Reports needed for an annexe for a family member
The argument is about dependency, not room sizes. How officers judge an annexe against a separate dwelling, and what to submit so the answer goes your way.
The annexe planning reports a council asks for are modest. The argument is almost always about one thing: whether what you are building is part of your house or a second house. Get that framing right and a householder application with a planning statement and good drawings will usually do. Get it wrong and you are making a change of use application for a new dwelling in a back garden, against a different and much harder set of policies.
So write the application around the dependency, not around the room sizes.
Ancillary annexe against a separate dwelling
An ancillary annexe is accommodation that forms part of the planning unit of the main house. The occupant is part of the household in planning terms, even if they cook separately and have their own front door. A separate dwelling is its own planning unit, capable of independent occupation, and creating one in your garden is development that engages policies on garden land, density, amenity, parking and often on new dwellings in the countryside.
The distinction has nothing to do with who you intend to put in it. A council cannot grant permission on the basis of your mother living there and then treat the building differently when she no longer does, which is precisely why the condition discussed below exists.
Permitted development offers two partial routes. A single storey or two storey extension within the limits of Class A of Part 1 of the General Permitted Development Order 2015 can contain annexe accommodation, because it remains part of the dwellinghouse. A detached outbuilding under Class E must be incidental to the enjoyment of the dwellinghouse, and a building with a bedroom, kitchen and bathroom used as living accommodation is generally held not to be incidental. A lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful.
The tests an officer applies
There is no statutory checklist. Officers and inspectors look at the degree of physical and functional dependence, and the factors that recur are these:
| Factor | Points towards ancillary | Points towards separate dwelling |
|---|---|---|
| Access | Through or across the shared curtilage, no separate street access | Own gate, path and address from the highway |
| Curtilage | Garden shared and undivided | Fenced or walled to create its own plot |
| Facilities | Kitchenette rather than full kitchen, some facilities shared | Full kitchen, utility, own bin and cycle store |
| Services | Shared meters, shared boiler or heating circuit | Separate utility supplies and meters |
| Physical relationship | Attached, or close to the main house | Remote corner of the plot, screened from the house |
| Capability of separate sale | Would not function independently | Could be sold or let on its own |
| Scale | Clearly subordinate to the host dwelling | Comparable in size to the host dwelling |
No single factor decides it. A detached annexe can still be ancillary, and an attached one with a separate entrance can still be a separate dwelling. What persuades an officer is a design that is obviously dependent: a shared garden, a short covered link or a path from the back door, shared meters, and a kitchenette rather than a second family kitchen.
Scale deserves a word. A 65 square metre annexe beside a 90 square metre bungalow does not read as subordinate, whatever the drawings say about dependency. Keep it visibly smaller than the host dwelling.
Drainage and services, shared or separate
This is where applications accidentally make the case against themselves. Separate electricity and water meters, a separate gas supply, an independent boiler and a new drainage connection direct to the public sewer all read as evidence of a second dwelling.
Design the services as an extension of the house. One incoming water supply, one electricity supply with the annexe on a sub-circuit, heating from the existing system where the distance allows, and foul drainage connecting into the existing private drain rather than making its own connection.
Where the property is not on mains drainage, the position needs setting out properly. Additional population on a package treatment plant or septic tank may exceed its design capacity, and a Foul Sewage Assessment covering population equivalent, percolation results and the distance to any watercourse or borehole will be wanted. An existing system sized for a three bedroom house does not automatically absorb two more people.
Parking and access
Highway officers look at the whole site rather than the annexe alone. The question is whether the plot still provides parking to the council's standard for the total number of bedrooms and whether vehicles can enter and leave in forward gear where that is required.
Two things cause trouble. Converting a garage to form the annexe removes a parking space, and many councils count garages in their standards even though almost nobody parks in them. And a new or widened dropped kerb needs separate highway consent under section 184 of the Highways Act 1980, which is not granted by the planning permission.
Where the annexe is for a relative with limited mobility, say so in the planning statement and show the level approach, the door widths and the turning space. That material supports the dependency argument and addresses accessibility policy at the same time.
Conditions tying occupation to the main house
Expect a condition. The usual form restricts occupation of the annexe to persons related to or dependent upon the occupiers of the main dwelling, and provides that it shall not be occupied as a separate dwelling or disposed of separately from the host house. Some authorities also require the annexe to revert to ancillary use when no longer needed for a relative.
Three practical points about living with that condition:
- It binds successors in title, so it will appear in the buyer's searches when you sell, and it affects what a lender will accept.
- Breaching it is a breach of condition, which can be enforced at any time while the breach continues, and letting the annexe on the open market is the clearest possible breach.
- It can be varied later by an application under section 73, but the council will reassess the acceptability of a separate dwelling at that point and may refuse.
If your real intention is a separate dwelling, apply for one. An annexe permission with an occupancy condition used as a route to a second house is a well worn path and councils recognise it quickly.
Council tax and the levy
Two financial points worth settling before you build, because both have deadlines.
Community Infrastructure Levy: the levy regulations provide an exemption for a residential annex within the curtilage of the main dwelling, subject to conditions. It must be claimed and granted before development starts, and it is subject to clawback if the annex or the main dwelling is sold or let separately within the stated period after completion. Claim it in writing, keep the determination, and do not start work on the strength of an assumption.
Council tax: an annexe that is self-contained may be separately banded by the Valuation Office Agency, which is a different judgement from the planning one. Where it is occupied by a dependent relative, an exemption may apply, and where it is used as part of the main home by a family member a discount may be available. The rules sit with your council's council tax team and the Valuation Office, so ask them directly rather than assuming the planning position carries across.
The document set to submit
For most annexe applications the submission is short:
- Application forms and the correct fee for a householder application, or for a full application where the council treats the annexe as a new dwelling.
- Location plan, block plan, existing and proposed floor plans and elevations, and a site section where levels vary.
- A Planning Statement dealing with dependency head on: access, curtilage, services, facilities, scale and the family circumstances.
- A Design and Access Statement where the site is in a conservation area or the works affect a listed building.
- A foul drainage assessment where the site is not on mains drainage.
- A parking layout showing provision for the whole property against the council's standard.
- An arboricultural report where trees are affected, and our note on which reports a scheme with a Tree Preservation Order needs covers what that involves.
An illustrative example. A 1960s detached house with a 42 square metre single storey annexe attached by a glazed link, containing a bedroom, shower room and kitchenette, served off the existing boiler and meters, with the garden left undivided and parking for three cars retained. Permission granted with an occupancy condition. This example is illustrative.
Check your authority's validation checklist before submitting, since local requirements sit on top of the national list. And raise the dependency question at pre-application stage if there is any doubt, because it is far less costly to resolve in correspondence than at committee.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which reports your site is likely to need.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Can I build an annexe under permitted development?
Sometimes, where it forms part of the house. An extension within the limits of Class A of Part 1 can contain annexe accommodation because it remains part of the dwellinghouse. A detached outbuilding under Class E must be incidental to the enjoyment of the dwelling, and a building with bedroom, kitchen and bathroom used as living accommodation is generally held not to be incidental.
What makes an annexe a separate dwelling?
Capability of independent occupation, judged on physical and functional dependence. Officers look at whether there is a separate street access, whether the curtilage has been divided, whether facilities and services are shared, how far the building sits from the house, its scale relative to the host dwelling, and whether it could be sold or let on its own.
Will the permission restrict who can live there?
Usually yes. The standard condition limits occupation to persons related to or dependent upon the occupiers of the main dwelling and prevents separate occupation or disposal. It binds successors in title, so it appears in searches on sale and affects what lenders will accept. It can be varied under section 73, but the council will reassess the separate dwelling question.
Do I pay the Community Infrastructure Levy on an annexe?
An exemption is available for a residential annex within the curtilage of the main dwelling, subject to conditions in the levy regulations. It has to be claimed and granted before development starts, and it is clawed back if the annex or the main house is sold or let separately within the stated period after completion. Get the determination in writing first.
Should the annexe have its own meters and drainage connection?
No, if you want it treated as ancillary. Separate utility meters, an independent boiler and a new drainage connection direct to the public sewer all read as evidence of a second dwelling. Design the services as an extension of the house: one water supply, a sub-circuit for power, heating from the existing system, and drainage into the existing private drain.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.