Garden Room Cost UK 2026: Prices by Size, Spec and Extras
What a garden room or garden office really costs in 2026, by size and specification, with a component breakdown, the extras that add up, running costs, the permitted development rules and a worked Southampton example.
Key takeaways
- A 3 m x 3 m insulated garden room typically costs £15,000 to £25,000 installed in 2026.
- Expect £1,200 to £2,500 per m² for a turnkey room, with small rooms dearer per m².
- Most garden rooms are permitted development if kept under 2.5 m high within 2 m of a boundary and used incidentally to the house, not as a self-contained annexe.
- Adding a shower and toilet typically takes a 5 m x 3 m room to £25,500 to £45,000, or up to about £47,500 with a pumped drain.
On this page (25 sections)
- Garden room cost at a glance
- Garden room sizes and a quick cost calculator
- Garden room prices by specification
- Garden office cost
- Cost breakdown by component
- Extras that add cost
- Running costs and insulation
- Garden room planning permission
- Building regulations for garden rooms
- Timber frame vs SIPs vs modular
- Does a garden room add value?
- How long does it take?
- Worked example: a 4 m x 3 m garden office in Southampton
- How to get accurate quotes
- Garden rooms in Southampton
- Garden room vs extension vs loft vs conservatory
- Base options compared
- Cladding options and costs
- Roof options
- Heating and cooling
- Plumbing a garden room
- Insurance, council tax and mortgages
- Common mistakes
- Maintenance
- Garden annexe cost and planning
A garden room in the UK typically costs £15,000 to £25,000 for a 3 m x 3 m insulated room in 2026, supplied and installed, and £28,000 to £45,000 for a 5 m x 4 m room. Per square metre, expect £1,200 to £2,500, with most people spending £20,000 to £35,000 in total.
This guide breaks the price down by size and specification, itemises every component, lists the extras that push quotes up, covers running costs, the permitted development and building regulations rules, and ends with a worked example for a garden office in Southampton. Figures are based on published UK trade cost guides, adjusted for south Hampshire rates. They include VAT unless stated, because most garden room suppliers quote that way.
Garden room cost at a glance
Garden room cost by size (2026, installed)
| Size | Floor area | Typical installed cost (2026) |
|---|---|---|
| 3 m x 3 m | 9 m² | £15,000 – £25,000 |
| 4 m x 3 m | 12 m² | £18,000 – £30,000 |
| 5 m x 3 m | 15 m² | £22,000 – £35,000 |
| 5 m x 4 m | 20 m² | £28,000 – £45,000 |
| 6 m x 4 m | 24 m² | £32,000 – £55,000 |
Per square metre, an insulated, turnkey garden room costs £1,200 to £2,500 installed, with the fixed costs of base, electrics and doors making small rooms dearer per m² than large ones. The national average for a 3 by 3 metre room is a little over £21,000. Costs in London and the South East, including Hampshire, run 10 to 25 per cent above the national figures.
Garden room sizes and a quick cost calculator
The most common garden room sizes are 3 by 3 metres (a home office for one), 4 by 3 metres (an office with a sofa or a small gym), 5 by 3 metres (office plus guest space or a hobby room) and 5 by 4 metres or larger (a family room, studio or annexe). Keep under 2.5 metres high within 2 metres of a boundary if you want to stay inside permitted development, which caps most rooms at a flat or very shallow roof.
For a quick estimate, work it out in three steps:
- Floor area x rate. Multiply the floor area by £1,200 per m² for a basic insulated room, £1,800 for a mid-range room or £2,500 for a high-specification one.
- Add the fixed costs. Add £1,500 to £4,000 for the base and £1,000 to £3,500 for the electrical supply, depending on the distance from the house.
- Add the extras. Add a shower room (see below), air-conditioning (£1,500 to £3,000) or upgraded doors as needed.
A 4 by 3 metre mid-range garden office works out at roughly 12 x £1,800 = £21,600, plus £2,500 for the base and £2,000 for electrics: about £26,000 installed. Treat the result as a budget to test quotes against, not a price.
Garden room prices by specification
| Tier | Typical cost, 12 m² | What you get |
|---|---|---|
| Basic shell or summerhouse | £8,000 – £15,000 | Timber frame, single glazing or basic double, minimal insulation, felt or EPDM roof, no electrics |
| Mid-range insulated | £15,000 – £25,000 | Fully insulated floor, walls and roof, double-glazed aluminium or uPVC doors, EPDM roof, electrics, lined and decorated |
| High specification | £25,000 – £40,000+ | SIPs or thick timber frame, bifold or slimline sliding doors, cedar or composite cladding, LED lighting, air-con or underfloor heating, plumbing for a WC or shower |
Three ways to buy: a kit you assemble yourself (cheapest, most work), a shell built by a supplier that you fit out, or turnkey where everything from base to decoration is done. The tables above are turnkey.
Garden office cost
A garden office is a mid-range insulated room with three additions: data cabling or a wired network point, more sockets and lighting than a studio, and heating or cooling for year-round use. Budget £18,000 to £30,000 for a 12 m² office with a desk wall, built-in storage and a small air-conditioning unit, and add £2,000 to £6,000 for a WC and basin if the drain run allows.
Cost breakdown by component
The structure is the biggest line at £4,000 to £9,000 for a timber frame or £6,000 to £12,000 for SIPs, followed by windows and doors at £2,000 to £8,000.
| Component | Typical cost | Notes |
|---|---|---|
| Base: concrete slab | £1,500 – £4,000 | Depends on size and ground |
| Base: ground screws | £1,500 – £3,000 | Faster, less mess, suits sloping gardens |
| Structure: timber frame | £4,000 – £9,000 | Most common; insulated between studs |
| Structure: SIPs panels | £6,000 – £12,000 | Better insulation, faster on site |
| Cladding | £1,500 – £5,000 | Softwood, cedar, larch, composite |
| Roof: EPDM rubber | £1,000 – £2,500 | Standard flat roof covering |
| Windows and doors | £2,000 – £8,000 | Standard double glazing to slimline bifolds |
| Insulation (floor, walls, roof) | £1,500 – £4,000 | PIR or mineral wool |
| Electrics, incl. supply cable | £1,100 – £3,000 | Circuit, sockets, lights, Part P certificate |
| Internal lining and decoration | £1,000 – £3,000 | Plasterboard skimmed, or timber lining |
| Flooring | £500 – £1,500 | Laminate, LVT, engineered timber |
| Heating or cooling | £300 – £2,500 | Panel heater to air-con unit |
| Decking or path | £500 – £3,000 | Optional |
At £250 to £350 per person per day for a two-person team over one to three weeks, labour is roughly £2,500 to £10,500 of the total.
Extras that add cost
The biggest extras are a bathroom or kitchenette at £2,000 to £6,000 plus the drain connection, and bifold or slimline sliding doors at £2,000 to £6,000 over standard doors.
- Bathroom or kitchenette: £2,000 to £6,000 plus the drain connection, which is the hard part on most gardens
- Bifold or slimline sliding doors: £2,000 to £6,000 over standard doors
- Roof lights: £800 to £2,000 each
- Drainage and soakaway: £500 to £2,000
- Trenching for the electrical supply: £300 to £1,000, more across paving
- Consumer unit upgrade if the house board has no spare way: £400 to £900
- Difficult access: hand-carried materials or a crane add hundreds to thousands
- Sloping ground: a stepped base or ground screws
- Decking, steps and lighting outside
Running costs and insulation
An insulated 12 m² room used as an office costs roughly £30 to £70 a month in winter for heating and lighting, depending on tariff and hours. What decides it is the specification: at least 100 mm of PIR in the floor and roof and 75 to 100 mm in the walls, double-glazed doors with a U-value around 1.4 W/m²K or better, and a draught-free build. An uninsulated summerhouse costs far more to heat and never gets comfortable.
Garden room planning permission
Most garden rooms need no planning permission because they are permitted development under Class E (outbuildings), provided that:
- The room is single storey with eaves no higher than 2.5 metres, and an overall height of no more than 2.5 metres if any part is within 2 metres of a boundary; otherwise 4 metres for a dual-pitched roof or 3 metres for any other roof
- It does not sit forward of the principal elevation of the house
- Outbuildings, extensions and other structures together cover no more than half the land around the original house
- There are no balconies, verandas or raised platforms over 300 mm
- The use is incidental to the house: office, gym, studio, playroom, occasional guests. A self-contained annexe someone lives in is not, and needs planning permission
The rules are tighter on designated land (conservation areas, national parks, AONBs), where an outbuilding to the side of the house is not permitted, and listed buildings need consent for any outbuilding. Many newer estates have permitted development rights removed by planning condition, so check the original decision notice. Our planning permission guide explains the wider rules; the Planning Portal is the authoritative source.
Building regulations for garden rooms
A garden room under 15 m², or under 30 m² and at least 1 metre from a boundary, with no sleeping accommodation is exempt from building regulations, though a new circuit still needs Part P certification. Building regulations are separate from planning:
- Under 15 m² with no sleeping accommodation: exempt
- 15 to 30 m² with no sleeping accommodation: exempt if at least 1 metre from a boundary, or built of substantially non-combustible materials
- Over 30 m², or any room with sleeping accommodation: full building regulations apply
- Electrics: a new circuit must be installed and certified under Part P whatever the size
- Drainage: a WC or basin connected to the foul drain needs building control approval
Timber frame vs SIPs vs modular
Timber frame is the standard: flexible, well understood, insulated between the studs, and the cheapest way to a good room. SIPs (structural insulated panels) are factory-made panels with insulation bonded in, faster on site and thermally better, at a premium. Modular or prefabricated rooms arrive largely built and are craned or carried in; quick and consistent, but access and design flexibility are the limits. For most gardens, a well-built timber frame or SIPs room from a local builder gives the best value.
Does a garden room add value?
A well-built, insulated garden room typically adds 5 to 10 per cent to a home's value, and it sells houses: a usable home office appeals to many buyers. A cheap shed-style room adds little and a poorly sited one can detract. The return is best when the room is clearly a year-round space with power, heating and good glazing, and when it does not swallow the whole garden.
How long does it take?
Lead times from order run six to twelve weeks for a supplier-built room; on site, a base takes a few days and the build one to three weeks depending on size and specification. A bespoke room from a builder follows the same pattern, with design and any planning check at the front.
Worked example: a 4 m x 3 m garden office in Southampton
Illustrative example. A 12 m² insulated garden office on a level lawn in Hedge End would cost roughly: ground screws £2,000; timber frame with 100 mm PIR insulation £6,500; cedar cladding £3,000; EPDM roof £1,500; aluminium double-glazed sliding doors and one window £4,000; plasterboard lining, skim and decoration £2,000; LVT flooring £700; electrics with armoured supply, trench, sockets, LED lighting and data point £2,400; air-conditioning unit for heating and cooling £1,500; small deck and step £1,200. Total around £24,800 including VAT, four days for the base and eleven days for the build.
How to get accurate quotes
Ask for the specification in writing: insulation thickness in floor, walls and roof; glazing U-value; roof covering and its guarantee; cladding species and treatment; whether the base, electrics and Part P certificate are included; and the deposit terms, which should not exceed 25 to 30 per cent, and never more than half. Check the installer's insurance and ask for a structural and weatherproofing guarantee of ten years. Then compare like with like, because a £12,000 room and a £24,000 room can look identical in a photograph.
Garden rooms in Southampton
Garden rooms, home offices, gyms and annexes are part of our new builds and outbuildings service across Southampton, Totton, Fair Oak, Whiteley and the surrounding area, from around £15,000 for an insulated room. Because we are a renovation company rather than a kit supplier, the base, structure, electrics, plumbing and finishes are all done by one team, and where a room needs planning permission or building regulations approval, we handle it.
Garden room vs extension vs loft vs conservatory
| Option | Typical cost (2026) | Planning | Best for | Drawbacks |
|---|---|---|---|---|
| Garden room, insulated | £15,000 – £35,000 | Usually permitted development | Office, studio, gym, guest space | Not connected to the house; walk across the garden |
| Single-storey extension | £72,000 – £156,000 (Southampton, inc VAT) | Often PD; building regs always | Kitchen-diner, living space | Cost, disruption, garden lost |
| Loft conversion | £30,000 – £84,000+ (south Hampshire, inc VAT) | Often PD; building regs always | Bedroom and en-suite | Head height, stairs, not a ground-floor space |
| Conservatory | £10,000 – £30,000 | Usually PD | Sunroom | Hot in summer, cold in winter unless glazed to a high spec |
A garden room is the cheapest way to add a usable, separate room, and separation is exactly what a home office needs. If the aim is a bigger kitchen or a bedroom, the other options win.
Base options compared
| Base | Cost, 12 m² | Pros | Cons |
|---|---|---|---|
| Concrete slab | £1,500 – £4,000 | Solid, permanent, suits heavy rooms | Excavation, mess, drying time, hard to remove |
| Ground screws | £1,500 – £3,000 | Fast, no excavation, suits slopes and tree roots | Needs a suspended floor; less suited to very heavy structures |
| Concrete pads and beams | £1,000 – £2,500 | Cheaper, less concrete | More design effort; suspended floor |
| Timber frame on pads | £800 – £2,000 | Cheapest | Lifespan depends on timber treatment and ventilation |
Ground screws have become the default for most suppliers because a crew can install them in a morning and build the next day.
Cladding options and costs
| Cladding | Cost per m² supplied and fitted | Character and maintenance |
|---|---|---|
| Treated softwood | £40 – £70 | Budget; needs staining every few years |
| Thermowood | £60 – £90 | Stable, silvers naturally, low maintenance |
| Western red cedar | £80 – £130 | Classic garden-room look, silvers to grey, minimal maintenance |
| Larch | £70 – £110 | Hard-wearing, silvers, minimal maintenance |
| Composite | £90 – £150 | No maintenance, consistent colour, fire-rated options |
| Render or fibre-cement board | £70 – £120 | Matches a rendered house; painted finish |
Brick garden room cost
A brick or block-built garden room is a small single-storey building rather than a timber room on a base, so it is priced like one: roughly £1,800 to £3,000 per m², or about £24,000 to £40,000 for a 4 by 3 metre room. It takes longer to build, needs proper foundations and is more likely to need building regulations approval, but it lasts as long as the house, matches existing brickwork and is easier to use as an annexe later.
Roof options
A flat roof with EPDM rubber is the standard: cheap, twenty-year plus lifespan, and it keeps the height under the 2.5 metre limit near boundaries. GRP fibreglass is a step up in durability at a small premium. A green roof with sedum adds £60 to £100 per m² and looks superb from upstairs windows. A pitched roof with tiles or metal suits a room away from boundaries where the 4 metre dual-pitch allowance applies, and gives a vaulted ceiling inside. Roof lights in a flat roof transform the light in a deep room.
Heating and cooling
An electric panel heater at £100 to £300 is the budget option and fine for occasional use. An air-conditioning unit on heat mode at £1,200 to £2,500 installed is the best all-round answer for a daily office: efficient heating in winter and cooling in summer, when a glazed garden room can overheat. Electric underfloor heating at £600 to £1,200 is invisible and comfortable but slower to respond. Connecting to the house's wet central heating is rarely worth the trench and the heat loss.
Plumbing a garden room
A WC, basin or shower adds £2,000 to £6,000 plus the drainage. The hard part is the drain: gravity to the house's foul drain needs a fall along the run, which on a long garden may not exist, in which case a small pumped station adds £1,000 to £2,500. Water supply needs an insulated buried pipe. Plumbing turns an exempt outbuilding into one that needs building control approval for the drainage, and a room with a bathroom, kitchen and bed is an annexe that needs planning permission.
Cost of a garden room with a shower and toilet
Putting the pieces together, a 5 by 3 metre garden room with a small shower room (shower, WC and basin) typically costs £25,500 to £45,000 installed in 2026: the room itself at £22,000 to £35,000, the fittings and tiling at £2,000 to £6,000, and the water supply, drainage and building control at £1,500 to £4,000, plus £1,000 to £2,500 more if the drain needs a pump. A shower room needs an extractor fan, a waterproofed (tanked) floor and walls, and enough insulation to stop condensation, so it is not the place to save on the budget build.
Insurance, council tax and mortgages
Tell your home insurer about the garden room; most add it to the buildings cover for a small premium, and a room with valuable equipment in it needs contents cover that extends to outbuildings. A garden room used as an office does not attract business rates or separate council tax as long as it is incidental to the house and not a self-contained dwelling. Lenders take no interest in an outbuilding under permitted development, but a self-contained annexe can complicate a remortgage.
Common mistakes
- Buying on the photograph without reading the insulation specification
- Siting the room where it takes the whole lawn or the afternoon sun from the house
- Forgetting the trench for the power cable in the budget
- Exceeding 2.5 metres near a boundary with a pitched roof
- A felt roof instead of EPDM or GRP
- No ventilation, so the room is stuffy in summer and damp in winter
- Sleeping in it and calling it incidental
- Paying more than half the cost up front
Maintenance
A well-built garden room needs very little: clear the gutters and the roof outlet each autumn, check the silicone around doors and windows every couple of years, re-oil or stain softwood cladding on its schedule, leave cedar and larch to silver, and keep vegetation off the cladding and away from the base so the air can move. Twenty-five years is a reasonable expectation for a quality room.
Garden annexe cost and planning
A garden annexe is different from a garden room: it is somewhere a person lives, with a bedroom, bathroom and kitchen, typically for an elderly parent or an adult child. It is not incidental to the house, so it needs planning permission as ancillary accommodation, usually with a condition tying it to the main house so it cannot be sold separately. Build cost runs £40,000 to £90,000 for a well-insulated one-bedroom annexe with full plumbing and heating, and it must meet full building regulations because it contains sleeping accommodation. Council tax treatment depends on whether the council decides it is a separate dwelling; an annexe occupied by a dependent relative can qualify for a discount or exemption. Plan the drainage, access and privacy from the start, and talk to the planning department before spending money on drawings.
Planning a garden room or office?
A free site visit, a check on the planning and building regulations position, and a detailed written quote for a room built to last. VAT stated clearly.
Garden rooms are a cost-effective way to add usable space to a home, provided you buy an insulated, properly built one. Figures in this guide are correct as of August 2026.
Written by
The Pure Renovation & Design team
A Southampton design-and-build company whose team has 18 years of hands-on experience in extensions, loft conversions, full renovations, bathrooms and joinery across Hampshire. Prices are cross-checked against published UK trade cost guides and official fee schedules, and reviewed whenever prices or rules change.
Last reviewed 13 October 2026 · About the team
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