Planning Law

Annexe Planning UK, Permission and Permitted Development

An annexe is a secondary residential unit ancillary to the main dwelling; typically a converted garage, outbuilding, or purpose-built addition. The key planning question is whether the annexe is an ancillary use within the main C3 dwelling (likely permitted development or householder planning permission for works; no separate permission for the use) or a separate C3 dwelling unit (requires full planning permission for a new dwelling). Permitted development rights (GPDO 2015 Schedule 2, Part 1): cover the physical works (outbuilding construction; garage conversion to habitable room within size/height limits) but do NOT authorise the creation of a new separate self-contained dwelling; s.100ZA TCPA 1990 and GPDO Part 1 PD rights are about works, not use as a new dwelling; using a converted outbuilding as a self-contained letting (own kitchen, bathroom, entrance, meter) without full planning permission for a new dwelling is a breach of planning control. Ancillary vs separate dwelling (planning fact and degree): indicators of separate dwelling: self-contained facilities (own kitchen, bathroom, sleeping, separate entrance); can be occupied independently; let to a stranger on the open market; no functional relationship to main household; Gravesham BC v SOSE [1984]. Indicators of ancillary: connecting internal door to main house; occupied by a dependent relative who is part of the main household; no separate meter. Council tax: self-contained annexe = separate VOA banding = separate council tax bill; dependent relative discount (LGFA 1992 s.11A): 50% discount where the annexe is the sole or main residence of a person aged 65+, severely mentally impaired, or substantially permanently disabled; ancillary annexe with no separate kitchen = typically included in main dwelling assessment. Holiday let: 210+ days available + 140+ days actually let = business rates (not council tax); small business rates relief may eliminate liability. CGT: annexe used as part of main dwelling = PRR applies; annexe let to third party = no PRR for that portion; apportionment of gain required where use changed. SDLT: multiple dwellings relief (MDR) may be available if the annexe constitutes a genuine separate dwelling on purchase; HMRC scrutinises carefully. Income tax: rent-a-room scheme (£7,500 p.a.) applies only to furnished accommodation within the same building as the landlord's main residence, NOT a separate outbuilding annexe; full rental income from outbuilding annexe is taxable. Scotland: separate PD regime under Town and Country Planning (General Permitted Development) (Scotland) Order 1992, as amended.

11 min readUpdated 7 June 2026Last reviewed: 7 June 2026 by Richard Wood, Founderannexe-planning-permissionannexe-council-taxannexe-permitted-developmentannexe-separate-dwelling

Written and reviewed byRichard Wood· Founder, LetSafe UKLast reviewed: 7 June 2026

Planning Status of Annexes, Permitted Development and Separate Dwelling

Permitted development rights (GPDO 2015 Schedule 2, Part 1, householder development): cover the physical works for outbuilding construction and garage/outbuilding conversion within size and height limits; do NOT authorise the creation of a new self-contained separate dwelling; using a converted outbuilding as a self-contained letting (own kitchen, bathroom, separate entrance, meter) without full planning permission for a new dwelling = breach of planning control; s.100ZA TCPA 1990 restricts LPAs to imposing pre-commencement conditions only with applicant agreement or where necessary. Ancillary vs separate dwelling (planning fact and degree): separate dwelling indicators; self-contained facilities (own kitchen, bathroom, sleeping, separate entrance); can be occupied independently; let to a stranger on the open market; no functional relationship to the main household; Gravesham BC v SOSE [1984]; ancillary indicators, connecting internal door to main house; occupied by a dependent relative who is part of the main household; no separate utility meter; same council tax and address as main dwelling. Article 4 direction: in many areas, Article 4 directions remove PD rights, check with the LPA before relying on PD rights for annexe works. Scotland: the Town and Country Planning (General Permitted Development) (Scotland) Order 1992 (as amended), similar principles but different categories and size limits. Wales: Welsh PD regime differs from England in some respects.

Council Tax, CGT, SDLT, and Income Tax Implications

Council tax: self-contained annexe (own kitchen, bathroom, entrance) = separate VOA council tax band = separate bill in addition to main dwelling; dependent relative discount (LGFA 1992 s.11A): 50% discount where the annexe is the sole or main residence of a person aged 65+, severely mentally impaired, or substantially permanently disabled; ancillary annexe with no separate kitchen = typically included in main dwelling's council tax assessment; holiday let available 210+ days + actually let 140+ days = business rates (not council tax), small business rates relief may eliminate liability; empty annexe premium: many councils charge 25%£100% council tax premium on long-term empty domestic properties. CGT and private residence relief: annexe used as part of main dwelling = PRR applies on same basis as main house; annexe let to third party = no PRR for that portion; apportionment of gain required where use changed over the ownership period. SDLT multiple dwellings relief (MDR): may be available if the annexe constitutes a genuine separate dwelling on purchase; HMRC scrutinises MDR claims carefully, the annexe must be self-contained and functionally independent; the government reversed a proposed abolition of MDR for annexe purchases in 2024. Income tax: rent-a-room scheme (£7,500 p.a. exemption for furnished accommodation) applies only to accommodation within the same building as the landlord's principal residence, NOT to a separate outbuilding annexe; full rental income from an outbuilding annexe is taxable (subject to allowable expenses and the £1,000 property income allowance). Planning and tax: planning status and tax treatment are assessed independently, the VOA and HMRC make their own determinations regardless of the LPA's view.

Primary sources

This page is drafted against the legislation below. Always check the current text of the law before acting.

Rent a Room scheme (GOV.UK)

Frequently asked questions

Do I need planning permission for an annexe?+

Building works for a garage conversion or outbuilding may be permitted development under GPDO 2015 Part 1 within size and height limits. However, using the resulting structure as a self-contained separate dwelling (own kitchen, bathroom, entrance) typically requires full planning permission for a new dwelling; the PD right covers the physical works, not the creation of a new home. Check with the local planning authority before proceeding.

Is my annexe separately assessed for council tax?+

A self-contained annexe with its own kitchen, bathroom, and entrance will typically receive a separate VOA council tax band and its own bill. Where it is occupied by a dependent relative aged 65+, severely mentally impaired, or substantially permanently disabled, the council tax on the annexe is reduced by 50% under LGFA 1992 s.11A.

Does private residence relief apply to an annexe?+

An annexe used as part of the main dwelling (ancillary use) qualifies for PRR on the same basis as the main house. An annexe let to a third party does not, any gain attributable to the annexe on disposal may be subject to CGT. Apportionment of gain is required where the use changed during the ownership period.

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