Granny flat

A granny flat is a self-contained home within or beside a main house, built or adapted so that a relative, traditionally an elderly parent, can live independently close to family. It has no separate legal definition: in law it is an annex, and the Council Tax (Reductions for Annexes) (England) Regulations 2013 treat it as a separate dwelling within a single property.

Granny flats take the form of converted garages, loft or basement conversions, side extensions and detached garden buildings. The name describes who lives there, not how the space is built.

What is a self-contained flat?

A self-contained flat is a set of rooms where the occupants have their own kitchen, bathroom and toilet, used by nobody else, and normally their own entrance. The Housing Act 2004, section 254(8) defines it as separate premises forming part of a building in which a toilet, personal washing facilities and cooking facilities are all available for the exclusive use of its occupants.

A granny flat is self-contained when it has:

• Own entrance: a front door the occupant can use without passing through the main house.

• Own kitchen: a hob or cooker, sink and space to store and prepare food.

• Own bathroom: a toilet and a shower or bath, not shared with the main household.

Granny flat vs annex vs self-contained flat

The three terms overlap but are not interchangeable.

Annex: the umbrella term for any secondary living space on the same plot as a main house. An annex can be fully self-contained or can share facilities, such as a bedroom and shower room that rely on the main house's kitchen.

Granny flat: an annex occupied by a relative. Most are self-contained, because the point is independent living.

Self-contained flat: any home with its own exclusive kitchen and bathroom, whether a granny flat, a converted flat in a house or a purpose-built flat in a block.

What granny flats are used for

The original use is housing an elderly parent who needs support but wants their own front door. Families now use granny flats just as often for adult children saving for a deposit or for a live-in carer. Some owners let them to unrelated tenants, which changes the rules considerably.

Planning, building regulations and council tax in brief

Planning: permitted development rights for outbuildings exclude primary living accommodation such as a bedroom, bathroom or kitchen, so a self-contained granny flat in the garden usually needs planning permission.

Building regulations: any granny flat with sleeping accommodation needs building regulations approval. The annex entry covers both in detail.

Council tax: a self-contained granny flat usually has its own council tax band. The bill is halved when a relative lives there, and is fully exempt for a dependent relative, such as one aged 65 or over, under Class W of the Council Tax (Exempt Dwellings) Order 1992.

Stamp duty: Multiple Dwellings Relief, which once reduced stamp duty on a house with a granny flat, was abolished for purchases completing on or after 1 June 2024.

Letting out a granny flat

Once a granny flat houses a tenant rather than family, it becomes a rental property with the same duties as any other let: an EPC, gas and electrical safety checks, alarms and deposit protection. From working with self-managing landlords, we see the same mistake repeatedly: owners treat a granny flat as an informal family space and only discover the planning condition limiting it to family use when they come to let it.

The tenancy type depends on the layout. A tenant in a detached garden flat while you live in the main house usually holds an assured tenancy; someone in an attached flat who shares your kitchen is closer to a lodger. Landlords who start letting one through August tend to find that rent, certificates and renewal dates for a single granny flat need the same tracking as a full buy-to-let.

Frequently asked questions

What is the difference between a granny flat and an annex?

A granny flat is a type of annex: one used to house a relative. "Annex" covers any secondary living space linked to a main home, whoever lives there and whether or not it is self-contained. The same planning and council tax rules apply to both.

Can you rent out a granny flat?

Yes, if the planning permission allows it. Many granny flats are approved as ancillary to the main house, with a condition restricting occupation to the household or family, and letting to an unrelated tenant would breach it. Check the decision notice before advertising, and apply to vary the condition if needed.

Do you need planning permission for a granny flat?

Usually, yes. A garden building used as a bedroom, bathroom or kitchen falls outside permitted development, and converting part of the house into a separate home is normally a material change of use.