mr and Mrs C. Fowler, 34 Elm Drive, Nottingham, NG5 2RR.

Scope of works: Supply of all labour and materials to construct a single-storey rear extension measuring 4m x 5m (20 sq m), comprising: strip foundations to engineer's specification (engineer fee excluded and quoted separately by Steadfast Structural, ref SS-2025-112); blockwork cavity walls; beam-and-block floor; flat roof with EPDM covering and two roof lights (specified: Fakro FTT U8, 78x98cm); bi-fold door opening (supply and fit: three-panel aluminium bi-fold, colour anthracite grey RAL 7016); internal plastering, skim finish throughout; first-fix carpentry only (second-fix excluded from this quote); connect to existing drainage (CCTV survey to be commissioned by client before works commence; any remedial drainage works will be priced as a variation). All works carried out in accordance with Building Regulations Approved Documents A, C, F, L, and M where applicable.

Price summary (all figures inclusive of VAT at 20%): Groundworks and foundations: £4,200. Blockwork, lintels, and DPC: £6,800. Structural steel (supply and install, fabricator quote attached): £2,400. Beam-and-block floor and screed: £3,100. Roof structure, EPDM, and roof lights: £7,500. Bi-fold door supply and fit: £4,600. External render (sand and cement, two coats): £2,200. Internal plastering: £3,800. First-fix carpentry and internal stud partition: £1,900. Skip hire (two skips, estimated): £680. Scaffolding (erect, hire eight weeks, strike): £1,850. Sundries and fixings allowance: £420. Net total: £39,450. VAT at 20%: £7,890. Total contract price: £47,340.

• •Stage 1 payment (mobilisation, due before works commence): £9,468 (20%)
• •Stage 2 payment (foundations complete and inspected): £9,468 (20%)
• •Stage 3 payment (wall plate level): £9,468 (20%)
• •Stage 4 payment (roof watertight, bi-folds fitted): £9,468 (20%)
• •Stage 5 payment (practical completion, snagging signed off): £9,468 (20%)

Payment Terms, Retention, and What the Law Says

The payment schedule above is not just good practice; it is underpinned by the Housing Grants, Construction and Regeneration Act 1996 (the Construction Act), as amended by the Local Democracy, Economic Development and Construction Act 2009. Under the Construction Act, any construction contract for works over 45 days (or where the parties agree) must include an adequate payment mechanism with a payment notice and a pay-less notice procedure. For sole traders working under a written contract with a consumer, stage payments are the standard mechanism that satisfies this.

In practice, this means your quote must state: the amount of each stage payment, when each payment becomes due, and the final date for payment after the due date. A common approach is to state that payment is due on the date the stage is reached, with a final payment date of 14 days later. If the customer does not pay by the final date, the Construction Act gives you the right to suspend works after giving seven days notice in writing, without being in breach of contract yourself. That is a powerful clause worth including explicitly in your terms.

The Scheme for Construction Contracts (England and Wales) Regulations 1998 acts as a default where a contract does not include an adequate payment mechanism. It fills in the gaps, but the Scheme's default payment intervals and notice periods may not suit how you work. Far better to write your own clear payment terms into the quote and have the customer sign them, than to rely on the Scheme to sort it out after a dispute starts.

One practical note on retention: many builders building for a consumer will not include a formal retention, but if you do, state the percentage, the sum it applies to, and the release event clearly. A vague retention clause is the single most common cause of final-payment disputes on extension jobs.

• •State the due date and final payment date for every stage
• •Include a seven-day suspension notice right referencing the Construction Act
• •Avoid vague language like 'payment on completion' without defining completion
• •If charging a mobilisation payment, make clear it is non-refundable after materials are ordered

The Scope of Works Section: Why Vagueness Costs You Money

The scope of works is the section that will be read out in a small claims court if the job goes wrong. Every item that is excluded must be named. In the example above, second-fix carpentry, the structural engineer's fee, and remedial drainage works are all explicitly excluded. That is not pedantry; it is the difference between a £500 dispute and a £5,000 dispute.

Under the Consumer Rights Act 2015, section 49, services must be performed with reasonable care and skill. Section 51 says the price must be reasonable where it is not agreed in advance. These two sections together mean that if your scope is ambiguous, a court may decide the customer's interpretation of what was included is the correct one, and that you should have charged more for it if you wanted to. Clear exclusions are your defence against that outcome.

A well-written scope also handles provisional sums correctly. In the example, the structural steel is listed with a note that the fabricator's quote is attached. That is a fixed-price allowance. The drainage CCTV survey is a genuine provisional sum, meaning the final cost is unknown at quote stage. Mixing these two categories up, or not labelling them, is how builders end up absorbing costs they never priced.

Always list the standards and Approved Documents your works will comply with. For an extension, that typically means Approved Documents A (structure), C (site preparation), F (ventilation), L (energy efficiency), and M (access). Stating this in the quote demonstrates competence and gives the customer confidence, but it also sets the standard against which your work will be judged. Do not list an Approved Document you do not intend to comply with.

• •List every exclusion explicitly: groundworks below a certain depth, external landscaping, decorating, second-fix items
• •Distinguish between fixed-price allowances and genuine provisional sums
• •Name the specific products or specifications where the customer has a choice (bi-fold colour, roof light model)
• •Reference the relevant Approved Documents by letter

Cancellation Rights for Consumer Contracts

If you visit the customer's home to discuss the job and then send them a quote, or if the contract is signed anywhere other than your permanent business premises, the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013 apply. The customer has a statutory 14-day cancellation right. This is not optional and you cannot contract out of it.

What this means for your quote is straightforward: you must include a cancellation notice. The Regulations require you to inform the customer of this right before the contract is concluded. If you fail to do so, the cancellation period extends to 12 months. The notice does not need to be a separate document; it can sit in the quote itself, but it must be clearly legible and not buried in small print at the bottom.

There is one important exception relevant to extension builders. If the customer specifically requests that works begin within the 14-day cancellation period, and they acknowledge in writing that they lose their right to cancel if the works are completed within that period, you can start. In practice, this rarely applies to extensions because groundworks alone take longer than 14 days, but for smaller preparatory tasks such as ordering bespoke materials it matters. If you have ordered a custom bi-fold door on day two of the cancellation period, you need a written request from the customer to justify that spend.

The practical fix is to include a box in your quote that the customer initials, confirming they have received the cancellation notice and, separately, a second box if they are requesting early start. These two boxes take 30 seconds to add and they have saved builders from having to absorb the cost of returned or non-returnable materials.

• •Include the 14-day cancellation notice in the quote document itself
• •Add a customer signature or initials field confirming receipt of the notice
• •Use a separate signed acknowledgement if ordering bespoke materials before the 14 days expire
• •Keep a copy of the signed quote for at least six years (Limitation Act 1980 contract claim window)

Variations: The Clause That Pays for Itself

Every extension job has variations. The customer changes the window size, the ground conditions require deeper foundations, or the plasterer finds a wall that is not where the drawings said it would be. Without a written variation clause, you are negotiating every change from a position of weakness.

Your quote should state that any variation to the agreed scope must be confirmed in writing (email is fine) before the additional work is carried out, and that the price for variations will be calculated at the day-rate specified in the quote, plus materials at cost plus a stated percentage for handling and procurement. In the example above, a reasonable approach would be: day rate £350 per operative per day (eight-hour day), materials at cost plus 15%.

The variation clause should also address what happens if a variation affects the programme. If the customer adds a utility room to the extension after groundworks are already in, that changes the drainage design, the floor screed layout, and possibly the structural calculations. The clause should say, clearly, that variations may affect the completion date and that a revised programme will be issued when the variation is agreed. This prevents the customer later claiming you were late when the delay was caused by their own instruction.

Finally, state that variations will not be carried out until a written variation order is signed. Some builders use a simple one-page variation order form for this. If the customer refuses to sign but verbally instructs additional work, do not proceed. The cost of standing your ground for ten minutes is far less than the cost of unpaid variation work three months later.

• •State your day rate and materials mark-up clearly in the original quote
• •Require written confirmation of every variation before work begins
• •Reserve the right to revise the programme when a variation affects sequencing
• •Never carry out verbal-only variation instructions on a consumer contract

Building Regulations, Building Control, and Competence

An extension requires Building Regulations approval in almost every case. Your quote should state clearly who is responsible for submitting the Building Regulations application and paying the associated fees. Typically, the homeowner commissions and pays for Building Control directly, but on many jobs the builder handles the submission on the customer's behalf. Whichever arrangement you use, write it down.

The Building Safety Act 2022 introduced competence duties that extend to all contractors carrying out building work, not just those working on higher-risk buildings. From 27 January 2026, the Building Safety Regulator operates as an independent statutory body for England and Wales, having transferred from the Health and Safety Executive. The practical effect for sole-trader builders doing extensions is that you must be able to demonstrate competence in the specific works you are carrying out. This is not a new concept, but the regulatory scrutiny has increased and the documentation expectations have grown.

Your quote should reference your relevant qualifications, trade memberships, and insurance. If you are a member of the Federation of Master Builders, the National Federation of Builders, or a similar body, state it. If you are registered with a competent person scheme for any aspect of the works (for example, a FENSA-registered installer fitting the bi-fold door, or a Trustmark-registered contractor), name the scheme and your registration number. These details do not just reassure the customer; they establish a documented record of your claimed competence at the time of quotation.

Building Control inspection stages should also be referenced in the quote, particularly if you are pricing a fixed-cost contract. Delays caused by Building Control unavailability are outside your control. Your programme should note the inspection stages and state that the programme assumes reasonable Building Control turnaround times. If inspections are delayed by the local authority or an approved inspector, the completion date adjusts accordingly.

• •State who submits the Building Regulations application and who pays the fees
• •List relevant qualifications, trade memberships, and competent person scheme registrations
• •Reference Building Control inspection stages in the programme section
• •Include a clause that programme delays caused by Building Control are not the builder's liability

Insurance, Defects Liability, and Warranties

Every quote for an extension should state the insurance cover you carry: public liability (minimum £2 million for most domestic extension work, though £5 million is now the standard requested by many homeowners and mortgage lenders), employers liability if you use any subcontractors or labour-only workers, and contract works (all-risks) cover for the works themselves while they are under construction. List the insurer, the policy number, and the expiry date. A customer who asks to see your certificate of insurance before signing should be encouraged, not deflected.

The defects liability period is the window after practical completion during which you will return to remedy any defects that arise from your workmanship, at no cost to the customer. Twelve months is standard for domestic extension work. State the start and end date clearly once practical completion is certified. During this period, you are not responsible for defects caused by the customer's own actions, fair wear and tear, or works carried out by others after you left site. Those exclusions should be in the quote.

If you are offering a structural warranty, such as a ten-year LABC warranty or a Premier Guarantee, state the product, the provider, and the registration fee (if the customer is paying it). Some builders absorb the warranty fee into the contract price; others charge it separately. Either approach is fine, but it must be transparent in the quote. A customer who discovers after signing that the warranty costs an additional £800 has grounds to feel misled, and under the Consumer Rights Act 2015 a term that creates a significant imbalance in the parties' rights may be considered unfair.

Do not confuse the defects liability period with the statutory limitation period. Under the Limitation Act 1980, a customer has six years from the date of the breach to bring a claim for breach of contract (12 years if the contract is executed as a deed). Your one-year defects liability period is a practical arrangement for returning to site; it does not cap the customer's legal right to bring a claim if a serious structural defect emerges in year four.

• •State public liability cover level, insurer, policy number, and expiry date
• •Specify the defects liability period start date (typically practical completion)
• •List exclusions from the defects liability period (customer damage, third-party works)
• •Distinguish clearly between your defects period and any structural warranty product

Health and Safety Obligations on Extension Sites

For most single-storey domestic extensions, the Construction (Design and Management) Regulations 2015 apply in a limited form. If the project involves more than one contractor (including a subcontractor you bring in), you are the principal contractor and must produce a construction phase plan before work starts. If the project lasts longer than 30 working days with more than 20 workers simultaneously, or exceeds 500 person-days of work, it must be notified to the Health and Safety Executive.

Your quote should state your CDM role and confirm that a construction phase plan will be prepared. It does not need to be a lengthy document for a straightforward extension, but it must address site-specific hazards: ground conditions, existing services, working at height, and waste management. The Work at Height Regulations 2005, Regulation 12, requires that any scaffold or access equipment used on site is inspected before use and at intervals of no more than seven days by a competent person. If scaffolding is part of your quote (as it is in the worked example above), your quote should reference this obligation.

Under the Health and Safety at Work etc. Act 1974, you have a duty to ensure, so far as is reasonably practicable, the health, safety, and welfare of anyone affected by your work, including the homeowner's family and neighbours. For extension sites adjacent to occupied dwellings, this means hoarding or barriers, secure material storage, and clear site rules communicated to the customer in writing. Including a brief site rules summary in your quote or in a separate pre-start letter is good practice and demonstrates competence under the Building Safety Act 2022 framework.

If any excavation work is required (and on a foundation job it will be), you must contact the relevant utility companies before breaking ground and obtain drawings for underground services. The cost of service strike damage is not covered by most standard public liability policies without specific endorsement. State in the quote that the client is responsible for providing any utility drawings they hold, and that you will carry out a STATS search at the client's expense before excavation commences.

• •Confirm CDM role and commitment to preparing a construction phase plan
• •Reference scaffold inspection obligations under Work at Height Regulations 2005, Reg 12
• •Include site rules summary for occupied-dwelling extension sites
• •State responsibility for utility STATS search before excavation

VAT Treatment on Domestic Extension Work

The standard rate of VAT (20%) applies to most new extension work on existing domestic dwellings. This is set out in VAT Notice 708 (Buildings and Construction), published by HMRC. The worked example above prices at 20% VAT throughout, which is correct for a sole trader who is VAT-registered and building a new extension to an existing home.

There are reduced-rate reliefs available in specific circumstances. Works qualifying as a conversion of a non-residential building into a dwelling, or certain works for disabled people under Group 12 of Schedule 8 to the VAT Act 1994, may attract the 5% rate. These are narrow categories and you should not apply a reduced rate without confirming eligibility with your accountant or HMRC. Misapplying a reduced rate on a domestic extension is a VAT error with penalties attached.

If you use subcontractors on the job, the Construction Industry Scheme (CIS) applies. Under the Finance Act 2004 and the Income Tax (Construction Industry Scheme) Regulations 2005, you must verify each subcontractor with HMRC before making the first payment, deduct CIS at either 20% (registered) or 30% (unregistered), and file monthly returns. From 6 April 2026, mandatory nil returns were reintroduced, meaning you must file a return every month even if you made no CIS payments that month. Failure to file attracts an automatic £100 penalty per month.

The 6 April 2026 CIS reform also introduced a 'knew or should have known' supply-chain liability test, aligned with the approach taken in VAT fraud cases (specifically the Kittel principle from EU VAT law, retained in UK practice post-Brexit). This means that if a subcontractor you engage turns out to be fraudulent and has not accounted for tax, HMRC can pursue you as the contractor if they determine you knew or ought to have known about the non-compliance. Verifying subcontractors through the HMRC CIS online service and keeping the verification references in your records is not optional; it is your primary defence against this liability.

• •Charge 20% VAT on standard domestic extension work (VAT Notice 708)
• •Do not apply reduced rates without confirming eligibility in writing with HMRC or your accountant
• •Verify every subcontractor with HMRC CIS before the first payment and retain the verification reference
• •File monthly CIS returns even in months with no subcontractor payments (mandatory nil returns from April 2026)

Common Mistakes on Extension Quotes and How to Fix Them

The most common mistake sole-trader builders make on extension quotes is quoting a lump sum with no breakdown. A lump-sum quote feels simpler to produce, but it gives you no protection when the customer asks why the bi-fold door costs what it does, or queries why the scaffolding is on the invoice when they thought it was included. A line-by-line breakdown, as in the worked example above, takes longer to produce once and saves hours of dispute later.

The second most common mistake is omitting an expiry date. Material prices and subcontractor rates change. A quote with no expiry date can, in theory, be accepted six months after you issued it, by which point your timber prices may have risen 15% and your plasterer has moved to a different rate. A 30-day validity period, as used in the example, is standard. If the customer comes back after 30 days, you reissue a revised quote. That is a normal and professional conversation.

Failing to specify who is responsible for Building Control fees is a perennial source of disputes. Some customers assume the builder handles everything; others assume they pay separately. Neither assumption is safe without it being written down. State it explicitly: 'Building Regulations application fee and Building Control inspection fees are the responsibility of the client and are not included in this quotation.'

Provisional sums presented as fixed prices are another common error. If you are not certain what the drainage connection will cost because you have not seen the CCTV survey, say so. Write it as a provisional sum with an allowance figure, and state the basis on which the final cost will be calculated. Customers generally accept genuine uncertainty when it is explained honestly upfront. What they do not accept is discovering that a line item they thought was fixed turns out to be a guess.

• •Always provide a line-by-line breakdown, not a lump sum
• •Include an expiry date (30 days is standard)
• •State explicitly who pays Building Control fees
• •Label provisional sums clearly and separately from fixed-price items
• •Include the customer's full address and your own UTR and VAT number on every quote

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