Extension invoice template UK (2026): side returns, CIS and VAT

A house extension invoice has to explain fabric work on the ground — foundations, masonry, steels, roof, windows, first and second fix, scaffold, Building Control and Party Wall interfaces — not a vague “extension done” line. “Extension as agreed” does not tell a householder whether a side-return, rear single-storey, two-storey or wraparound package was included. It does not tell a main contractor’s QS which plot, purchase order or package to release. It does not tell a CIS contractor how much is labour and how much is the direct cost of concrete, blocks, steels, roof covering, windows and insulation you paid for.

The payer and the operation both matter. An extension builder billing a private householder for work on their own home sends a normal invoice: no CIS. The same builder billing a main contractor, developer or refurbishment principal for construction operations can be inside CIS. Alteration, repair or extension of a building typically sits under construction operations in CISR14100 / Finance Act 2004 section 74(2)(a). When extension works form part of a wider preparatory or finishing package that brings construction to completion, CISR14240 (preparatory, integral and finishing operations — including scaffolding, insulation as part of a wider project, and certain fittings) is also relevant. Private householders are not CIS contractors — see the public CIS overview.

VAT is separate. If you are VAT-registered, an ordinary side or rear extension on an occupied existing dwelling is usually standard-rated at 20%. The internet myth that home extensions are “VAT free” is wrong for the typical lived-in house. A reduced 5% rate can apply only when the conditions in VAT Notice 708 are met — for example certain residential conversions that change the number of dwellings, qualifying empty-home renovations, or non-residential to dwelling conversions. Soften absolute claims; check Notice 708 and your VAT adviser. Architect, surveyor and consultant fees are usually standard-rated even when some construction services are reduced-rated.

This guide gives copy-paste fields, a labour/materials split for extension packages, deposits and stages for multi-week jobs, four worked examples and a practical treatment of CIS, VAT and domestic reverse charge. Figures are illustrative only, not UK market rates or a price list. InvoiceAdept does not decide CIS or VAT status and does not file CIS300, VAT returns, Making Tax Digital updates or Self Assessment to HMRC. It does not issue Building Control completion certificates, Party Wall awards or planning permissions.

Related templates: builder, bricklayer, scaffolder, carpenter, electrician, plumber, loft conversion, deposit invoice, domestic reverse charge and how to invoice a UK client as a tradesperson. This page focuses on house / home extensions — side returns, rear single-storey, two-storey and wraparounds — not loft conversions or stand-alone carpentry.

Rules and links were checked for this guide on 5 September 2026. General information only, not tax, legal, Building Regulations, Party Wall or planning advice. InvoiceAdept is from Tech Me Today Ltd, Companies House 15917255, ICO ZB944663.

In short

Start by identifying who pays you, what extension type you built, and whether the job alters or extends a building under a construction contract.

Private householder, own-home extension: no CIS. The householder is not a CIS contractor. If VAT-registered, an ordinary side / rear / wraparound extension at an existing lived-in home is usually 20%. Show foundations, masonry, roof, windows, first and second fix, scaffold and finishes clearly. Do not claim “VAT free” because it is an extension.

Extension package for a CIS contractor: typically within CIS when a contractor pays you for construction operations that alter or extend buildings (CISR14100). Cite CISR14240 when works sit inside a wider finishing or preparatory package (scaffold, insulation as part of the project). Split labour from materials at direct cost (CISR15060 / CISR15090).

Manufacture and delivery of materials only (no install): generally outside CIS (CISR14220). A mixed contract with any install can pull the whole contract into CIS (CISR14020 mixed-contract manuals).

VAT reduced rate (5%): only when Notice 708 conditions are actually met — change in number of dwellings, qualifying empty-home renovation (typically empty 2+ years), or non-residential conversion. Ordinary side or rear extensions on an occupied house stay 20%. Never reverse-charge a householder. Never invent 0% for a normal extension.

Take a deposit before ordering steels, windows, roof materials or kitchen carcasses if your terms require one. Number and invoice that deposit. Then use recognisable stages: groundworks / foundations, weathertight shell, first fix, second fix / snag. Keep variations for extra bi-folds, roof lanterns, steel upgrades or kitchen adds separate from the agreed package.

Use the invoice generator for a first invoice. InvoiceAdept Free is £0 for five invoices per month. Pro is £7.99 excl VAT and includes WhatsApp send. Pro+ is £12.99 excl VAT and includes CIS. Stripe’s own fees apply (UK cards 1.5%+20p), but InvoiceAdept adds no platform fee.

Who this extension invoice template is for

This template is for UK extension builders, general builders who deliver house-extension packages, and subcontractors who dig, brick, roof, or finish extensions and need readable invoices for householders, landlords, builders and housing clients. It covers the paperwork pattern, not a price list and not a Building Control or Party Wall document.

• Extension specialists (side-return, rear single-storey, two-storey, wraparound)

• Builders offering house-extension packages as a defined product

• Groundworkers and foundation crews billing extension footings and slabs

• Bricklayers and blocklayers building extension walls

• Roofers closing extension roofs and abutments as part of a package

• Joiners fitting bi-folds, roof lanterns and internal joinery

• Subcontractors to main contractors on residential extension packages

• Sole traders and limited companies who need CIS and VAT lines that match the payer

If your day job is loft conversions, stand-alone scaffolding hire or full new-build houses without an extension focus, use the related loft, scaffolder or builder guides and come back here for the extension-specific lines.

Three extension jobs, three invoices

These three jobs can use similar foundations and masonry but need different invoice logic.

A main contractor can be the CIS contractor even when the finished extension serves a tenant or homeowner. If the builder engages you, your invoice is to that builder. That contractor-to-subcontractor payment is the one to test. If the householder hires and pays you directly, the householder invoice has no CIS.

What extension work belongs on the invoice

Do not compress a multi-week extension into “supply and build extension”. Describe foundations, shell, weatherproofing, services and finishes, and what another firm supplied.

Extension types to name clearly on the face of the invoice

What a UK extension invoice must include

UK invoices need the basics HMRC and customers expect. See GOV.UK invoicing guidance. For VAT-registered traders, VAT invoices need the extra fields in that guidance and your VAT registration number.

VAT registration threshold is £90,000 (see VAT registration). Do not use outdated £85,000 figures. Deemed contractor status for CIS turns on construction spend of more than £3 million in the relevant period — never quote £1 million as the current threshold.

Copy-paste extension invoice fields

Use this as a checklist when building the invoice in software or on paper.

Invoice number: EXT-2026-00XX
Invoice date:
Tax point (if different):

From:
[Trading name]
[Address]
[Phone / email]
[VAT number if registered]
[Company number if limited — e.g. Tech Me Today Ltd style]

Bill to:
[Householder OR contractor company name]
[Site address / plot / PO]

Job reference / quote number:
Property / extension type: [side-return | rear single-storey | two-storey | wraparound | other]
Rooms created / opened: [kitchen-diner / utility / bedroom / bathroom]
Steel schedule ref:
Drawing / Building Control ref:

Line items:
1. Survey / structural / access / scaffold — £…
2. Demolition / strip-out and preparation — £…
3. Groundworks and foundations — materials at direct cost £… ; labour £…
4. Oversite / slab / floor structure — £…
5. Steels and structural connections — materials £… ; labour £…
6. Masonry / walls and openings — £…
7. Roof structure, covering and weatherproofing — £…
8. Windows / doors / bi-folds / lantern — materials £… ; fit labour £…
9. Insulation, plasterboard, first fix — £…
10. Second fix / kitchen / snag — £…
11. Variation [ref] — £…
Less: Deposit credit INV-… — (£…)
Less: CIS deduction (if applicable) — (£…)
VAT (or reverse charge statement) — £…
Amount due — £…

Payment: bank details / Stripe
Due date:
CIS: UTR … Verification … Rate 20% / 30% / 0% gross (contractor jobs only)
Building Control: fee charged separately / by client — ref …
Party Wall: award PW-… issued separately / by surveyor

Sole trader versus limited company

InvoiceAdept supports both patterns. It does not file your CIS300 or VAT return either way.

Labour versus materials for extension CIS

For CIS, materials at direct cost can be excluded from the deduction base (CISR15060 / CISR15090). Mark-up is not materials. Free-issue steels, windows or blocks from the contractor are not your materials — note them as free-issue so you do not claim them in the materials exclusion.

CIS deep dive: extensions as building alteration

Prefer CISR14100 as the primary cite when you alter, repair or extend a building by constructing a house extension — Finance Act 2004 s74(2)(a). Digging foundations, building masonry, inserting steels, forming a roof and weatherproofing abutments are fabric works, not a soft service.

Cite CISR14240 when extension works sit inside preparatory or finishing operations that bring a wider construction project to completion — for example scaffolding erected for the extension package, or fitting thermal insulation as part of the wider project.

CISR14220 generally keeps manufacture and delivery of materials without installation outside CIS. If your contract mixes supply with any install, mixed-contract rules can bring the whole payment into CIS — see CISR14020.

CIS deduction rates for subcontractors: 20% if verified, 30% if unverified, 0% with gross payment status. Show the rate and verification outcome the contractor applied. InvoiceAdept can help format CIS lines on Pro+; it does not file the contractor’s CIS300.

VAT: the “VAT free extension” myth versus Notice 708

Keep three buckets clear. Soften absolute claims; your VAT adviser and VAT Notice 708 win over blog wording.

Architects, surveyors, consultants and supervisors are usually standard-rated even when some construction services on the same project are reduced-rated. Do not bundle professional fees into a 5% claim without checking.

Also check Notice 708 for zero-rating on qualifying new dwellings — that is not the normal occupied-home extension case. An ordinary side-return kitchen-diner on a lived-in terrace is not “VAT free”. VAT registration threshold remains £90,000.

Domestic reverse charge

Domestic reverse charge may apply when all of these hold: both parties VAT-registered; the supply is construction services reported within CIS; the rate would otherwise be standard or reduced (not zero); and the customer is not an end user. Never reverse-charge a private householder. See InvoiceAdept’s domestic reverse charge invoice guide.

Scaffold, steel, brickwork and specialist trades on the invoice

Extension jobs almost always need access and often a steel delivery. How you show those lines changes clarity and sometimes CIS/VAT paperwork.

Deposits and staged payments for extension packages

Extension jobs burn cash on foundations, steels, windows and scaffold weeks. If your terms require a deposit, raise a numbered deposit invoice before ordering stock, then credit it on stage or final invoices. See the deposit invoice template.

Figures for deposit percentages are commercial choices — mark them illustrative only when you show examples. Do not invent “industry standard” percentages.

Variations and retention

Extra bi-folds, roof lanterns, steel section upgrades after opening-up, Party Wall delays that extend scaffold weeks, kitchen upgrades, or client-driven layout changes should be written variations referencing the original quote — not silent increases on the final total.

If 5% retention is held to practical completion or end of defects on a contractor package, show retention withheld and later retention released on separate lines so cash collected matches the certificate. Do not bury retention inside a vague “balance” line.

For householders, keep consumer-friendly stage language. Do not paste commercial retention machinery onto a domestic extension unless the written contract actually uses it.

Worked examples A–D

All money figures below are illustrative only. They are not market rates, quotes or a price list.

Example A — domestic side-return for a householder (20% VAT)

Private householder; side-return single-storey kitchen-diner; no CIS.

No CIS block. Deposit of £6,000 (illustrative) would appear as a separate numbered invoice then as a credit on stage or final invoices.

Example B — contractor rear-extension package (CIS 20%, reverse charge)

VAT-registered subcontractor to VAT-registered main contractor; rear single-storey finishing package; CIS verified 20%; reverse charge applies (illustrative assumption that tests are met).

Show UTR, verification and reverse-charge wording clearly.

Example C — empty-home renovation extension (CIS; VAT depends)

Housing contractor pays for an extension within a property empty for 2+ years. CIS typically applies (CISR14100). VAT: only if Notice 708 empty-home renovation conditions are met might 5% apply; otherwise treat as standard-rated and take advice. This example shows a labour/materials split for CIS without asserting the VAT rate.

State the VAT treatment your adviser confirms on the face of the invoice.

Example D — materials-only steel delivery, no install

Supply of RSJs to site; no erection. Generally outside CIS (CISR14220). Usually standard-rated VAT if you are registered.

If a later variation adds erection labour under the same contract, revisit mixed-contract CIS rules (CISR14020).

Building Control, Party Wall and planning — the invoice is not a certificate

An invoice is a request for payment and a commercial record. It is not:

• a Building Control completion or final certificate

• a Party Wall Act award

• planning permission or lawful development confirmation (including permitted development assumptions)

• an electrical Part P / competent person notification

• structural engineer sign-off (unless that professional issues their own document)

If you collect a Building Control fee from the client, show it as a clear disbursement or fee line with the receipt reference. Do not imply the invoice itself is the approval. If Party Wall notices or awards are handled by a surveyor, keep that paperwork separate and optionally reference award numbers on the invoice (“Party Wall award PW-… issued separately”). Neighbour disputes and access licences are legal matters — not invoice line items that prove consent.

Late payment (brief)

The Late Payment of Commercial Debts (Interest) Act 1998 is a B2B regime, not an automatic right against private householders. For qualifying commercial debts, statutory interest is Bank Rate plus eight percentage points under SI 2002/1675. Bank Rate was held at 3.75% on 30 July 2026, so the statutory rate is 11.75% a year for interest periods while that Bank Rate applies. The next Bank of England decision referenced for context is 17 September 2026. Fixed compensation bands are £40, £70 or £100 according to debt size.

Do not paste those commercial words onto a consumer householder invoice. Use fair consumer terms agreed before work, a clear due date and proportionate reminders.

Making Tax Digital means records, not filing

InvoiceAdept creates and stores invoice records. It does not file VAT returns, CIS300, MTD updates or Self Assessment to HMRC. It does not decide whether an extension package is standard- or reduced-rated. It does not submit Building Control notices or Party Wall paperwork.

MTD for Income Tax Self Assessment phases in by turnover: over £50,000 from 6 April 2026; £30,000 from April 2027; £20,000 from April 2028. InvoiceAdept keeps records; it does not submit quarterly updates.

How InvoiceAdept helps extension builders

InvoiceAdept helps turn a quote and stage history into readable invoices without claiming to be HMRC software or a Building Control platform.

You can separate survey, scaffold, foundations, steels, masonry, roof, windows, materials, deposits and variations; send the PDF; and offer Stripe payment where enabled. InvoiceAdept adds no platform fee to Stripe, though Stripe’s own fees apply (UK cards 1.5%+20p). See pricing, CIS invoice features and start from the invoice generator.

Quote versus invoice versus retention on contractor packages

A quote is an offer. An invoice is a request for payment against agreed or certified work. Retention is a contract term, not a tax rule.

Mistakes that bounce extension invoices

FAQ

Does a house extension come under CIS?

Often yes when a CIS contractor pays you for work that alters or extends a building. Prefer CISR14100. Use CISR14240 when extension works are part of a preparatory or finishing package. A private householder paying you directly is not a CIS contractor.

Does a householder deduct CIS from an extension builder?

No. A private householder is not a CIS contractor. Domestic extension invoices should not carry CIS deduction blocks.

Are side-return and rear extensions within CIS for contractor jobs?

Typically yes when a contractor pays for alteration or extension of buildings (CISR14100), or as finishing/prep within a wider package (CISR14240). Split labour and materials; show UTR and verification as your process requires.

What if I only supply steels, blocks or windows with no installation?

Manufacture and delivery without installation is generally outside CIS (CISR14220). Mixed contracts that also include install need careful reading of the mixed-contract rules (CISR14020).

What can I treat as materials for CIS on an extension job?

The direct cost of materials you paid for on that contract — concrete, bricks, blocks, steels, windows, insulation, plasterboard, fixings — supported by evidence (CISR15060 / CISR15090). Mark-up is not direct-cost material. Free-issue materials from the contractor are not your materials.

Is a house extension VAT free in the UK?

Usually no. An ordinary side or rear extension on an occupied existing home is typically standard-rated at 20% if you are VAT-registered. The “VAT free extension” claim is a common myth for that case.

When can extension works be 5% VAT?

Possibly when Notice 708 conditions for a qualifying residential conversion, empty-home renovation (typically empty 2+ years), or non-residential to dwelling conversion are met. Soften absolute claims; document the facts and take VAT advice. A kitchen-diner or bi-fold alone does not create a 5% claim on an occupied house.

When does reverse charge apply to extension invoices?

When the domestic reverse charge tests are met: both parties VAT-registered, the supply is construction services reported within CIS, standard or reduced (not zero), and the customer is not an end user. Never reverse-charge a householder. See the DRC invoice guide.

Should I invoice a deposit before ordering steels, windows or concrete?

If your terms require a deposit, yes — raise a numbered deposit invoice, then credit it on stage or final invoices. See the deposit invoice template.

How should I invoice an extra bi-fold, roof lantern or kitchen upgrade?

As a written variation referencing the original quote, not as a silent increase on the final total.

How should scaffold appear on my extension invoice?

If you hired it, show a clear access/scaffold line with ticket and period. If a scaffolder bills separately, note “scaffold by others”. See the scaffolder invoice template.

Does InvoiceAdept file CIS, VAT or MTD returns, or issue Building Control / Party Wall certificates?

No. It creates and stores invoices. CIS features are on Pro+ at £12.99 excl VAT; Pro is £7.99 excl VAT with WhatsApp send; Free is five invoices per month. It does not file CIS300, VAT returns, MTD updates or Self Assessment and does not decide tax status. It does not issue Building Control certificates, Party Wall awards or planning permissions.

What CIS rates should appear if the contractor deducts?

20% verified, 30% unverified, or 0% with gross payment status — whatever verification outcome applies. InvoiceAdept does not verify you with HMRC.

Is the VAT registration threshold still £90,000?

Yes — £90,000. Do not use £85,000. Deemed contractor construction spend is more than £3 million, not £1 million.

Related guides

• Builder invoice template UK

• Bricklayer invoice template UK

• Scaffolder invoice template UK

• Carpenter invoice template UK

• Electrician invoice template UK

• Plumber invoice template UK

• Loft conversion invoice template UK

• Deposit invoice template UK

• Domestic reverse charge invoice UK

• How to invoice a client UK tradesperson

Pricing · CIS invoices · Invoice generator

About this guide

Written for UK extension builders and subcontractors who need householder and contractor invoices that survive QS review and CIS/VAT scrutiny. Last reviewed 5 September 2026. Canonical URL: https://invoiceadept.com/blog/invoicing/extension-invoice-template-uk/.

General information only — not tax, legal, Building Regulations, Party Wall or planning advice. InvoiceAdept is a product of Tech Me Today Ltd, Companies House 15917255, ICO ZB944663.

Bottom line

Name the extension type, foundations and openings. Split labour and materials for CIS. Keep householder invoices free of CIS. Treat VAT carefully — ordinary occupied-home extensions are usually 20%, not VAT-free; 5% only when Notice 708 conditions truly apply. Use deposits and variations for multi-stage packages. InvoiceAdept helps you issue the paperwork; it does not file HMRC returns or issue certificates.