Class M: Extension and Alterations to Public and Institutional Buildings

Introduction

Class M is a permitted development right in England under the Town and Country Planning (General Permitted Development) (England) Order 2015. It allows certain public and institutional buildings, such as schools, colleges, universities, hospitals, and prisons, to carry out extensions, alterations, or minor works without needing a full planning application. This simplifies the process for institutions to improve facilities, while still ensuring that sensitive areas and heritage sites are protected.

What is Class M Planning?

Class M provides planning flexibility specifically for:

• Educational institutions (schools, further education colleges, universities)

• Hospitals and healthcare facilities

• Prisons and other correctional facilities

Under Class M, permitted development may include:

• Horizontal or vertical extensions of existing buildings

• Alterations to buildings to improve functionality

• Construction of ancillary structures (e.g., storage, plant rooms)

• Minor works on the curtilage, such as hard surfaces or service areas

It does not allow for change of use or works exceeding strict limits, and some projects may still require prior approval from the local planning authority.

Size & Percentage Limits (Key Restrictions)

Under Class M, development is not permitted if the following limits are exceeded:

(a) Cumulative footprint/ floorspace limit

The total amount of new building work (including both new buildings and extensions/alterations under Class M on or after 21 April 2021) must not exceed:

• 25% of the cumulative footprint of the relevant existing buildings as it was on 21 April 2021, or

• 250 square metres,

whichever is the greater.

(b) Boundary proximity limit

• For college, university, prison or hospital buildings:
  No part of the development may be located within 5 metres of the boundary of the curtilage.

• For schools specifically:
  If adjacent land is used for residential purposes, no part of the development may be within 5 metres of the boundary with that land.

(c) Height limits

• Any new building erected must not exceed 5 metres in height.

• If extension or alteration is within 10 metres of a boundary, the resulting height must also not exceed 5 metres.

(d) Playing field restriction

Class M cannot be used if the development would mean that land which has been used as a playing field in the last 5 years could no longer be used for that purpose.

Recent Updates to Class M Legislation

The government periodically updates permitted development rights. Key recent changes include:

• Clarified limits on height and site coverage for institutional extensions

• Expanded flexibility for operational works in hospitals and schools

• Increased focus on environmental and heritage safeguards, ensuring works do not impact protected areas

• Introduction of stricter prior approval triggers, especially for flood risk, highways, or conservation issues

These updates aim to balance institutional needs with community and environmental protection.

Eligibility Criteria for Class M

A building or site is generally eligible for Class M if it meets the following:

1. Institution type - Schools, colleges, universities, hospitals, prisons, or other state institutions

2. Existing use - The building must already be used for the relevant institutional purpose

3. Scale of works - Extensions or alterations must stay within prescribed size, height, and footprint limits

4. Operational purpose - Works must support the institution’s function and not constitute a change of use

5. Prior approval compliance - Where required, approval must be obtained for highways, flood risk, or heritage impact

Buildings and Sites Excluded from Class M

Class M rights cannot be used on the following:

• Listed buildings or structures within scheduled monuments

• Sites in National Parks, Areas of Outstanding Natural Beauty (AONB), or World Heritage Sites

• Areas within a Conservation Area (for certain types of works)

• Works exceeding height or footprint limits

• Development that affects playing fields, sports areas, or protected trees

• Projects needing separate consents, such as environmental permits or heritage consents

Local authorities may also restrict Class M rights using Article 4 Directions, removing permitted development rights in sensitive areas.

Why Class M Matters

Class M is important because it:

• Speeds up delivery of essential facilities in schools, hospitals, and prisons

• Reduces bureaucracy and cost for public institutions

• Supports modernization and expansion without full planning applications

• Balances development with environmental and heritage protection

• Encourages efficient use of public buildings while safeguarding community interests

In short, Class M provides a streamlined, regulated pathway for improving public and institutional buildings while maintaining planning oversight where it matters.