A garage is one of the most underused rooms in a British home. Most are used for storage rather than cars, yet they sit there as fully-built, fully-roofed floor space — walls up, roof on, foundation laid — waiting to be turned into something you’d actually use every day. Converting one is usually the fastest, least disruptive way to add a room to a house, but it comes with a few decisions that are easy to get wrong if nobody explains them upfront: what kind of garage you have, whether you need planning permission, what it really costs, and whether it’s even the right move compared to extending or moving. Here’s what 20 years of doing this across Kent, Surrey, Sutton, Crawley and London has taught us.

Not All Garages Convert the Same Way

The single biggest factor in how your conversion goes isn’t the room you want — it’s the type of garage you’re starting with. This decides your planning risk, your structural work, and a good chunk of your budget before design even begins.

Garage type	What’s usually involved	Planning risk
Integral (built into the house footprint)	Mostly internal work — infill the door opening, insulate, add services	Lowest — almost always Permitted Development
Attached (joined to the house by a wall or roofline)	Similar to integral, plus roof and wall junction checks	Low, unless a planning condition applies (see below)
Detached (separate structure)	Often needs new openings, upgraded foundations, and sometimes a change-of-use assessment	Higher — full planning permission is common
Single vs double garage	A double gives you room for two zones (e.g. office + storage, or bedroom + en-suite) for roughly the cost differential of materials and services, not double the labour	Same rules apply as above; size doesn’t change the planning route, only the build cost

Four Things to Check Before You Get Attached to a Plan

Before any design work starts, it’s worth checking these yourself, or asking a builder to check them at survey stage:

1. Structural condition. Garages are typically built to a lower structural standard than the main house — shallower foundations, thinner single-skin walls, and lighter roof structures are the norm. A structural engineer’s assessment tells you upfront whether you’re looking at a straightforward infill or a more involved rebuild.
2. Ceiling height and floor level. Garage floors often sit lower than the house’s ground floor, and ceiling heights can be tight once insulation and a proper floor build-up are added. This affects whether the room will comfortably work as a bedroom (which needs an escape window) versus a lower-headroom use like storage or utility.
3. Damp and ventilation history. Garages are unheated, uninsulated spaces by design, so damp is common. It isn’t a dealbreaker, but it does add to the Building Regulations scope.
4. Title deeds and planning history. This is the one people miss. Check your property’s original planning decision notice and title deeds for two things: a restrictive covenant on the garage’s use, and a planning condition requiring the garage to be retained for off-street parking. Both are common on newer estates and are the single biggest reason a straightforward-looking conversion turns out to need a planning application.

Planning Permission: The Part People Worry About Most

Converting an integral or attached garage into habitable space is normally treated as an internal alteration rather than ‘development’, because you’re not adding volume, creating a separate dwelling, or materially changing the external appearance. In practice, that means most conversions in our coverage area go ahead without a planning application at all.

The exceptions are worth knowing before you fall in love with a design:

• Your garage is detached and the conversion involves a significant change to its external appearance
• Your original planning permission included a condition requiring the garage to be retained for parking — common on newer housing estates across Kent, Surrey and Crawley
• You’re changing the garage door to a window, door or wall facing the road, altering the frontage
• Your property is in a conservation area, is listed, or sits under an Article 4 direction removing Permitted Development rights — worth checking specifically in parts of South London, where Article 4 directions are more common
• You intend to create a fully self-contained unit with its own kitchen, bathroom and entrance, which planning authorities may treat as a separate dwelling

Even when permission isn’t needed, it’s worth applying for a Lawful Development Certificate (typically £124–£310 in 2026, taking around 6–8 weeks). It’s not compulsory, but it’s the document a conveyancing solicitor will ask for when you sell — without it, buyers or their solicitors may ask for indemnity insurance or try to knock money off the price.

Building Regulations Apply Whether or Not Planning Does

This catches people out: Building Regulations approval is required for every garage conversion, no exceptions, because you’re turning an unheated space into a habitable room. Building Control will check structural safety (Part A), fire escape provisions if it’s a bedroom (Part B), damp-proofing (Part C), ventilation (Part F), insulation and thermal performance (Part L), and any new electrical work (Part P). Fees typically run £360–£1,200 depending on your council and the complexity of the job.

What Does a Garage Conversion Actually Cost in 2026?

Costs vary by finish level and scope more than by location within our coverage area. As a general guide:

Conversion type	Typical cost range	Typical timeline
Basic (home office, utility, storage upgrade)	£8,000–£14,000	2–4 weeks
Mid-range (bedroom or playroom, no en-suite)	£14,000–£22,000	4–6 weeks
High-spec (bedroom with en-suite, or self-contained annexe)	£22,000–£35,000+	6–10 weeks, longer if planning permission is required

These figures cover structural work, insulation, plastering, electrics and a basic fit-out. Kitchens, en-suites, or premium finishes push costs toward the top of the range. Detached garages typically cost more than integral ones, mainly because of the extra work involved in extending services — water, drainage, heating — from the main house.

Does It Actually Add Value — and Is There a Catch?.

A well-executed garage conversion is commonly cited as adding up to 20% to a property’s value, particularly in areas where floor space commands a premium. Treat that as a general market guide rather than a guarantee — it depends on how the finished room compares to similar homes on your street. Two things are worth weighing against the upside:

• Parking. If off-street parking is in short supply on your street, losing the garage may slightly reduce appeal to some buyers, even as the extra room adds value.
• Insurance and mortgage. Notify your buildings insurer once the room becomes habitable — the risk profile can change. If you have a mortgage, check whether your lender’s terms require notification of structural alterations.

On the upside, a properly insulated conversion can improve your property’s EPC rating, which is increasingly something buyers and lenders pay attention to.

Garage Conversion vs Extension vs Moving House

	Garage conversion	Single-storey extension	Moving house
Typical cost	£8,000–£35,000	£25,000–£60,000+	Stamp duty, agent fees, legal costs — often £15,000–£40,000+ before any price difference on the new home
Typical timeline	2–10 weeks	3–6 months	3–6 months, often longer
Planning permission	Usually not required	Often required or needs a Prior Approval route	Not applicable
Disruption	Low — existing walls, roof and foundation are reused	Moderate to high — groundworks, new structure	High — full house move

If you’re weighing up whether to convert, extend, or move, a garage conversion is usually the fastest and lowest-risk way to add a room — provided the garage isn’t your only off-street parking and there’s no retained-parking condition attached to your planning history.

What People Actually Build

The most common conversions we see across Kent, Surrey, Sutton, Crawley and London:

• Home office — by far the most requested use since 2020; a separate entrance from the garden or driveway, where the layout allows, makes it feel genuinely separate from the house
• Bedroom with en-suite — popular for growing families or as a self-contained space for older children or visiting relatives
• Home gym — rubber flooring, mirrored walls and extra ventilation are the main additions on top of a standard conversion
• Playroom or snug — often the lowest-cost option since fewer services are needed
• Utility or laundry room — frees up space in the kitchen; needs additional plumbing and drainage factored into the quote
• Self-contained annexe — the most involved option, and the one most likely to need full planning permission if it includes its own kitchen and entrance

Thinking About Converting Your Garage?

If you’ve read this far, you probably already have a good sense of whether your garage is a strong candidate. The next step is a proper site survey — someone who can check your specific structure, your planning history, and give you a fixed price rather than a rough guide. That’s exactly what we do at the first consultation, and it’s free.