Get a fixed price: Garage conversion cost UK and what to insist on
A single garage conversion typically costs between £10,000 and £20,000 for a standard 16m² space, working out at roughly £625 to £1,250 per m². Wider industry data puts the full project range at £7,000 to £32,000, averaging around £13,500. Costs climb fast once you add plumbing, a bathroom, or structural repairs to bring the space up to habitable standard.
TL;DR:
Costs vary widely depending on the scope, with basic conversions around £7,000 to £20,000 and full-service projects reaching £32,000, especially if adding wet services or finishes.
Structural elements like foundation infill and damp-proofing are major cost drivers, often adding several thousand pounds if existing foundations are shallow or moisture issues are present.
Integral or attached garages are generally cheaper to convert than detached ones due to shared walls and services, and adding bathrooms significantly increases costs due to drainage and waterproofing needs.
A detailed survey of foundation depth, drainage capacity, and asbestos presence can influence budget estimates and prevent surprises during construction.
Strict building regulations still apply, requiring proper insulation, damp-proofing, and fire safety compliance, which may not be fully included in low-cost quotes.
Table of Contents
Price ranges and what they mean
Cost guides rarely agree on a single figure, and that’s not a flaw in the research: it reflects how differently two “garage conversions” can be specified. Checkatrade’s 2026 guide gives a typical range of £10,000 to £20,000 for a 16m² garage, with a per-m² rate of £625 to £1,250. The Federation of Master Builders reports a broader spread of £7,000 to £32,000, averaging roughly £13,500 for the same 16m² benchmark. Neither figure is wrong. They simply capture different points on the same spectrum, from a basic insulated room with sockets and a radiator through to a fully serviced space with a bathroom and bespoke finishes.
The gap between “low” and “high” in any quote usually comes down to three things: how much structural work the infill wall needs, whether you’re adding wet services, and the quality of fixtures and joinery. A conversion that stops at insulation, plasterboard, and a lick of paint sits at the bottom of the range. One that adds an en-suite, underfloor heating, and fitted storage sits at the top, even though both started life as the same size garage.
Applying the low, typical, and high per-m² multipliers to different garage sizes gives you a working budget before you get quotes:
12m² garage: roughly £7,500 at the low end, £11,000 typical, £15,000 at the high end.
16m² garage: roughly £10,000 low, £14,000 typical, £20,000 high, consistent with the Checkatrade and FMB benchmarks above.
30m² garage (double): roughly £18,750 low, £27,000 typical, £37,500 high, reflecting the larger footprint and proportionally higher services cost.
These are starting points, not fixed prices. A survey of your specific garage, its foundations, and its intended use will always narrow the range further.
Detailed cost breakdown: labour, structural work and finishes
A fair quote should let you see where the money goes, not just the total. Most garage conversions break down into a fairly consistent set of line items, though the proportion each one takes up shifts depending on scope.
Labour and site management: typically the largest single share, covering trades’ time and supervision across the build.
Structural works: infilling the garage door opening, which may need new foundations or lintels depending on what’s already there.
Insulation and damp-proofing: upgrading walls, floor, and roof to meet thermal and moisture standards.
Electrics: new circuits, sockets, lighting, and consumer unit capacity checks.
Plumbing and heating: radiators or underfloor heating as standard, with a significant jump if you’re adding a bathroom or kitchenette.
Windows and doors: replacing the garage door with a wall, window, and an internal door matching the rest of the house.
Flooring: a raised insulated floor or new insulated slab, depending on existing floor levels.
Finishes: plastering, decoration, skirting, and architrave to match the main house.
Checkatrade’s data shows conversion costs typically run well below full extension costs on a per-m² basis, with extensions reaching £1,800 to £3,000 per m² against a conversion’s £625 to £1,250. That gap exists because you’re reusing an existing structure rather than building new walls and foundations from scratch, though it narrows quickly once structural infill or wet services enter the picture.
The most expensive individual items tend to be structural infill where existing foundations are shallow, damp remediation where the garage has no damp-proof course, the floor build-up needed to bring levels in line with the rest of the house, and any plumbing that requires new drainage runs for a bathroom. Each of these can add several thousand pounds to what looks, on paper, like a straightforward conversion.
Factors that influence cost
Not every garage conversion starts from the same point, and the type of garage you have changes the maths before you even get to finishes.
Integral or attached garages usually cost less to convert because they already share walls and services runs with the house, cutting down on new drainage and heating pipework.
Detached garages cost more, since heating, water, and often electrics need to be extended from the main house, sometimes underground.
Adding a bathroom or en-suite brings drainage, ventilation, and waterproofing requirements that a simple bedroom or office conversion doesn’t need, and is one of the biggest single cost jumps in this list.
Site access affects labour time and skip or material delivery costs, particularly for garages set behind narrow side passages.
Existing foundation depth determines whether the infill wall needs new footings or can use lintel-supported construction, a detail worth confirming early since it can shift the structural budget significantly.
Local labour rates also vary, and a quote from a contractor working across London and the surrounding counties may differ from one further afield, even for an identical specification.
Pro Tip: Ask your surveyor to check the garage’s existing foundation depth before you finalise a budget. It’s one of the few details that can swing the structural cost by thousands either way.
Permissions, building regulations and compliance essentials
Converting a garage internally, without extending the building’s footprint, usually doesn’t need planning permission. There are exceptions worth checking with your local planning authority before you commit to a budget: if the conversion creates a separate dwelling, if permitted development rights were removed when the house was built or previously altered, or if the property sits in a conservation area or is listed.
Building Regulations, however, apply regardless of whether planning permission is needed. Redbridge Council’s guidance sets out the core requirements clearly: structural stability, damp-proofing, insulation, ventilation, and fire safety all need to be addressed for the space to count as habitable. This is also where a cheap quote can mislead: if a contractor’s price doesn’t cover these items, you’re not comparing like with like.
Before you finalise a budget, build a short pre-start checklist:
Asbestos check: older garages may contain asbestos in roofing sheets or floor tiles, which needs safe removal before work starts.
Drainage survey: confirm where existing drainage runs before planning a bathroom or kitchen addition.
Party wall advice: attached and integral garages sharing a wall with a neighbouring property may trigger party wall obligations.
Building control sign-off: confirm your contractor will submit the completed work for building control approval, not just carry out the works.
Programme, typical timescales and hidden cost risks
A basic garage conversion, insulation, electrics, flooring, and decoration with no structural changes, typically takes 2 to 4 weeks from start to finish. Add structural infill work, new drainage for a bathroom, or significant damp remediation, and the programme can stretch well beyond that window.
A proper pre-start survey is the single best way to avoid surprises mid-build. It should identify:
Damp, particularly where the garage has no existing damp-proof course.
Asbestos, common in garages built before the 1980s.
Foundation depth, which determines the structural approach for the infill wall.
Existing drainage capacity, relevant if you’re adding wet services.
It won’t cover a major structural surprise, but it absorbs the smaller variations that almost every conversion throws up once the walls are opened.
How to budget, compare quotes and get an accurate fixed price
Getting comparable quotes starts before you contact a single contractor. Prepare a brief that states the intended use of the room (bedroom, office, bathroom), any services you want added, and, where possible, basic drawings or measurements.
Share the same brief with every contractor so quotes reflect identical scope, not different assumptions about what’s included.
Ask for an itemised, fixed quote, not a rough estimate, covering labour, materials, structural work, and compliance sign-off separately.
Request the proposed wall and floor build-up in writing, including target U-values, so you can compare thermal performance across quotes.
Confirm VAT treatment, payment stages, and what happens if the scope changes mid-project.
Ask about insurance, party wall handling, and how service disconnection and reconnection (water, electrics) is managed.
If one quote comes in well below the others, ask what it excludes before assuming it’s the better deal. A missing damp-proofing allowance or an unspecified U-value target often explains the gap, and local authority guidance consistently warns that the lowest price is only meaningful when every contractor is quoting for the same compliance scope.
Pro Tip: Keep a written record of every quote’s inclusions and exclusions side by side. It takes ten minutes and stops you comparing a fully compliant conversion against one that quietly skips the parts building control will ask about.
Cost breakdown by build stage
Breaking the same costs down by construction stage, rather than by trade, helps when you’re staging payments. Structural work, infilling the garage opening and any foundation strengthening, typically happens first and carries the highest single-stage cost where existing foundations are shallow. Insulation and damp-proofing follow, addressing walls, floor, and roof to meet the thermal and moisture standards set out in CNC’s building control guidance, which recommends a new infill wall achieve a U-value around 0.18 W/m²K and suggests existing walls may need upgrading to around 0.30 W/m²K.
Electrics and plumbing come next, with heating (radiators or underfloor systems) usually installed alongside them. Windows and doors, replacing the garage door with a wall and matching window and door units, follow the first-fix stage. Flooring, whether a raised timber floor or a new insulated slab, is fitted before final decoration. Finishes, plastering, painting, skirting, and any built-in storage, complete the project. Asking your contractor to structure the quote in this order makes it far easier to track progress against payment stages.
How a garage conversion affects property value
A converted garage adds usable floor space, and that’s generally viewed positively by buyers looking for an extra bedroom, office, or family room. Whether it adds resale value depends heavily on what you lose in the process: if the property relies on off-street parking or garage storage in an area where that’s scarce, removing it can offset some of the gain from the extra room.
The quality of the conversion matters too. A room finished matching the rest of the house, proper insulation, matching flooring, and compliant electrics, reads as genuine living space to a valuer or buyer. A conversion that still looks and feels like a garage with carpet laid over it tends not to add the same value, regardless of the room’s intended use. Keeping the completed work compliant with Building Regulations also matters at sale: a missing certificate can complicate a transaction even if the room itself looks finished.
Financing a garage conversion
Most homeowners fund a garage conversion through savings, a further advance on their existing mortgage, or a secured home improvement loan. A further advance is often the cheapest route if you have sufficient equity, since it’s usually priced closer to your existing mortgage rate than an unsecured loan.
Some homeowners use a remortgage timed to coincide with the end of a fixed-rate deal, rolling the conversion cost into the new mortgage. Others use a personal loan for smaller-scope conversions where the total sits comfortably within typical unsecured lending limits. Whichever route you choose, it’s worth getting a firm, itemised quote first: lenders offering home improvement finance will often ask for a specification and cost breakdown before releasing funds, which is another reason a vague estimate causes delays later.
Cost variations by material and finish quality
The same 16m² garage conversion can cost meaningfully different amounts depending on the specification you choose, even with an identical layout. Standard-grade insulation, laminate flooring, and painted plasterboard sit at the lower end of the ranges discussed earlier. Upgrading to engineered timber flooring, higher-specification insulation boards, or fitted joinery pushes the same project toward the upper end, even without any change to the room’s size or function.
Windows and doors are a good example: a standard uPVC window and internal door cost considerably less than a timber-framed window matched to a period property’s existing joinery. Heating choices matter too. A single radiator on the existing central heating circuit costs far less than a dedicated underfloor heating system, which usually needs its own manifold and floor build-up. None of these choices are wrong, but they explain why two conversions of the same size can land at very different points within the ranges quoted at the start of this guide.
Publisher perspective: how EvoStruct approaches accurate costing
Vague estimates are the biggest source of frustration in garage conversions, not the building work itself. EvoStruct’s approach reflects what this guide recommends: a site survey, a fixed quote delivered within 24 hours, and documented change control if anything shifts once work starts. It’s live virtual tours of active projects, including work shown on its garage conversion pages, let homeowners see workmanship and project management before committing, rather than relying on a portfolio of finished photos alone. A good contractor process should always give you that level of visibility.
— Florin
How EvoStruct can help with your garage conversion
EvoStruct’s Garage Conversions service starts from £14,000 and covers homeowners across Islington, Harlow, Chigwell, and the wider Greater London area.
If you’re ready to move from research to a real number, request a site survey and you’ll get a detailed, itemised quote within 24 hours. Have your garage’s approximate size, intended use, and any drawings ready before your survey to speed things up. Get in touch through EvoStruct’s inquiry page to arrange yours.
Sources
FAQ
Do I need permission to convert my garage into a room?
Usually not, since internal conversions that don’t enlarge the building typically fall outside planning permission requirements, according to Planning Portal guidance. Exceptions apply if the conversion creates a separate dwelling, if permitted development rights were previously removed, or if the property is listed or in a conservation area. Building Regulations approval is still required regardless of planning status.
Is garage conversion worth it?
It’s generally worth it when the extra room adds genuine living space you need, and when the finished work meets Building Regulations standards for structural, damp, insulation, and fire safety. The value it adds depends on local demand for parking versus extra rooms, and on how well the finish matches the rest of the house.
Is it cheaper to convert a garage or build an extension?
A garage conversion is typically cheaper, running at roughly £625 to £1,250 per m² compared with an extension’s £1,800 to £3,000 per m² on the same guide. The saving comes from reusing existing walls and foundations rather than building new ones from scratch.
Do you have to pay council tax on a converted garage?
A converted garage that becomes part of the main house’s habitable floor area is generally assessed as part of the existing council tax band rather than taxed separately. It’s worth confirming with your local council once the conversion is complete, since practices can vary by authority and by how the space is used.
Recommended
Comments