Garage conversion planning permission in London: when you need it and when you do not
Garage conversion planning permission is often not needed for an attached garage that becomes a bedroom, office or kitchen-diner. The exceptions are expensive when missed. This guide separates the cases that are free to proceed from the ones that need a condition lifted, a drawing submitted or a separate approval. It also sets out the building regulations work that applies in every case.
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Do you need garage conversion planning permission?
For most houses the answer is no. The Planning Portal says planning permission is not usually required, providing the work is internal and does not involve enlarging the building. The legal basis is section 55(2)(a) of the Town and Country Planning Act 1990. Works that affect only the interior of a building, or that do not materially affect its external appearance, are not development.
That rule covers the common project. A garage attached to or built into the house becomes a habitable room, and it remains part of the same dwelling, so there is no change in the planning use. The Planning Portal applies this to houses only. Flats, maisonettes, converted houses and other buildings sit outside its guidance.
The answer changes when something external happens, when a legal restriction applies, or when the finished space is not an extension of the family home. Each of those cases is set out below.
Which garage conversions need an application?
Nine situations cover almost every London garage, and the first few are usually free of any planning step.
Situation
Planning application?
Why
Integral or attached garage, internal work only
Usually not
Section 55(2)(a): interior-only works are not development
Garage door replaced by a wall and window
Often not, but depends on the street
Needs to avoid a material effect on external appearance; matching materials help
Original permission says the garage must stay available for parking
Yes, to vary or remove the condition
Article 3(4) of the GPDO: no permitted development contrary to a condition
Permitted development rights removed by condition or Article 4 direction
Only if the external changes need those rights
Interior-only works are not development under section 55(2)(a); the Planning Portal still advises checking with the council
Detached garage used as a home office or gym
Usually not, if incidental to the house
Use incidental to the house is not a change of use; Class E of Part 1 allows such outbuildings
Garage converted into a separate home or annexe let out
Yes, may be required whatever the work
The Planning Portal says so for a separate house, regardless of who will occupy it
Garage enlarged or extended during the conversion
Depends on the extension limits
Interior-only protection is lost once the building is enlarged
Garage in a flat or maisonette block
Check with the council
The Planning Portal guidance covers houses only, not flats or maisonettes
Listed building
Listed building consent may be required
Planning Portal garage conversion guidance
Sources: Planning Portal, Garage conversion; Town and Country Planning Act 1990, s.55(2)(a); Town and Country Planning (General Permitted Development) (England) Order 2015, art 3(4) and Sch 2 Pt 1 Class E. Read 13 October 2026. Always confirm with your council's decision notice for the house.
Why does a parking condition on the original permission matter?
Article 3(4) of the 2015 General Permitted Development Order says nothing in it permits development contrary to a condition on a planning permission granted otherwise than by the Order. If the permission that built your house, or a later one, says the garage shall be retained for parking, converting it breaches the condition, and a householder's usual freedoms do not rescue you.
A condition of this kind is invisible on site. The place to look is the decision notice on your council's planning register, not the deeds and not the estate agent's particulars.
The fix is an application under section 73 of the 1990 Act to vary or remove the condition. The planning practice guidance says the council must consider only the disputed condition. The original permission continues to exist whatever the outcome, and the planning practice guidance says a decision notice should restate the conditions that still apply.
How might a council judge the loss of a garage as parking?
Kingston upon Thames' Residential Design SPD, adopted in July 2013, was written for new garages and outbuildings and has no conversion test. It does show the dimensions this council expects of a new garage. A single garage should measure at least 5.3m by 3m inside and sit back at least 6m from the pavement. Any parking lost to an outbuilding should be replaced on site. The guide also asks for a front garden deeper than 4.57m, preferably 6m, if a space is created there. It says to contact the council's highways engineer so that any new crossover complies with the Highways Act 1980. Other boroughs set their own numbers, so read yours.
5.3m x 3m Single garage, internal size
6m Set back from pavement
4.57m+ Front garden for a space
What happens to the front of the garage?
Most conversions replace the garage door with a wall and a window, and that is the one external step that can attract attention. Section 55(2)(a) protects works that do not materially affect the external appearance, so the test is whether the new front looks like a different building. Matching brick, a window that lines up with the existing openings and a retained lintel line keep the change small.
Where the work is done under Class A of Part 1 of the 2015 Order, condition A.3(a) requires materials of a similar appearance to the existing exterior. Class A also applies tighter rules in conservation areas and other article 2(3) land. Cladding any exterior part in stone, artificial stone, pebble dash, render, timber, plastic or tiles is not permitted there. A conservation area house therefore needs its infill details checked before work starts.
Neighbours and the highway matter too. Kingston's guidance, for example, asks that any new crossover or dropped kerb complies with the Highways Act 1980, so a change to the drive is worth raising with the highways team.
What does building control look at in a garage conversion?
Building regulations approval is normally required for a garage conversion, even where planning is not, and the Planning Portal gives the working numbers for the walls, floor and ventilation.
Element
What the Planning Portal says
Number to design to
Garage conversion approval
Converting a garage, or part of one, into habitable space will normally require building regulations approval
Applies to part conversions as well
Infilled door foundations
Moisture-driven soil movement mainly occurs to a typical depth of about 0.75m, so foundations should go deeper
Deeper than 0.75m, and at least as deep as the nearest drain invert and neighbouring foundations
Solid floor
A new damp proof membrane and insulation are needed; the screed is likely to be in the order of 75mm thick with reinforcement mesh
75mm screed
Suspended timber floor
A damp proof course under the timber, insulation between joists
150mm minimum void above the existing concrete
Background ventilation
Trickle ventilation for each habitable room
8,000mm² in a multi-storey building, 10,000mm² in a single-storey building
Purge (rapid) ventilation
An opening window area measured against the floor area
1/10th of the floor area at 15 to 30 degrees; 1/20th above 30 degrees
Sources: Planning Portal, Garage conversion: building regulations, in-fill garage door, flooring and ventilation pages (the ventilation figures cite Approved Document F). Read 13 October 2026. Planning Portal figures are general guidance; the building control body sets the requirement for your building.
Which building regulations route does a garage conversion follow?
Converting an attached garage into a room of the house is building work to which the Regulations apply, and building control assesses compliance. Where the garage becomes a separate dwelling or flat, regulation 5 of the Building Regulations 2010 lists that as a material change of use, for example a building that is used as a dwelling where previously it was not, or that contains a flat where previously it did not.
That is why planning and building control give different answers on the same garage. Planning cares about use, appearance and parking. Building control cares about whether the room is dry, warm, ventilated and safe to escape from. Our guide to building regulations drawings explains the pack that building control expects.
How do you convert a garage with the right approvals in place?
The sequence below keeps the planning question and the building control question from contradicting each other.
1
Read the decision notice for the house
Find the planning permission that created the garage and look for a parking or garage-retention condition. This single check removes the most common surprise.
2
Check for Article 4 and designations
Search the council's Article 4 and conservation area maps for the address, and check whether the building is listed.
3
Decide what will change externally
A new wall and window at the front, a rear opening or a roof change each has a separate test. Keep external changes small and in matching materials.
4
Measure the garage and draw it
A measured survey gives the floor area for ventilation, the wall thickness for the infill and the floor level for the steps. The same drawings serve planning and building control.
5
Apply for what the checks require
That may be a section 73 application, a householder application, or a lawful development certificate that records the project is permitted, with building control approval alongside.
6
Keep the evidence
Retain the approved drawings and the completion certificate, because a buyer's solicitor will ask for both.
What mistakes catch garage owners out?
Never reading the decision notice
A retained-parking condition is invisible on site. It only appears on the council register, and it makes an otherwise permitted conversion a breach.
Converting only part of the garage
The Planning Portal says building regulations approval is normally needed for part of a garage turned into habitable space as well as the whole.
Letting the converted garage as a flat
A separate dwelling, with its own entrance and kitchen, is not part of the house. Planning permission may be required whatever work is done.
Treating a damp floor as a finish problem
A new membrane and insulation have to go in with the floor. The Planning Portal gives a screed in the order of 75mm for a solid floor.
Forgetting the drive
A converted garage can leave a drive with nothing to park beside. Borough guidance, such as Kingston's front garden depth tests, applies if you plan to move the parking.
What is the simplest way to settle garage conversion planning permission?
Read the decision notice, check the Article 4 and conservation maps, and keep the external change small. Those three steps settle garage conversion planning permission in most cases before any money is spent on drawings.
If the answer is not clear, send us the address and a photograph of the garage front. We check the constraints for free and tell you whether you need an application, a lawful development certificate or building control alone.
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Frequently asked questions
Do I need garage conversion planning permission for a bedroom?
Usually not. The Planning Portal says planning permission is not usually required, providing the work is internal and does not involve enlarging the building. You will need to apply if the original permission has a condition keeping the garage for parking, if the property is listed, or if external changes need permitted development rights that have been removed. Building regulations approval is separate and normally required.
How do I find out if my garage has a parking condition?
Search your council's planning register for the decision notice on the permission that built the house or garage, and read the numbered conditions. Look for wording that the garage shall be retained for parking or used only for that purpose. If you cannot find the notice, ask the planning team. A condition means the conversion needs a section 73 application to vary or remove it.
Does removal of permitted development rights stop a garage conversion?
Not for internal work, which is not development under section 55(2)(a). It can matter for the external changes. The Planning Portal says rights have sometimes been removed from some properties, and advises contacting the council, particularly on new housing developments or in a conservation area. Where an application is needed, a design that keeps the front looking like the rest of the street improves the odds.
Does replacing the garage door with a window need planning permission?
It can, if the change materially affects the external appearance. Section 55(2)(a) of the 1990 Act protects works that do not. A window and wall in matching brick that lines up with the neighbouring openings often falls within that protection, while a style that alters the street scene may not. Conservation areas add restrictions on cladding, so check before you order materials.
Do I need building regulations approval for a garage conversion?
Normally yes. The Planning Portal states that converting a garage, or part of a garage, into habitable space will normally require building regulations approval. Where the garage becomes a separate dwelling or flat, regulation 5 of the Building Regulations 2010 treats it as a material change of use. Approval covers the floor, walls, ventilation and drainage, among other matters. Planning permission does not replace it.
Can I turn a detached garage into a granny annexe?
Only with care. Using a detached garage as a home office, gym or playroom incidental to the house is generally not a change of use, and Class E of Part 1 of the 2015 Order permits such outbuildings. Sleeping accommodation lived in independently is different. The Planning Portal says that converting a garage into a separate house may need planning permission regardless of who occupies it, so check before it is occupied.
What foundation depth is needed when I block up the garage door?
The Planning Portal says moisture-driven soil movement mainly occurs up to about 0.75m, so foundations should be deeper than that. Excavation should normally reach at least the depth of the bottom of nearby drains or sewers, and at least the depth of an adjacent building's foundation. A structural engineer or your building control authority should confirm the figure for your ground.
What does a garage conversion floor need under building regulations?
Both a solid and a suspended floor need damp proofing and thermal insulation. On a solid floor the Planning Portal says a new damp proof membrane is needed and a reinforced screed is likely to be in the order of 75mm thick. On a suspended timber floor it asks for a minimum 150mm gap between the existing concrete and the timber, with insulation between the joists.
Will my council let me lose a garage parking space?
It depends on the borough. Councils test whether the loss harms the street, and some publish design standards that show what they expect of a garage. Kingston upon Thames' 2013 design guide, written for new garages, says a single garage should be at least 5.3m by 3m inside and that parking lost to an outbuilding should be replaced on site. It sets no conversion test, so check your own council's policy.
Can I get a certificate that my garage conversion is lawful?
Yes. A lawful development certificate under section 192 records that a proposed project is lawful, and one under section 191 records that existing work is. It is useful when a buyer or lender will ask for proof, or when you want the council's view before you start. It is not a substitute for building regulations approval, which is a separate certificate with different evidence.
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