Garden Room Cost Per m² in the UK: What Drives the Price

How much does a garden room cost per square metre in the UK? Cost per m² is a genuinely useful way to sanity-check quotes because it strips out the size variable — but it's also easy to misuse, because two "£1,200/m²" quotes can include completely different specifications. This guide explains the general market ranges you'll see quoted across the UK, what actually drives the gap between cheap and expensive garden rooms, and how the LouMil pricing model works if you want a real figure for your own project.

General UK Market Ranges (Informational)

Across the wider UK garden room market, published price-per-m² figures broadly cluster into three bands, though exact numbers vary by region, supplier and specification:

• Budget / flat-pack kits: the lowest band — minimal insulation, basic materials, often self-assembly, no electrics included
• Mid-range, professionally installed builds: a middle band covering insulated, plastered, electrically wired rooms installed by a company rather than self-built
• Premium, high-specification builds: the top band — higher-spec insulation, bespoke design, premium doors and windows, and a fuller finish

These are general market observations, not LouMil prices, and they'll vary by region and supplier — treat any specific £/m² figure you see quoted (including ones on this page) as indicative only, and always check exactly what's included before comparing two numbers.

Why Cost Per m² Is a Blunt Tool

The reason two similarly-sized garden rooms can carry very different price tags isn't usually the size — it's what's included. A quote that looks cheap per square metre may exclude insulation, electrics, a proper base, or plastering and list them as "extras" once you've committed. A genuinely comparable quote needs to spell out the same list of inclusions on both sides before the per-m² figure means anything.

What Really Drives the Cost of a Garden Room

• Insulation and internal finish: a plastered, insulated room costs more to build than a shell with exposed timber or OSB walls
• Windows and doors: sliding or bifold doors cost more than standard French doors; more glazing costs more than less
• Electrics and heating: a full electrics package with sockets, lighting and a heater adds cost but is central to year-round usability
• Cladding: composite cladding costs more upfront than standard timber shiplap, but needs less ongoing maintenance
• Base and groundworks: ground screws versus a concrete base, and how easily the site can be accessed, both affect cost
• Size and shape: larger buildings often have a lower cost per m² because some costs (delivery, base groundwork) don't scale directly with floor area; unusual shapes like an L-shape typically add a percentage over an equivalent rectangle

How the LouMil Pricing Model Works

Rather than a single all-inclusive £/m² figure, LouMil garden rooms start from a base specification — the structure, external cladding (timber shiplap as standard), an EPDM rubber roof, French doors, two full-height windows, plus delivery and installation — from £9,000 inc. VAT. From there, you choose the options that suit how you'll use the room: insulation & plastering, flooring, electrics and a heater, door upgrades such as sliding or bifold doors, composite cladding, ground screws, and decorating. Nothing beyond the base specification is assumed to be included, and the price you see reflects exactly what you've chosen — there's no separate LouMil size-tier price list, because the right specification (and therefore the right price) genuinely differs from one project to the next.

The most accurate way to see a real number for your project is to use our calculator: choose your room, build your specification, and see your price. For a broader look at how garden room pricing works before you start speccing, see our garden room price guide.

Garden Room vs House Extension

Extensions and garden rooms solve different problems, and comparing them purely on cost per m² misses some real differences: an extension typically involves months of building work connected to your home, more disruption to daily life, and its own planning and Building Regulations process, whereas a prefabricated garden room is manufactured in our West Midlands workshop and installed on site typically over 3–5 days, without opening up the house itself. Both approaches have their place — the right one depends on the space you need and how much disruption you're willing to take on.

Running Costs to Budget For

• Electricity: heating running costs depend on insulation quality, the heater chosen, and how often the room is used — ask for guidance specific to your specification rather than a generic figure
• Council tax: garden offices and gyms typically don't attract separate council tax, but annexes used as independent living accommodation may be assessed differently — check with your council
• Insurance: most home insurance policies cover outbuildings up to a set value; confirm with your insurer and uplift cover if needed
• Maintenance: composite cladding generally needs less upkeep than timber shiplap, which will benefit from periodic treatment

Get a Real Price for Your Project

General market ranges are useful for context, but the only figure worth budgeting against is one built around your actual garden, size and specification. Use our garden room calculator to build your spec and see your price, browse the portfolio for real completed builds, or read our garden annexe cost guide if you're sizing up a full living space.