Material Change of Use — What It Means and When You Need Planning Permission

Target keyword: material change of use planning permission UK Published by: RCB Design & Build | A2Z Principal Contractors Audience: Property owners considering converting between uses

If you are thinking about changing how a property is used — converting a house into a house in multiple occupation (HMO), splitting a house into flats, or converting a former commercial unit into residential — you may be moving into the territory of material change of use. Getting this wrong carries significant legal and commercial risk, including enforcement notices, difficulties on resale, and potential criminal liability in some circumstances.

This article explains what material change of use means in law, how the Use Classes Order works after 2020, and what routes are available to regularise or obtain permission for a change of use.

The Legal Definition

Under Section 55 of the Town and Country Planning Act 1990, any material change in the use of land or buildings constitutes development and requires planning permission — unless a specific exemption applies. Those exemptions come either from Permitted Development (PD) rights under the Town and Country Planning (General Permitted Development) (England) Order 2015, or from a specific prior approval route.

The word "material" matters. Minor or incidental changes are not development. The courts have historically considered whether the change would be noticeable to a reasonable observer of the use of the land over time.

The Use Classes Order 2020

The Town and Country Planning (Use Classes) (Amendment) (England) Regulations 2020 (SI 2020/757) made substantial changes to the use class system, effective from 1 September 2020. Understanding the current system is essential before making any conversion decision.

Class C3 (dwellinghouse) remains the category for single-family homes used by a single household. This has not changed.

Class C4 (small HMO) covers properties let to between three and six unrelated persons sharing facilities. In many areas, the change from C3 to C4 is Permitted Development under Class L of the GPDO 2015 — meaning no planning application is needed. However, many London boroughs have introduced Article 4 Directions removing this PD right. If you are in one of those boroughs, a full planning application is required for any C3-to-C4 change.

Sui generis uses include large HMOs (seven or more unrelated persons), care homes (Class C2), and live/work units. These always require a full planning application — there is no PD route.

Class E (commercial, business and service) is the major 2020 innovation. It merged the former A1 (retail), A2 (financial/professional services), A3 (restaurants and cafés), and B1 (offices, light industrial) into a single class. Changes between uses within Class E no longer require planning permission, providing greater flexibility for commercial landlords.

The Prior Approval Route for Commercial-to-Residential

Class MA of the GPDO 2015 (introduced in August 2021) allows buildings in Class E use to be converted to Class C3 residential through a prior approval process rather than a full planning application. This is a significant permitted development right, but it comes with conditions. The building must have been in commercial use continuously for at least two years before the application date and must have been in commercial use on 1 March 2021. The gross floor area of the building must not exceed 1,500 square metres, and a prior approval application must be submitted to the local planning authority, which has 56 days to determine it. For buildings over 18 metres in height, a fire safety report is required following the Building Safety Act 2022.

When Full Planning Permission Is Required

A full application is needed wherever no PD right or prior approval route applies. Common examples include: any change from Class C3 to Class C2 (such as a care home); any commercial conversion exceeding the Class MA floor area limit; change of use to a sui generis category; and conversion of a house into two or more self-contained flats.

It is worth noting that converting a house into flats is not simply a change of use — it is also a development involving physical operations and must comply with Building Regulations Parts B, E, F, G, and the drainage requirements of Part H. The planning permission and building regulations approval are separate processes.

Lawful Development Certificates

Where you are relying on a permitted development right for a change of use, you do not technically need to apply for permission — but you are strongly advised to obtain a Lawful Development Certificate (LDC) under Section 192 of the TCPA 1990 from the local planning authority. This formal confirmation that the change is lawful is important for mortgage lenders, future buyers, and conveyancers. Without it, your solicitor will face difficulties on any resale.

Practical Scenarios for London Homeowners

If you rent a room in your home while you live there, this does not constitute a change of use to an HMO. If you let your house to four students, you may have a C4 HMO — check whether an Article 4 Direction applies in your borough. If you want to convert your house into two flats, you need planning permission. If you want to convert a ground-floor office into a flat, the Class MA prior approval route may be available.

RCB Design & Build confirms the planning position — including the applicable use class, any Article 4 restrictions, and the correct application route — before advising on or commencing any conversion project.