Extension Feasibility Checker
Seven short questions about your home and your plans. BuildGuide turns them into a clear, plain-English read on planning permission, permitted development, building regulations and the Party Wall Act.
Before you start
Most homeowners start with the same question: do I actually need permission for this? The answer depends on your property type, what you are building, how big it is, and whether your home carries any extra protection.
Answer the questions below and BuildGuide will show you what to expect for each of the four consents that matter in England, plus the practical next steps to take. Nothing is saved and you do not need an account.
Use the tool
Your results
Answer the questions above and select “Check my extension” — your results will appear here.
Frequently asked questions
Does this tool give me planning permission?
No. It gives early guidance on what your project is likely to need. Only your local planning authority can grant permission or confirm that your project is lawful development.
What is the difference between planning permission and permitted development?
Permitted development is a national grant of permission for certain works, so no application is needed. Planning permission is a case-by-case decision made by your council when a project falls outside those limits.
Do I still need building regulations approval if I do not need planning permission?
Almost always yes. The two regimes are separate: planning controls what a building looks like and how it affects others, while building regulations control how safely it is built.
When does the Party Wall Act apply?
It applies when you work on a shared wall, build on or astride the boundary, or excavate within three or six metres of a neighbouring structure at a lower depth than its foundations. Notice must be served in advance.
Does a conservation area stop me extending?
No, but it removes some permitted development rights and means design, materials and the impact on the street scene will be assessed more closely.
Is my information saved?
No. Your answers stay in your browser for this session only. Nothing is stored and you do not need an account.
Ask Mason
Ask Mason about your extension
Get tailored, plain-English guidance for your home and situation — in under two minutes.
Recommended next steps
Read next
Planning Your House Extension
From first sketch to shovel-ready drawings, learn the practical steps that lead to a smooth, well-priced extension project.
Read guideDo I Need Planning Permission?
Find out whether your extension, loft conversion, outbuilding or home improvement needs planning permission. A clear UK guide for homeowners.
Read guidePermitted Development Rights Explained
Understand what Permitted Development Rights cover, the limits that apply and how to check whether your extension, loft conversion or outbuilding qualifies.
Read guideStructural Work and Party Wall Basics
A plain-English guide to structural work in the home and the Party Wall etc. Act 1996 for UK homeowners, covering when engineers are needed, what notices to serve and how to keep neighbours onside.
Read guideRecommended tools
Planning Permission Checker
Answer a few short questions about your home and your plans for an early, plain-English indication of whether planning permission is likely to be required.
Open tool Interactive toolAsk Mason: project checker
Describe your project and get tailored, plain-English guidance on the approvals, steps and risks that apply to your home.
Open tool Interactive toolBuilding Regulations Checker
Answer a few short questions about your home improvement for an early, plain-English indication of whether Building Regulations approval is likely to be required.
Open toolYou may also need
- Planning permissionCheck whether your local authority needs to approve the design before work starts.Planning Permission Explained
- Building regulationsStructural, fire, insulation and safety standards apply to most building work.Planning Permission vs Building Regulations
- Permitted developmentMany projects are allowed without a full application — within strict limits.Lawful Development Certificates Explained
- Party Wall ActWork on or near a shared wall usually needs notice served on your neighbours.Structural Work and Party Wall Basics
BuildGuide tools provide early guidance only. They are not a formal planning decision, legal opinion or professional design.