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Project CalculatorBuild it on screen and see the moment you cross a line in the rules.Street CheckWhat your neighbours got approved, and what that means for you.Feasibility sketchSend a photo of your house, get a concept drawn over it.Cost calculatorHonest price ranges by project type and region.

Most used Try the Project CalculatorDrag a slider and watch the drawing turn amber the moment you leave permitted development. No email needed. Open the Project Calculator →

Find your councilApproval rates and local rules, council by council.London boroughsAll 33, with Article 4 coverage.Article 4 directionsWhere permitted development is switched off.How long it takesThe eight weeks, and the truth.

Most used Try the Project CalculatorDrag a slider and watch the drawing turn amber the moment you leave permitted development. No email needed. Open the Project Calculator →

Permitted developmentWhat you can build without asking.Refused? What nextAppeal or resubmit, and how long each takes.Party wall agreementsWhen you need one and what it costs.Building regs vs planningTwo approvals, two risks.All guidesThe full library.

Most used Try the Project CalculatorDrag a slider and watch the drawing turn amber the moment you leave permitted development. No email needed. Open the Project Calculator →

Rear extensionThe most common project in the UK.Loft conversionThe cheapest bedroom you can add.Side returnThe alley beside a terrace, brought inside.Two storeyBetter value per square metre.WraparoundSide and rear combined.All project costsEvery type, side by side.

Most used Try the Project CalculatorDrag a slider and watch the drawing turn amber the moment you leave permitted development. No email needed. Open the Project Calculator →

Guide

Building regulations and planning permission are not the same thing

Two separate approvals, two separate risks. What each one covers and why passing one does not help with the other.

The same extension drawn twice, once as an outer shell and once cut open to show structure and services — Planning judges the outside, building control judges the inside

Two approvals, two entirely different questions

Planning asks whether the thing should exist. Building regulations ask whether it is safe. Passing one tells you nothing about the other, and this catches people constantly.

Planning permission

Concerned with appearance, scale, overlooking, light, and impact on the street and neighbours. Decided by the local planning authority. Can be avoided entirely if your project is permitted development.

Building regulations

Concerned with structure, fire escape, insulation, ventilation, drainage and safe access. Signed off by building control, either the council or an approved inspector. Cannot be avoided. Every extension and loft conversion needs it, including permitted development ones.

Why this matters when you sell

A buyer's solicitor will ask for a completion certificate. Work without one is a problem at sale, and indemnity insurance is a patch rather than a fix. The certificate is the thing that proves the work was done properly.

Project Calculator

Does this apply to your house?

Reading the rules is one thing. The Project Calculator applies them to your house and shows you the answer as a drawing, with the cost alongside.

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More guides

Diagram of a house inside a dashed envelope showing the limits permitted development allows

Permitted development rights, explained properly

What you can build without planning permission, what the limits actually are, and the traps that catch people out.

Four houses in a row showing a project progressing from bare house to completed extension

How long does planning permission actually take?

The statutory eight weeks, what really happens, and where the time goes on a householder application.

Two versions of the same house, one refused scheme in red and one revised scheme approved in green

Your planning application was refused. What now?

Why householder applications get refused, whether to appeal or resubmit, and how long each route takes.

A terrace of houses with a dashed boundary running through it, one half inside a designated zone

Article 4 directions, and why they matter to you

How councils remove permitted development rights, how to find out if yours is affected, and what it changes.

Two adjoining houses with the shared party wall highlighted and notice zones marked on the ground

Party wall agreements without the jargon

When you need one, what it costs, how long it takes, and what happens if your neighbour objects.

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Twenty minutes with the team that sweats the details.

No obligation, no script. An honest read on what your house can do, from people who obsess over getting it approved.

Twenty minutes, by phone or video, whenever suits
Anywhere in the UK, whatever your council
You leave knowing what is possible, and roughly what it costs

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