A fully insulated, professionally built garden room in the UK costs between £1,200 and £2,500 per square metre in 2026. The exact figure depends on the size of the room, the specification you choose, and what is included in the quote. Smaller rooms cost more per square metre because fixed costs like foundations, electrics, and delivery are spread across less floor area. Larger rooms bring the per-metre price down.
We have been building garden rooms across South East London, Kent, Surrey, and Sussex since 2004, and pricing is the question we get asked more than any other. This guide breaks down what you should expect to pay per square metre, how size and specification affect the numbers, and what to watch out for when comparing quotes.
Garden Room Cost Per Square Metre by Quality Tier
Not all garden rooms are built to the same standard. The market splits broadly into three quality tiers, and the price per square metre reflects the difference in materials, insulation, cladding, and glazing.
Budget tier: £1,000 to £1,500 per sqm
At this level you are looking at thinner insulation, basic cladding such as shiplap or tongue-and-groove softwood, standard double-glazed windows, and minimal internal finishing. Some companies at this price point supply flat-pack buildings for self-assembly, which keeps labour costs down but means you handle the build yourself. Foundations and electrics are often excluded.
Mid-range tier: £1,500 to £2,200 per sqm
This is where most serious garden room companies sit. You get full structural insulation (typically 100mm or more), quality timber or composite cladding, aluminium or high-grade uPVC glazing, internal plastered or lined walls, integrated electrics with consumer unit, LED lighting, and sockets. Foundations and installation are usually included. Our own builds fall into this bracket.
Premium tier: £2,200 to £3,500+ per sqm
Premium builds use materials like Western Red Cedar or larch cladding, large-format aluminium bifold or sliding doors, engineered oak flooring, bespoke joinery, and sometimes underfloor heating as standard. Companies at this end often offer architectural design services and fully bespoke layouts. If you are looking at a garden annexe with bathroom and kitchenette, you will likely land in this range too.
How Size Affects the Cost Per Square Metre
This is the part that catches most people out. A smaller garden room does not just cost less overall. It actually costs more per square metre than a larger one.
The reason is straightforward. Every garden room needs a foundation, a roof, electrical first fix, a consumer unit, delivery, and a team of builders on site. These costs do not double when you double the floor area. A 12 sqm room and a 24 sqm room need the same consumer unit, similar foundation preparation time, and the same delivery logistics. So the fixed costs get divided across more square metres in the bigger room.
Here is how that plays out in practice across our own range, using mid-range specification as a guide:
Midi (4.0m x 3.0m, roughly 12 sqm)
Total cost typically £20,000 to £28,000. That works out to roughly £1,700 to £2,300 per sqm. The smaller footprint means fixed costs have a bigger impact on the per-metre figure.
Maxi (5.0m x 3.5m, roughly 17.5 sqm)
Total cost typically £26,000 to £35,000. Per square metre, that is roughly £1,500 to £2,000. You start to see the economy of scale taking effect.
Multi (6.0m x 4.0m, roughly 24 sqm)
Total cost typically £32,000 to £44,000. Per square metre, roughly £1,350 to £1,850. This is the sweet spot for people who want a proper home office or studio with room to move.
Multi+ (7.0m x 4.5m, roughly 31.5 sqm)
Total cost typically £40,000 to £55,000. Per square metre, roughly £1,270 to £1,750. The largest footprint brings the best per-metre value, though buildings over 30 sqm may need building regulations approval, which adds some cost for compliance.
You can see our full range and current pricing on our buildings and prices page.
What Should Be Included in the Price Per Square Metre
This is where comparing garden room quotes gets tricky. Two companies can both quote £1,800 per sqm, but one includes everything and the other leaves out foundations, electrics, and VAT. Suddenly the “cheaper” quote is the more expensive build.
A genuinely turnkey garden room price should include:
- Foundations (concrete pad, screw piles, or similar)
- The full structural build including insulated walls, floor, and roof
- External cladding and weatherproof membrane
- Glazing (doors and windows)
- Internal wall and ceiling lining
- Electrical first fix and second fix (consumer unit, sockets, lighting, switches)
- Flooring
- Delivery and installation
- VAT
Common exclusions to ask about
Even with a good turnkey quote, some items are often listed separately:
- Mains electrical connection: Running a cable from your house consumer unit to the garden room. This typically costs £1,500 to £3,500 depending on the distance and whether the cable needs to cross hard landscaping or driveways.
- Site access works: If your garden has narrow side access, steep slopes, or existing structures that need removing, there may be additional site preparation costs.
- Heating: Some companies include an electric panel heater or air conditioning unit. Others treat it as an optional extra at £500 to £2,000.
- Data and internet cabling: Most people run Wi-Fi from the house, but if you want a hardwired ethernet connection, that is usually extra.
- Furniture and fit-out: Desks, shelving, and interior decoration are your own job.
When you get quotes, always ask: “Is this the total price I will pay to have a finished, usable garden room?” If the answer involves a list of extras, add those up before comparing.
Garden Room vs House Extension: Cost Per Square Metre
This comparison comes up constantly, and the numbers make a strong case for garden rooms.
A single-storey house extension in London, Kent, and Surrey currently costs between £2,000 and £3,500 per square metre, depending on the specification and the builder. In Central London, that figure can reach £4,000 to £5,000 per sqm. These prices typically exclude VAT, kitchen or bathroom fit-out, and professional fees for architects and structural engineers.
On top of the build cost, a house extension requires:
- Architectural drawings (£1,500 to £5,000)
- Structural engineer calculations (£500 to £1,500)
- Building regulations application and inspections
- Planning permission application if needed (£206 to £462)
- Party wall agreements with neighbours (£700 to £1,500 per neighbour)
- A build time of 3 to 6 months, during which your home is a building site
A garden room at £1,500 to £2,200 per sqm, with most builds completed in 1 to 3 weeks and no disruption to your home, looks very competitive by comparison. You also keep your garden room as a separate, dedicated space rather than extending the main house, which many people prefer for focused work or hobbies.
For more on our approach, take a look at our bespoke garden rooms page.
Why Cheaper Per Square Metre Is Not Always Better Value
A garden room at £1,000 per sqm that needs replacing in eight years is worse value than one at £1,800 per sqm that lasts twenty-five. The things that drive cost are usually the things that determine longevity.
Proper insulation keeps the room usable year round and reduces heating bills. Quality cladding resists weathering. Good glazing prevents condensation and heat loss. A well-designed structural frame stays true rather than warping over time.
We have seen customers come to us after a budget garden room failed within a few years. Damp getting in through inadequate membranes, floors buckling from poor ventilation design, doors that no longer close because the frame has moved. The cost to fix these problems or replace the building entirely makes the original saving meaningless.
When comparing quotes on a per-metre basis, look beyond the number. Ask about wall thickness and insulation U-values, what cladding material is being used, whether the roof is a warm roof or cold roof construction, and what guarantee comes with the build.
Using the Cost Per Square Metre as a Calculator
If you know roughly what size garden room you need, you can use the per-metre figures above as a quick garden room cost calculator.
For a mid-range, fully insulated garden room with everything included, budget at £1,500 to £2,200 per sqm as your working figure. Then multiply by your required floor area.
For example:
- A 10 sqm home office: £15,000 to £22,000
- A 15 sqm studio: £22,500 to £33,000
- A 20 sqm multi-use room: £30,000 to £44,000
- A 30 sqm large office or annexe: £45,000 to £66,000
These figures assume a standard rectangular layout on a reasonably level, accessible garden. If your site needs significant groundwork, or you want a bespoke L-shaped or curved design, add 10 to 20 percent.
For a more accurate figure based on your exact requirements, get in touch with us and we will give you a detailed quote.
What We Include in Our Pricing
At Garden Office Buildings, our prices cover everything you need for a finished, usable garden room. Foundations, full structural build, insulation, cladding, glazing, internal lining, electrics, flooring, delivery, installation, and VAT are all included. We do not play the game of advertising a low headline price and then adding extras.
We have completed over 1,000 builds since 2004 across SE London, Kent, Surrey, and Sussex. Every build is managed by our own team, not subcontracted out. You can see our full product range and pricing here.
Save £5,000 with Our Ambassador Programme
If you would like to bring the cost per square metre down further, ask us about our Ambassador Programme. Ambassadors allow us to use their completed garden room for photography and a small number of viewing visits. In return, you save £5,000 off your build price. It is a straightforward arrangement that works well for both sides.