When nine houses and an annexe becomes ten dwellings

A scheme of nine houses with a granny flat over the garage of plot one is either a nine unit application or a ten unit application, and the difference decides whether it is major development. Whether an annexe is counted as a dwelling turns on one question: does the annexe form a separate planning unit, or is it accommodation ancillary to the house it sits with. Floor area, the word on the drawing and the council tax band do not settle it.

Get this wrong in the applicant's favour and the authority re-registers the application as a major, re-advertises it, and the eight week determination becomes thirteen. Get it wrong the other way and you have paid for an affordable housing position you did not need.

The test for a separate planning unit

The framework comes from Burdle v Secretary of State for the Environment, decided in 1972, and it still governs. Start with the unit of occupation. Where the whole of that unit is used for one main purpose and other activities are ancillary to it, the whole is a single planning unit. Where within a single unit of occupation there are two or more physically separate and distinct areas occupied for substantially different and unrelated purposes, each area is a separate planning unit.

Applied to an annexe, the question becomes whether the occupants of the annexe live as part of the household in the main house or as a separate household. Living as part of the household means sharing something real: the garden, the front door, the kitchen, the laundry, the bins, the car. Living separately means a unit that functions on its own and would be let or sold on its own without alteration.

Creating a separate dwelling is a material change of use and therefore development under section 55 of the Town and Country Planning Act 1990. That is why the point matters beyond arithmetic: an annexe that becomes independent without permission is a breach of planning control as well as an extra unit.

Facilities, access and shared use

Officers work through a familiar list, and so should you before you submit.

No single feature decides it. A detached annexe with its own kitchen at the bottom of a long garden, with a gate onto a side road, is a separate dwelling in all but name. The same building attached to the house, with an internal door and a shared drive and garden, is not.

Degree of separation is a matter of planning judgement, which means an officer can take a different view from yours. Where the answer matters to the unit count, raise it at pre-application and get the view in writing.

What changes at the tenth dwelling

Article 2 of the Development Management Procedure Order 2015 defines major development for residential schemes as the provision of ten or more dwellings, or development on a site of half a hectare or more where the number of dwellings is not known. Note the second limb carefully: nine dwellings on a one hectare site is not major, because you know the number.

Crossing into major territory changes several things at once:

• Publicity moves to a site notice and a newspaper advertisement
• The determination period becomes thirteen weeks rather than eight
• The national affordable housing threshold is engaged, so an Affordable Housing Statement becomes part of the pack
• The application fee band changes
• Biodiversity net gain moves from the small sites approach to the full statutory metric
• Contributions towards education, open space and child yield and play space are more likely to be sought
• Waste storage and collection standards are applied more strictly
• In many authorities the application moves from delegated powers to committee, which is covered in our note on the shift from a delegated decision to committee

The cost consequences are not evenly spread. The affordable housing requirement is usually the largest, and on a nine unit scheme the step up to ten can wipe out the margin on the tenth home and some of the ninth.

Conditions that tie an annexe to the host dwelling

Where the annexe is accepted as ancillary, the authority will almost always impose a condition. The standard form restricts the use of the annexe to purposes incidental or ancillary to the enjoyment of the main dwelling and prohibits its occupation as a separate dwelling.

Some authorities go further and tie occupation to a dependent relative or a family member. Those conditions are harder to justify, because guidance on the use of conditions treats restrictions tied to a particular person as rarely appropriate, and they create problems when the relative dies or moves. If one is proposed, ask for the ancillary use wording instead and offer to accept a restriction on subdivision of the curtilage.

A condition of this sort is enforceable for as long as it stands on the permission. Selling the annexe separately, letting it on an assured tenancy or advertising it as a holiday let are all breaches, and all three are visible from the street or from a listing site.

Council tax banding is a different question

A self-contained annexe is commonly given its own council tax band by the Valuation Office Agency, with a discount where it is occupied by a relative or used by the occupier of the main dwelling. That assessment is made under council tax legislation for revenue purposes, and it says nothing authoritative about planning status.

The two regimes pull apart. An annexe can be separately banded and still be ancillary in planning terms, and a planning condition restricting occupation does not stop the valuation officer banding it. Expect the point to be raised, in both directions: by a neighbour objecting that a tenth dwelling is being created, and by an enforcement officer who has pulled the banding record. The answer is the planning unit test, supported by how the building is actually used.

Drawing the annexe so the point does not arise

If the intention is ancillary accommodation, draw it that way from the start.

1. Connect it internally to the host dwelling, or share the entrance hall.
2. Keep the garden as one space, with no fence, hedge or gate dividing it.
3. Show shared parking rather than an allocated bay.
4. Specify a kitchenette rather than a full kitchen, and label it on the plan.
5. Keep services on the host dwelling's supplies.
6. Show the annexe within the curtilage and close to the house rather than at the boundary.
7. Name the rooms on the drawing as part of the host dwelling.

And describe it accurately in the application description. A proposal described as a one bedroom dwelling will be counted as one, whatever the supporting statement says later.

Rectifying a scheme that has tipped over

Four options, in rough order of cost.

Redesign the annexe to be clearly ancillary, and accept a condition. This usually means losing the separate entrance and the private garden.

Accept major status and build the scheme at ten units, with the affordable housing position resolved. On some sites the tenth unit pays for itself.

Reduce the scheme to eight houses plus the annexe, if the arithmetic works better with a smaller affordable requirement and a shorter determination.

Or seek an amendment to an existing permission. A non-material amendment under section 96A cannot change the number of dwellings, so the route is usually an application under section 73 to vary the relevant condition or a fresh application, depending on what the permission says.

One honest caveat: the line between an ancillary annexe and a separate dwelling is a judgement rather than a rule, and inspectors have reached different conclusions on broadly similar buildings. The further you keep the annexe from the line, the less of your programme is spent arguing about it.

Enter your postcode on PlanScope to see which reports a nine or ten unit scheme on your site is likely to need.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.