The short answer
A garage conversion is usually cheaper, quicker and less disruptive than an extension — typically £6,000–£20,000 against tens of thousands for an extension — and it normally avoids a planning application, but you are limited to the existing footprint. An extension adds more, and a wider choice of, space and can transform a home, but it costs more, usually takes longer and is more likely to need planning permission. The right choice depends on how much space you need, your budget, and whether you can spare the garage.
Converting the garage and building an extension are the two common ways to add living space, and they suit different needs. A conversion reworks space you already have; an extension creates new space. This guide compares them on cost, space gained, planning, disruption and resale so you can decide which fits your home. These are general pointers, not advice for your specific project. For conversion figures, see the main cost guide; for the wider decision, see is a garage conversion worth it.
Conversion vs extension at a glance
- Conversion cost £6,000–£20,000
- Extension cost Usually higher
- Planning Conversion often avoids it
- Disruption Lower for a conversion
- Space gained Extension can add more
- Footprint Conversion keeps existing
Cost and disruption
On cost, a conversion usually wins: the structure, roof and foundations already exist, so you are mainly paying to make the space habitable rather than to build something new. A typical conversion runs £6,000–£20,000, while a single-storey extension commonly costs several times that. A conversion is also quicker and less disruptive, with much of the work inside an existing shell. An extension involves groundworks, new walls and a new roof, so it takes longer and is messier to live through. These are typical illustrations, not quotes — get itemised figures for your project.
Space, planning and the garage trade-off
An extension can add more space, and space in the shape you want — a larger kitchen-diner, for instance — whereas a conversion is bounded by the garage footprint, usually around 13–18m² for a single garage. On planning, many conversions fall under permitted development and need only building regulations, while extensions are more likely to need a planning application; check the planning permission guide. The other trade-off is the garage itself: a conversion removes it, so if you value the parking or storage, an extension that keeps the garage may suit you better.
| Factor | Garage conversion | Extension |
|---|---|---|
| Typical cost | £6,000–£20,000 | Usually several times more |
| Space added | Existing footprint (~13–18m²) | Can be larger and bespoke |
| Planning permission | Often not needed | More likely needed |
| Disruption & time | Lower, quicker | Higher, longer |
| The garage | Lost | Can be kept |
Which should you choose?
If you need a modest amount of extra space at a lower cost and can spare the garage, a conversion is often the sensible choice. If you need significantly more space, or space the garage cannot provide, and your budget and plot allow, an extension may be worth the extra cost — and you can sometimes keep the garage too. Both must meet building regulations and, done well, can support resale value. This is general information; the right answer depends on your home, budget and plans, so seek local advice and use a garage conversion specialist who handles building control.
Compare garage conversion quotes
Weighing a conversion against an extension is easier with real costs in front of you. Compare itemised quotes from FMB-registered or building-control-approved specialists in your area.
Frequently asked questions
Is a garage conversion cheaper than an extension?
Usually, yes. A conversion reuses the existing structure, roof and foundations, so it typically costs £6,000–£20,000, while a single-storey extension commonly costs several times more. An extension adds more space, which can justify the higher cost where you need it.
Does an extension always need planning permission?
Not always — some extensions fall under permitted development — but they are more likely to need a planning application than a conversion, which often does not. Both must meet building regulations. Check the planning permission guide and your local authority.
Can I extend and keep my garage?
Often, yes — an extension can add space elsewhere while leaving the garage intact, which suits homes where parking or storage is valued. A conversion, by contrast, uses the garage itself. Weigh how much you rely on the garage when choosing.
Sources & further reading
- Federation of Master Builders (FMB) — conversions, extensions and registered builders
- Planning Portal — permitted development for conversions and extensions
- RICS — guidance on home improvements and value
- GOV.UK / Building Regulations Approved Documents — standards for habitable rooms
This is general information, not advice for your specific project. The right choice depends on your home, budget, plot and plans, so seek local advice. The work should be carried out by an FMB-registered or building-control-approved specialist. We are an independent information and introduction service, not a builder.