Extensions over a garage

An over-garage extension adds a new first-floor room on top of an existing attached garage, usually a bedroom, home office or en-suite. Because the footprint already exists, you gain a room without losing any garden.

The key question is whether the garage walls and foundations can carry another storey. Many 1960s to 1990s garages were built with a single skin of brick or shallow footings, so a structural survey comes first and some garages need strengthening or rebuilding.

What is included

• Structural survey of garage walls and foundations
• Design and householder planning application
• Strengthening or rebuilding the garage walls if needed
• New floor structure, walls and roof
• Opening into the existing first floor
• Insulation, electrics, heating and finish

Who it suits

• Detached and link-detached houses with an attached garage
• Families needing a bedroom without losing garden
• Homes where the landing can connect to the new room

Design advice

Fitting the new room to the existing landing is the planning puzzle inside the house. We design the connection first, then the roof, so the extension does not end up with awkward steps or a corridor through a bedroom.

How much does it cost?

National guide prices including VAT at 20%. Build cost only; design, structural and council fees are extra. Your area page shows prices adjusted for your region.

Planning rules across the UK

England

In England any side extension over one storey, including a room built over a side garage, needs a householder planning application. The fee is £548 from 1 April 2026 and councils aim to decide within 8 weeks.

Wales

In Wales a two-storey side extension must be at least 10.5 m from the side boundary to be permitted development, which few houses can meet, so a planning application to the council is the usual route for a room over a garage.

Scotland

In Scotland, householder permitted development rules (Class 1A for single-storey ground-floor extensions and Class 1B for extensions of more than one storey) allow some smaller extensions without a planning application, within limits on depth, height and distance from the boundary. Conservation areas and listed buildings are more restricted. Separately, almost every extension needs a building warrant from the council before work starts.

Northern Ireland

In Northern Ireland the Planning (General Permitted Development) Order 2015 lets some single-storey rear extensions go ahead without planning permission, up to 3 m on a semi-detached or terraced house and 4 m on a detached house, within height and boundary limits. Larger, side and two-storey extensions normally need planning permission from the council, and building control approval is separate.

Building regulations and neighbours

Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.

In England and Wales, if the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations. Scotland and Northern Ireland have no Party Wall Act.

Questions about extensions over a garage