Garage conversion architect for homes across London

Do you need planning permission to convert a garage?

Usually not. Converting an attached garage into habitable space is generally permitted development provided the work is internal and does not enlarge the building, and provided the front garage door is replaced with a window or wall that matches the house. That last condition is where schemes fail: an infill panel in a different brick, or a window whose proportions ignore the rest of the elevation, changes the appearance of the principal elevation and takes the work outside permitted development.

Permission is required in four situations that are common across London. The property may be in an Article 4 area where the council has withdrawn the right — a number of boroughs operate directions specifically aimed at front-elevation alterations and the loss of off-street parking. The garage may be detached, in which case converting it to habitable accommodation is a change of use rather than an internal alteration. The property may be listed or in a conservation area. Or a planning condition on the original estate permission may require the garage to be retained for parking, which is routine on 1980s and 1990s developments and survives any change of ownership.

Where the work is permitted development we recommend a Lawful Development Certificate at £129. On a garage conversion it matters more than usual, because the change is visible from the street and a future buyer will want documentary proof it was lawful.

Why is building control the hard part of a garage conversion?

A garage was built as an unheated store. Every element that was adequate for that purpose is inadequate for a habitable room, and the conversion is a full building regulations job even though nothing is being added.

• Floor — most garage slabs sit 100 to 150mm below the house floor level, have no damp-proof membrane and no insulation. The usual answer is an insulated build-up over the existing slab, which must reconcile the level difference at the connecting door without creating a step that fails Part K.
• Walls — single-skin or unfilled-cavity construction is common. Meeting Part L normally means an insulated internal lining, which costs 75 to 100mm off each wall and has to be detailed to avoid interstitial condensation.
• Damp — a garage frequently has no damp-proof course at all, or one bridged by an external path. This is the single most common reason a converted garage feels cold and smells damp two winters later.
• Front infill — the new wall below the window needs a proper foundation, a cavity tray and a lintel where the garage door opening was, not simply blockwork built off the slab edge.
• Ventilation and heating — background ventilation to Part F and an extension of the heating system sized for the added volume.
• Fire and escape — where the garage adjoins an integral space or a habitable room becomes an inner room, the escape route through the house has to be reassessed.

We produce the construction drawings, the specification and the compliance schedule against each Approved Document, and coordinate the structural engineer where the front infill needs a designed lintel or the roof structure is being altered.

Which garages are actually worth converting?

Three measurements taken at survey decide whether a garage conversion produces a room anyone wants to use, and they are worth checking before any money is spent on design.

• Internal width — a pre-1970 London single garage is frequently only 2.4 metres wide internally. Take 100mm off each side for an insulated lining and the finished room is 2.2 metres, which works as a study or utility but not as a bedroom.
• Existing head height — the floor build-up typically consumes 100 to 150mm. A garage with a 2.3 metre soffit ends up close to the practical minimum once the floor is raised.
• Relationship to the house — an integral garage opening directly onto a hallway converts cleanly. A garage reached only through the kitchen creates an inner room, which changes the escape strategy and often forces a second door or window.

Where the width or height fails, the better answer is usually to demolish and rebuild as a proper single-storey extension. That is a planning application rather than a certificate, and the build cost rises to extension rates, but it produces a room sized for its purpose rather than a compromise dictated by a 1960s car.

What does a garage conversion cost and what does it add?

Build costs at 2026 London rates run roughly £1,100 to £1,700 per square metre for a single garage conversion — well below the £2,200 to £3,000 of a new extension, because the shell exists. A typical 15 square metre single garage therefore lands between £17,000 and £26,000 including finishes, with the variables being the floor build-up, whether the roof needs work, and how far the services have to be extended.

Against that, add the £129 certificate fee or £258 householder application where permission is needed, and £600 to £1,100 of building control charges. The drawings at £840 are a small proportion of a project where the risk is entirely technical.

The trade-off worth thinking about honestly is parking. In outer London boroughs with controlled parking zones, losing the only off-street space can affect saleability more than the added room adds. In inner boroughs where the garage is too narrow for a modern car anyway — which describes most pre-1970 London garages — the calculation is straightforward.

Garage conversion questions we hear most