150 sqm Class R Rule: The Conversion Councils Can't Refuse
The 150 sqm Class R Rule: Why Your Council Can't Refuse Your Agricultural Conversion
If you own an agricultural building in England and you want to turn it into a commercial space, there is a rule in the planning system that sits quietly in the background — and most farmers and landowners have never heard of it.
It is the 150 square metre threshold in Class R of the General Permitted Development Order. And used correctly, it removes the local planning authority's ability to refuse your change of use.
Not "makes it harder to refuse". Removes it. Below 150 sqm under Class R, the council has no prior approval power. Your only obligation is to tell them you are doing it.
This article explains how the 150 sqm Class R rule works after the May 2024 reforms, which buildings qualify, the small print that catches people out, and how to use it to convert a redundant agricultural building into commercial use without going through a full planning application — or even a prior approval determination.
What Class R Actually Is
Class R is part of Schedule 2, Part 3 of the Town and Country Planning (General Permitted Development) (England) Order 2015. It is the permitted development right that allows agricultural buildings to change use to what the legislation calls a "flexible commercial use".
In practical terms, that includes Class E (commercial, business and service uses — shops, offices, gyms, cafes, light industrial, indoor sport, medical services), Class B2 (general industrial), Class B8 (storage and distribution) and Class C1 (hotels). One agricultural building, lawfully converted, can become a farm shop, an office, a microbrewery taproom, a wedding storage business, a small hotel, or a workshop unit — without ever submitting a planning application.
The 2024 reforms, which came into force on 21 May 2024, made Class R substantially more powerful. The cumulative floor space cap on an agricultural unit was doubled from 500 sqm to 1,000 sqm. The list of qualifying uses was widened. And — most importantly for the purposes of this article — a clear two-tier procedural distinction was introduced based on floor space.
The 150 sqm Threshold: The Rule That Changes Everything
Under the amended Class R, any change of use of 150 sqm or less is subject to notification only. There is no prior approval procedure. There are no matters the council is permitted to assess. There is no determination to refuse.
The developer must notify the local planning authority of the date the new use will begin. That is the full extent of the engagement.
Above 150 sqm, prior approval is required, and the council can assess matters such as transport and highways impact, noise, contamination, flooding risk, the suitability of the location for the proposed use, and design or external appearance where works are involved. They can refuse on those grounds.
Below 150 sqm, none of those matters are in scope. The council has no statutory mechanism to refuse a Class R change of use of 150 sqm or less, provided the eligibility conditions are met.
This is the rule. And almost nobody is using it.
Why the Council Can't Refuse
The reason the council cannot refuse is structural. Permitted development rights granted by the GPDO are a form of planning permission granted by Parliament, not by the local authority. When the legislation says no prior approval is required, the council has no decision-making power to exercise.
A notification under Class R is not an application. It is not assessed. It is not consulted on. The council records it and the change of use proceeds.
The only way the council can intervene is by issuing an Article 4 Direction removing Class R rights in a defined area before the change of use occurs. Article 4 Directions are not common, they require ministerial oversight, and they cannot be applied retrospectively to a notification that has already been served.
In any area where Class R rights have not been withdrawn by an Article 4 Direction, a compliant notification below 150 sqm cannot be refused.
What Counts as 150 sqm
The 150 sqm threshold refers to the total floor space changing use to a flexible commercial use. It is measured as the internal floor space of the building, including all floors where the change of use applies.
The threshold is cumulative across the agricultural unit. If a previous Class R change of use of 80 sqm has already taken place on the holding, only 70 sqm of further Class R conversion is available under the notification-only tier before the threshold is crossed and prior approval becomes necessary.
The wider 1,000 sqm cumulative cap on the unit still applies above the 150 sqm threshold. So an agricultural unit could, in principle, deliver 150 sqm under notification and a further 850 sqm under prior approval — provided each stage meets the conditions.
Which Buildings Qualify
For a building to qualify for Class R, several conditions must be met. These conditions catch the unwary, and they are the only basis on which a notification can fail.
The building must be an agricultural building situated on an agricultural unit. It must have been used solely for an agricultural use as part of an established agricultural unit on either 3 July 2012, or — if it came into agricultural use after that date — for at least ten years before the change of use takes place.
The building must not be a listed building. It must not be on the site of a scheduled monument. It must not be within an area of safety hazard or a military explosives storage area. Sites of Special Scientific Interest are subject to additional restriction.
The building does not need to be structurally sound in the way that Class Q residential conversions require. Class R is more flexible on this point because the building is being repurposed for commercial use, not residential occupation. But the building must already exist — Class R does not permit new build.
If any of these conditions is not met, Class R does not apply. A notification will not retrospectively cure ineligibility. The local authority is entitled to investigate compliance with the conditions, and if the conditions are not met, the change of use is unauthorised development and enforcement may follow.
This is where the value of professional planning advice comes in. A notification that does not engage with eligibility is exposed. A notification supported by a properly prepared evidence base — agricultural use history, building condition, status checks against designations — is robust.
What You Can Do With 150 sqm
150 sqm is a meaningful footprint. To put it in context:
A typical agricultural building of around 12 metres by 12 metres falls comfortably within the threshold. A modest steel-frame portal building converts neatly into a commercial workshop, a farm shop, a small office suite, a brewery taproom, or a holiday let reception and ancillary space within this footprint.
For diversification purposes, 150 sqm under notification is a sensible starting point. It establishes the lawful commercial use, generates income, and demonstrates the viability of the site without the cost, time, and risk of a prior approval submission or a full planning application.
It is also possible to take 150 sqm under notification first, operate the use, and then bring forward a separate prior approval application for further floor space later. The Class R route is incremental.
The Mistakes That Lose People the Right
The most common reason a Class R conversion fails is not council refusal. It is non-compliance with the eligibility conditions, which the developer either did not check or assumed away.
The building was not in solely agricultural use on 3 July 2012, because it had been used incidentally for storage of non-agricultural items, or because a small office in the corner had been let to a third party. The building was constructed in 2017 and the ten-year rule is not yet satisfied. The agricultural unit was broken up several years ago and the building is no longer on an agricultural unit. The building is listed, or within the curtilage of a listed building, and curtilage listing was not picked up.
Any of these breaks Class R. The notification has no protective effect because the right does not apply.
The second common failure point is the notification itself. The notification must be served correctly, contain the right information, and identify the building and the use with sufficient particularity. A casually drafted notification that does not engage with the requirements of the Order can be challenged.
The third issue is enforcement risk where the council disputes eligibility. A well-prepared file — historical aerial photography, agricultural unit confirmation, building age and use evidence, designation checks — is the best protection against that risk.
Building Works Under Class R
Class R primarily authorises the change of use. It does not give wide latitude for external building works. Limited building operations reasonably necessary to convert the building to the new use are permitted, but substantial rebuilding, extension, or alteration of the external appearance can fall outside what Class R permits.
Where external works are needed, a separate planning consideration may apply. Below 150 sqm and within a notification-only context, this is an area to take advice on before starting work.
How Class R Compares to Class Q
Class Q is the residential equivalent — agricultural to dwellinghouse. Class R is the commercial counterpart. They are often confused.
Class Q is more restrictive. It carries strict structural requirements, contributions to housing supply considerations, and a more demanding prior approval regime. Class R has lower hurdles because the use is commercial, not residential.
For landowners considering options for a redundant building, Class R is often the faster and lower-risk route to bringing the building back into productive use, particularly where residential conversion would be difficult or where a commercial diversification is more aligned with the holding's business strategy.
Using the 150 sqm Rule Strategically
The 150 sqm Class R rule rewards planning. The landowners who get the most out of it are those who think about the sequence:
Identify the right building first. Confirm eligibility against all the Class R conditions before committing to fit-out costs. Establish the commercial use that fits the site, the local market, and the wider business. Serve the notification. Begin the use. Build the trading history. And then, if appropriate, expand under prior approval up to the 1,000 sqm unit cap.
Done well, this is a route to commercial diversification income that bypasses the conventional planning system entirely. Done badly, it is enforcement exposure.
The Bottom Line
The 150 sqm Class R rule is the most underused planning right available to English farmers and rural landowners. It allows a change of use to a wide range of commercial uses without prior approval, on a notification basis, in any agricultural building that meets the eligibility conditions.
The local planning authority cannot refuse a compliant notification. They have no statutory mechanism to do so. The only ways for the conversion to fail are failure to meet the eligibility conditions, an existing Article 4 Direction, or a defective notification.
For any landowner with a redundant or underused agricultural building, the question is not whether Class R is worth considering. It is whether the building qualifies, and whether a notification or a prior approval is the right route for the proposed use.
If you would like Foxes Rural to assess a building for Class R eligibility, prepare the notification, and put the evidence base in place to protect the conversion against challenge, we handle that work routinely. Get in touch.