House extension planning checklist for UK homeowners

The short answer

Before starting a house extension, write down what you want to achieve, check the property and any restrictions, understand which permissions and technical approvals may apply, and prepare enough information for builders to price the same work. This checklist follows the journey from early ideas to construction and handover. Planning and Building Regulations rules differ across the UK, so check the requirements for your nation and property rather than treating any online checklist as an approval.

Key points

Describe the rooms, layout, budget, priorities and compromises you can accept before choosing a design.
Check property boundaries, previous extensions, drainage, access and any planning restrictions.
Planning permission, Building Regulations approval and party wall matters are separate questions.
Ask for appropriate measured drawings, structural information and a defined scope before comparing quotations.
Agree how variations, payments, records, inspections and handover documents will be handled before work starts.

Published by Kezariq Ltd. See the source links below for official guidance.

1. Define the extension you need

Start with the outcome, not a drawing. Is the goal a larger kitchen, accessible ground-floor living, an extra bedroom or improved circulation? Note the rooms you want, how you will use them and what existing spaces need to change.

Set a working budget with room for design fees, approvals, surveys, temporary arrangements and unexpected work. Early cost ranges are not contractor quotations. Do not make commitments based solely on an online estimate.

List essential requirements separately from features you would like if the budget permits.
Decide whether the home will remain occupied during the works.
Record any known issues such as damp, poor access, existing drainage runs or a previous extension.

2. Check the property and planning position

Look at the property type, original house, previous additions, boundary positions and any local designations. Some extensions can fall within permitted development rights; others require an application. The rules and processes vary between England, Wales, Scotland and Northern Ireland.

Check your local planning authority's guidance, relevant conditions and the Planning Portal or national planning service. An online assessment can help organise questions, but it cannot confirm lawful development or grant permission.

Identify the intended extension's position and approximate footprint.
Check whether the property is listed, in a conservation area or subject to an Article 4 direction or planning condition.
Investigate whether the proposal affects neighbours or a shared wall, structure or boundary.
Ask the appropriate authority or qualified adviser when the planning position is uncertain.

3. Plan the technical information and approvals

Planning permission and Building Regulations are different. Most house extensions involve Building Regulations requirements even when a planning application is unnecessary. Structural design, insulation, ventilation, fire safety, drainage and electrical work may all need attention.

Depending on the site and design, you may need measured drawings, structural calculations, ground investigation or drainage information. Identify who is responsible for design, approval applications, inspections and the documents needed at completion.

Confirm the appropriate Building Control route and inspection arrangements.
Consider utilities, surface water drainage and any existing manholes before finalising the layout.
Check whether the Party Wall etc. Act 1996 applies in England or Wales; other nations use different legal frameworks.
Use appropriately competent designers, engineers and contractors for work beyond your own expertise.

4. Prepare a defined scope before asking builders to price

A sketch and a short description rarely give every builder the same basis for pricing. Prepare a set of drawings and a written specification that describes what is included, the materials or performance required, and what remains to be decided.

Ask builders to identify exclusions, provisional sums, assumptions and any items that still need design decisions. Compare quotations against the same scope, not just the lowest total.

Record demolition, foundations, structure, roof, windows, doors, services and finishes.
State which party supplies kitchen units, sanitaryware, flooring and other selected products.
Check insurance, relevant experience, references and who will supervise the site.
Document the proposed programme, payment stages, variations procedure and contractual responsibilities.

5. Prepare for work, changes and handover

Before work begins, agree site access, working hours, protection of occupied rooms, waste removal and how decisions will be recorded. A construction programme can show the sequence of tasks, but actual dates depend on approvals, availability and site conditions.

Keep a record of changes and agreed costs. At handover, collect the relevant Building Control completion documentation, certificates, test results, warranties, operating information and a written snagging list where appropriate.

Confirm who coordinates inspections and makes sure work is not covered up before required checks.
Record variations and approvals in writing before affected work proceeds.
Keep dated progress notes, photographs and payment records.
Download and retain copies of the final records and documents yourself.

Things to check

What do I need the extra space to achieve, and what is my maximum working budget?
What is the property type, and have previous works or local restrictions affected its planning rights?
Who will confirm planning and Building Regulations requirements for this specific address?
Are the drawings, structural requirements and written scope sufficient for comparable quotations?
Have we agreed a written contract, payment stages, programme, change control and site responsibilities?
Who will hold copies of inspection records, completion documents, warranties and the snagging list?

Common questions

Where should I start when planning a house extension?

Start with the space you need and the budget you can afford, then check the property and planning constraints. Work up drawings, technical information and a written scope before inviting detailed quotations.

Do all house extensions in the UK need planning permission?

No. Some qualify under permitted development rights, depending on the nation, type of property and proposed work. Other extensions need an application. The local authority or relevant adviser should confirm the position for your property.

Is Building Regulations approval the same as planning permission?

No. Planning concerns the acceptability of the development, while Building Regulations set technical requirements for building work. Most extensions require Building Regulations involvement even if no planning application is needed.

When should I ask builders for quotations?

You can seek early budget guidance at concept stage, but comparable fixed-scope quotations are easier when builders receive consistent drawings, a written scope and the key technical information.

Start by recording the details of your proposed extension

Use the KEZARIQ assessment to organise what you know about the property and the work you want to carry out. A limited preview is available without payment; the optional detailed Assessment Project Report supports your next steps. KEZARIQ does not grant permissions, certify work or replace specialist advice.

Assessment Project Report — £10.99

Start your extension assessment

Free limited preview. No payment needed to read your preview. The full report is optional.

Important

This guide is general information for UK homeowners. It is not legal, planning, structural or professional advice, and it does not take account of your individual circumstances. Rules change and vary between England, Wales, Scotland and Northern Ireland, and by local authority.

KEZARIQ provides guidance and documents you complete and review yourself. It does not manage your project, carry out professional services, or replace an architect, surveyor, structural engineer, planning consultant or other competent professional where one is required. Nothing here guarantees planning permission, Building Regulations approval, prices, contractor performance or any project outcome. You remain responsible for your own project and decisions.