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Extension Scope of Works: What to Include and How to Write It

What an extension scope of works should contain, how it differs from a schedule of works, and the build sequence, timings and checks to agree before work starts.

The Extension Works 8 November 2026
Extension Scope of Works: What to Include and How to Write It

Extension Scope of Works: What to Include and How to Write It

Extension scope and drawings on a dining table

A scope of works for a home extension is a written description of exactly what the builder will do, to what standard, and what is left out. A schedule of works is the itemised list of tasks that sits underneath it, usually in building sequence, so that every contractor prices the same job. Get both down in writing before you sign and you avoid most of the arguments that sour extension projects: unclear allowances, surprise extras and disputes about what was ever included.

This guide shows what to put in each document, the order the work normally runs in, how long each stage typically takes, and what to check before you agree.

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TL;DR

  • A scope of works says what is being built and delivered. A schedule of works lists the tasks to be priced, normally by trade or in build order.
  • Cover drawings, every trade from groundworks to decoration, materials, who supplies what, allowances, exclusions and handover documents.
  • Permissions (Permitted Development or planning, Building Regulations, Party Wall) must be dealt with before the relevant work starts, so put them in the scope.
  • Ask for stage payments, start and finish dates, delay arrangements and a joint snagging list in the contract.
  • Our fixed-price, in-house service builds all of this into one package for single-storey rear extensions.

Table of Contents

Scope of works vs schedule of works

The two terms overlap, and the industry does not use them in one fixed way. Local Authority Building Control’s Front Door describes a scope of work as the written description of the work expected under the contract. It can be a broad description or a comprehensive account covering the project, materials, finishes, milestones, programme, pricing, responsibilities and the end product.

The NBS describes a schedule of work as a list of building work, in outline or in detail, that must be unambiguous and cover at least in outline everything for which prices are required. It is normally read alongside drawings, product schedules, specifications and preliminaries.

In practice, for a homeowner:

Document Answers the question Typical content
Scope of works What am I getting? Project overview, size and layout, drawings, finishes, responsibilities, exclusions, handover
Schedule of works What tasks make it up, and in what order? Itemised tasks by trade or stage, quantities, materials, provisional items
Specification To what standard? Product types, performance, workmanship quality
Programme When does each thing happen? Durations, start and finish dates, dependencies

If your builder gives you one combined document, that is fine, provided each of those four questions is answered somewhere in what you sign.

What a good extension scope of works includes

Write the scope so that a stranger could read it and know what will be standing in your garden at the end. For a single-storey rear extension, work through these headings.

Project overview and drawings

Start with a plain description: the size of the extension, where it attaches to the house, roof type, and what the new space is for. Reference the drawing numbers and revisions the price is based on. If drawings and the written scope disagree, the contract should say which one wins, and the conflict should be raised before work is priced, not discovered on site.

Structural design belongs here too. If a wall is being opened up, the scope should refer to the structural calculations and the beam or steel sizes they specify. Our guide to structural calculations for extensions explains what they cover and why the building inspector asks for them.

Trade-by-trade sections

A workable schedule typically runs through the following, each with its own short description of what is included:

  1. Site set-up and protection: hoarding or fencing, protecting floors and the existing house, welfare arrangements, skip and waste removal.
  2. Demolition and strip-out: removing the existing rear wall sections, doors, windows, conservatory or outbuildings in the way.
  3. Groundworks and foundations: excavation, concrete, drainage alterations, spoil removal.
  4. Structure: masonry or timber frame, steel beams, lintels, insulation within the wall, damp-proof course.
  5. Roof: structure, covering, rooflights, flashings, guttering.
  6. External joinery: windows, bi-fold or sliding doors, fascias.
  7. First fix: electrics, plumbing, heating pipework, any ventilation.
  8. Plastering and making good.
  9. Floor finishes and tiling.
  10. Second fix: sockets, switches, radiators, internal doors, skirting.
  11. Kitchen and bathroom fit-out, if part of the job.
  12. Decoration.
  13. External works: patio edges, making good the garden, boundary repairs where affected.

Materials, products and who supplies what

Name the product or give a clear specification and an allowance. If you are supplying the kitchen, tiles or light fittings yourself, say so, and say who fits them and who is responsible if they arrive late or damaged. Guidance from specification writers generally also expects testing, certificates, warranties, waste handling and site protection to be stated rather than assumed.

Exclusions, assumptions and provisional items

This is the section that saves money. List separately:

  • Exclusions: anything not included, such as redecorating the existing rooms or relocating a boiler.
  • Assumptions: for example, normal ground conditions or access for materials.
  • Provisional items: work that cannot be priced exactly yet, shown with an allowance that is adjusted once the real cost is known.
  • Clarifications required: questions that must be answered before the price is final.

If a price is quoted as fixed, ask what it assumes. The stronger the list of assumptions, the less room there is for a variation later.

Handover and completion

The scope should end with what you receive: a joint snagging list, a builder’s clean, product warranties and certificates, and the Building Regulations completion certificate. RICS notes that Building Regulations cover structural safety, fire risk, energy efficiency and ventilation, and that a missing completion certificate can cause problems when you sell, insure or remortgage. Our article on getting a completion certificate for an extension covers the process in more detail.

Four items to receive at extension handover

The build sequence your schedule should follow

Most schedules are easiest to read when they follow the order of work on site. Homebuilding’s extension planner sets out a logical sequence that works well as a backbone for a rear extension:

  1. Stabilise and make safe.
  2. Strip out and salvage.
  3. Treat any problems found.
  4. Carry out structural work.
  5. Make the shell weather-tight.
  6. Complete first fix.
  7. Plaster and make good.
  8. Lay fixed flooring and tiles.
  9. Complete second fix.
  10. Decorate.
  11. Snag and reach practical completion.

The same source says a programme should also show timescales, lead times, phases and durations, and can include budgets and cashflow. That matters because a schedule of works lists what is done, while a programme shows when. Ask for both, or a schedule with durations built in.

How long each stage usually takes

Timings vary with size, ground conditions and access. Homebuilding’s guidance gives these indicative figures, which are useful for sense-checking a programme:

Stage Indicative duration
Design At least two months; often two to three months for a new or complex project
Planning At least three months
Building Regulations approval Around two weeks
Tendering About one month, plus another month before the builder starts
Foundations Up to a week, or a couple of weeks in difficult conditions
Watertight shell Two to three weeks, sometimes four
First fix Two to three days on a simple job; four to six weeks on a larger one
Second fix Four to six weeks
Finishes Six to eight weeks
Snagging About one month

The same guidance notes that ground conditions, access, weather, complexity, inspections, design changes and late materials can all stretch these periods. Build a little float into your own plans, and agree in the contract what happens if the finish date slips.

Permissions to account for before work starts

Put the permissions route in the scope, with who is responsible for each one.

Planning or Permitted Development. Many single-storey rear extensions can go ahead under Permitted Development, but the rules on size and height are specific. GOV.UK’s technical guidance says Permitted Development does not remove Building Regulations or Party Wall Act requirements. Larger single-storey rear extensions go through a neighbour-consultation route and cannot start until the relevant conditions are met, or 42 days have passed without a decision. Our Permitted Development checklist and the guide to the 4m and 3m height and depth limits walk through the details. If your property is listed or in a conservation area, RICS advises checking for extra restrictions through the Planning Portal or your local authority. For a plain-English overview of what you can build without planning permission, see this guide to Permitted Development rules.

Building Regulations. GOV.UK explains that a full-plans application normally gets a decision within five weeks, or two months with your consent. A building notice lets work start two days after submission but gives no formal advance approval. Whichever route is used, the scope should list the inspection stages. Our piece on building control inspections explains what to expect on site.

Party Wall Act. Where it applies, the National Home Improvement Council says notices should generally be served one or two months before the relevant work, and you need the neighbour’s written agreement or a Party Wall Award before starting. Add this lead time to your programme so it does not become a delay.

Fees. Application fees are separate from the build price, so state who pays them. See planning fees for an extension for what to budget.

Permissions to account for before work starts

Recording changes, delays and sign-off

Even a careful scope will meet surprises. Decide in advance how they are handled:

  • Variations: any change to the scope is agreed in writing with the price and time effect before the work is done.
  • Provisional items: state the allowance and how the final figure is confirmed.
  • Delays: record the agreed start and finish dates and the arrangement if either moves.
  • Drawing conflicts: the builder raises any mismatch between drawings and schedule before pricing.
  • Completion: the extension is complete when the snagging list is cleared and the certificates and warranties are handed over.

Checks before you agree the schedule

Citizens Advice says a written contract should cover what you are paying for, timings including start and finish dates and what happens with delays, tidying and rubbish or skips, materials, equipment, subcontractors and payment. It also recommends paying in stages rather than all upfront.

A quick read-through checklist:

  1. Does the scope describe the finished result, not just a list of trades?
  2. Are drawings and structural calculations referenced by revision?
  3. Is the price clear on what is fixed and what is provisional?
  4. Are exclusions written down?
  5. Are permissions and fees assigned to a named party?
  6. Are start date, finish date and delay arrangements stated?
  7. Are stage payments linked to completed stages?
  8. Does handover include certificates, warranties and a snagging process?

Our view on scopes of works

Most extension disputes we hear about start with a vague scope: a price given before anyone has agreed what is in it, then a string of extras. We built The Extension Works to remove that gap.

Our service covers design, planning, structural calculations, building control and construction for single-storey rear extensions, managed by one in-house team. Because the same team draws it, prices it and builds it, the scope is not passed between a designer, an agent and a builder, which is where details tend to go missing.

You get a fixed VAT-inclusive price, a live 3D model so you can see the extension before you commit, no sales visits, a dedicated team for your project and a 12-month workmanship warranty. We think a scope should be something you can see and understand, not a document you have to decode.

Esskay

Get a fixed price for your rear extension

If you are planning a single-storey rear extension, we can turn your scope into a fixed VAT-inclusive price online. You design it with live 3D modelling, see the price instantly and book online. Booking carries a one-off booking fee of £499, and design, planning handling, structural calculations, project management and construction are then managed by our in-house team.

The Extension Works

Try the instant extension quote tool to see what your extension could look like, or read about our single-storey rear extension service. We cover Sutton, Morden and nearby areas of London and the South East.

FAQ

Do I really need a scope of works for a small extension?

Yes. Even a simple rear extension involves many trades and decisions, and a written scope makes sure everyone prices and builds the same thing. It can be as short as a page or as detailed as a full itemised schedule, depending on the project.

Is a schedule of works the same as a build programme?

No. A schedule lists the work items to be priced, usually by trade or build order. A programme is time-based and shows when each task happens, how long it takes and what depends on what. You want both, even if they sit in one document.

Who writes the scope of works?

It is usually prepared by your designer, architect or contractor, based on the drawings. With a design-and-build service such as ours, the same team prepares the drawings, price and build, so the scope and the price stay aligned.

What should I do if the work changes during the build?

Agree every change in writing before it is carried out, with its cost and effect on the finish date. Provisional items should have a stated allowance so you know the likely range from the start.

Sources