Changing the use of part of a building only

A change of use part of building application is possible, and whether it works depends on whether that part is a separate planning unit. Section 55 of the Town and Country Planning Act 1990 defines development to include a material change in the use of any building, and the courts read that against the planning unit rather than against the bricks. Where part of a building is physically separate and distinct and used for a substantially different and unrelated purpose, it can be its own planning unit. Where it is not, changing it changes the character of the whole.

Answer that question first. The application form, the red line, the conditions and the evidence all follow from it.

Whether part of a building can have its own use

The framework comes from Burdle v Secretary of State for the Environment, which set out three situations.

Where the whole building is used for a single main purpose with subsidiary activities incidental to it, the whole is one planning unit. A shop with a stock room above is one unit, and the stock room has no separate use of its own.

Where two or more activities occur without either being incidental to the other, and the occupier's activities are not confined to separate physically distinct areas, the whole is still one unit.

Where within a single unit of occupation there are physically separate and distinct areas occupied for substantially different and unrelated purposes, each area can be a separate planning unit.

The starting point in each case is the unit of occupation. So the first question is not architectural, it is about who occupies what, under what arrangement, and whether the activities are related.

One statutory exception is worth flagging. Section 55(3)(a) provides that using a building previously used as a single dwellinghouse as two or more separate dwellinghouses involves a material change of use of the building and of each part of it. Subdividing a house is always development, whatever the physical arrangements.

Physical separation and independent access

Where you are arguing that part of a building has its own use, these are the indicators that carry weight, in rough order of importance:

1. Independent access from the street or a common area, without passing through the other use.
2. Physical separation, with a solid wall or a locked door and no functional internal connection.
3. Separate occupation, under a distinct lease, tenancy or licence, to a different occupier.
4. Separate services and metering for water, electricity, gas and drainage.
5. A separate entry in the rating list or council tax valuation list.
6. A separate postal address and letterbox.

A part with all six is very likely a separate planning unit. A part with only the first two, still occupied by the same business, probably is not.

The point most often misjudged is access. A first floor reached only through the ground floor shop is functionally part of that shop, whatever the drawing says. Creating an independent entrance is frequently the single change that makes a partial change of use arguable, and it is also development in its own right where it alters the external appearance.

Describing a partial change on the application form

Precision in the description saves an enforcement argument later. Identify the part by floor and by reference to a plan, and name both the existing and proposed classes.

Something in this form works: change of use of the first and second floors from Class E(g)(i) office to three flats within Class C3, with alterations to form a new entrance at ground floor. Then attach existing and proposed plans with the affected part hatched and a key.

Draw the red line around everything the proposal needs, which usually means more than the part itself. If the flats use a shared stair, a bin store in the yard and cycle parking under the arch, all three go inside the red line. Land in the applicant's control that sits outside the red line goes in a blue line.

A red line drawn tightly around the changing floors alone, with no access, no bin store and no cycle parking, is the commonest reason these applications fail validation.

Shared services, stairs and circulation

Shared circulation is where partial change of use schemes get difficult, and the difficulty is both legal and practical.

Legally, a shared stair weakens the argument that the part is physically separate and distinct, because the two uses depend on the same route. Practically, it raises fire separation, access control and management questions that a case officer and a building control body will both ask about.

Workable arrangements share three features. A protected route with proper separation between the uses, so that a fire in the commercial unit does not compromise escape from the residential part. Access control that lets residents in without letting commercial customers upstairs. And a written arrangement about cleaning, lighting and maintenance of the shared area, which matters more once the parts are in different ownership.

Where services are shared, the practical question is what happens when one part is sold. Shared drainage, a single water supply and a shared boiler all need to be dealt with in the legal documents, and unresolved arrangements make the residential part difficult to mortgage.

Where the whole unit is treated as changing

Sometimes a change to part of a building is a material change of use of the whole, and this is where applicants get caught.

It happens in three situations. Where the part being changed was ancillary to the main use, so removing it changes what the main use is. Where the new use in the part alters the character of the whole planning unit, for instance turning a storage area into a hot food takeaway serving the street, which our note on hot food takeaway as a sui generis use covers. And where the parts remain functionally interdependent, so that neither can operate without the other.

The prior approval route from commercial premises to residential under Class MA does apply to part of a building, subject to its own conditions on prior vacancy, the period of qualifying use and a floorspace limit, as set out in our note on Class MA prior approval. Read the conditions against the part you are changing rather than against the whole building, because the floor area that counts is the part being converted.

Movement between the limbs of Class E is not development at all, so a partial change within Class E often needs nothing, as our note on change of use within Class E explains. That is the quickest answer available, and it is worth testing before assuming an application is needed.

Conditions tying the parts together

Expect the council to want the relationship between the parts controlled, particularly where the commercial floorspace is being protected by policy.

Conditions in common use include a requirement that the commercial unit be retained in its class, a restriction preventing the residential part from being occupied until the commercial unit is fitted out or let, a limit on the hours of the commercial use to protect the new residents, and a condition requiring the shared circulation to be maintained as approved.

More onerous is a restriction on separate disposal of the parts, usually imposed through a section 106 obligation rather than a condition. Read that drafting carefully before you accept it, because it affects value and lending on both parts.

The hours condition deserves particular attention. Introducing residential use above a commercial unit gives the council a reason to restrict the hours of a business that previously operated without complaint, and a landlord may find a sitting tenant's operation constrained by their own residential scheme.

Rating and council tax as separate consequences

Changing the use of part of a building has valuation consequences that follow automatically and are not part of the planning decision.

A part that becomes residential moves from non-domestic rating to council tax banding, and a building with both may be assessed as a composite property. The Valuation Office Agency reaches its own view on the basis of what is physically there and how it is occupied, and that view can be reached on a different timetable from the planning decision.

None of this determines the planning unit. But the rating and council tax entries are useful evidence of separate occupation, and an applicant arguing that a part is separate while both parts sit in a single rating assessment is arguing against their own paperwork.

Evidence on the extent of the change

Put the following in front of the case officer and the assessment becomes straightforward.

Existing and proposed floor plans for every level, with the use of each area annotated and floor areas scheduled by class. A schedule totalling the floor area changing and the floor area unaffected. Photographs of the internal connections, the access arrangements and the shared circulation. Copies of the leases or tenancy arrangements for each part. The rating list and council tax entries. A plan showing meter positions and service routes.

Then set out in the Planning Statement how the parts function, why the changing part is or is not a separate planning unit, and what happens to the remainder. Where trip generation or servicing changes materially, a Transport Statement covers that ground.

Where the answer carries real money, a certificate of lawfulness of existing or proposed use under sections 191 or 192 of the 1990 Act gives you a formal determination rather than a view.

This is general guidance rather than legal advice. Planning unit questions turn on the facts of the individual building and its occupation, so check the position with your local planning authority or a qualified professional before relying on it.

Working out which documents a partial change of use needs? Enter your postcode on PlanScope to see the likely list. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.