Modular Extension Planning Checker

A modular or offsite extension follows the same planning rules as any other extension: the factory build does not change what you are allowed to put on the ground. Answer the questions below and this checker gives you a likely outcome, the specific rule behind it, and what to do next. Key insight: most single-storey rear extensions fall under permitted development, but a few measurements (depth, eaves height near a boundary, distance to the rear boundary on two storeys) decide it.

This checker covers householder permitted development in England under the General Permitted Development Order (Class A). Scotland, Wales and Northern Ireland have their own rules. Flats and maisonettes have no householder permitted development rights, and homes where rights have been removed by an Article 4 direction or a planning condition are treated as needing an application. It is a guide, not a decision: always confirm with your local planning authority or a lawful development certificate before you build.