A fully installed, insulated garden room costs about £15,000 to £35,000 in 2026, including VAT. A 3m by 3m room is typically about £19,700 and a 6m by 4m room about £33,600. The base, the power cable from the house, paths and any plumbing are often priced separately, and can add several thousand pounds.
Written with Risdon Renovations, a family building firm in Faversham that builds garden rooms as a whole project, from the groundwork to the planting, and has been building across Kent for over 40 years.
Garden rooms are often sold like sofas: pick a size, pick a cladding, see a price. But the room also needs a base to sit on, a trench across the lawn for the power cable, and sometimes a new fuse board in the house, which is more than any sofa has ever asked for.
One photographer on a forum priced up a kit "coming in at a tasty £3,384.99", then added, "I think I may need to increase the budget a bit..." (Talk Photography). He was right. This guide prices the room, then everything around it, so you can compare quotes that don't include the same things.
How much does a garden room cost?
A typical installed, insulated garden room costs £15,000 to £35,000 including VAT, from a survey of the published prices of 42 UK garden room companies (The Garden Room & Annexe Guide, October 2026). Size matters most. A 3m by 3m room is about £19,700, and a 6m by 4m room about £33,600.
| Size | Typical price | Per m², roughly |
|---|---|---|
| 2.5m x 2m | £15,700 | £3,140 |
| 3m x 3m | £19,700 | £2,190 |
| 4m x 3m | £22,200 | £1,850 |
| 5m x 4m | £29,800 | £1,490 |
| 6m x 4m | £33,600 | £1,400 |
Source: The Garden Room & Annexe Guide, prices checked October 2026. The per m² column is our sum.
Other guides land in the same range, which in garden room pricing is about as close as anyone gets to agreeing. Green Retreats puts a fully insulated room at £12,000 to £30,000 (Green Retreats), and quotes on MyJobQuote average £32,000 and are mostly for 12m² to 15m² rooms (MyJobQuote).
Garden room cost per m²
A garden room costs about £1,400 to £2,200 per m² for typical sizes, but small rooms cost far more per m² than big ones. Every room carries a fixed cost of about £12,400, plus about £900 for each square metre (The Garden Room & Annexe Guide). So a "£1,500 per m²" figure only fits a fairly big room.
Builder-quoted figures run higher: about £1,200 to £1,800 per m² for basic, £1,800 to £2,500 mid-range and £2,500 to £3,500 or more for high end (BookaBuilderUK). The fixed cost is the doors, the electrics and the base, which cost much the same whether the room holds a desk or a snooker table.
How much does a garden room cost to build?
What you get for the money depends on the type. A log cabin kit can cost a few thousand pounds, an insulated specialist room around £20,000 and a bespoke building £25,000 to £40,000 for the same 3m by 3m footprint. None of the 40 companies selling a 3m by 3m room prices an installed, insulated one under £10,000.
| Type | Price | What it usually includes |
|---|---|---|
| Log cabin kit | £3,600 to £5,400 | The kit. You build it, base and electrics extra |
| Installed timber cabin | about £7,000 | Built for you, thin walls, little insulation |
| Cabin with insulation, installation and base | about £11,300 | Still no electrics |
| Insulated panel kit | £8,800 to £13,000 | Warmer walls, but you or a builder assemble it |
| Specialist garden room | about £19,700 | Installed and properly insulated |
| Bespoke building | £25,000 to £40,000 | Designed for your garden and built on site |
Source: The Garden Room & Annexe Guide, October 2026.
The cheap end has a reputation, and one Reddit user put it plainly: "A log cabin style with uninsulated walls is just a glorified shed" (Reddit). It's a lovely shed in July. In January it's a very expensive fridge with a desk in it.
If the plan is deckchairs and the odd summer evening, a £3,600 log cabin kit and some patient DIY will do it, and you don't need a builder at all. I'd always rather say that up front. The gap between that kit and an installed, insulated room is about £16,000 (our sums), and it only earns its keep if you'll be out there in January.
What garden room quotes leave out
Most garden room prices cover the building, not the whole job. In one check of 20 companies, 11 included the base but only 3 included the power cable from the house (The Garden Room & Annexe Guide). Two quotes for the same size room can differ by £3,000 to £6,000 for that reason alone.
| Item | Typical figure | Source |
|---|---|---|
| Base, ground screws or fitted | £1,000 to £2,500 | Garden Room & Annexe Guide |
| Base, concrete | £3,000 to £6,500 | Garden Room & Annexe Guide |
| Power from the house, 10m to 20m run | £1,500 to £3,500 | Garden Room & Annexe Guide |
| New fuse board, if the old one can't cope | £400 to £700+ | Trade2Base |
| Data cable in the same trench | £100 to £300 | less.co.uk |
| Air conditioning, one room | £550 to £2,100 | MyJobQuote |
| Composite decking | £65 to £110 per m² | MyJobQuote |
| 8-yard skip for the spoil | £160 to £370 | MyJobQuote |
Homeowners find this out the hard way. One Mumsnet poster paid "£12,000 for the building fully installed", then "just over £1000" for the base and "£700" for the armoured cable and data (Mumsnet). So the base and the cable added just over £1,700 to a £12,000 room, and both now live under the lawn, where nobody will ever admire them.
A 4m by 3m garden room, added up
A typical 4m by 3m garden room comes to roughly £25,000 to £30,000 all in, once the base, power, data, a small deck and a skip are added. Here's every line, using the published figures above, so you can hold any quote up against it and see which lines have quietly gone missing.
| Line | Low | High |
|---|---|---|
| The room, installed and insulated | £22,200 | £22,200 |
| Base, ground screws or fitted | £1,000 | £2,500 |
| Power from the house | £1,500 | £3,500 |
| Data cable | £100 | £300 |
| Composite deck, 6m² | £390 | £660 |
| Skip | £160 | £370 |
| Total | £25,350 | £29,530 |
Our sum, using the typical 4m by 3m price and the figures in the table above. A quote that already includes the base or the power will come in lower. Heating, a path and plumbing would add more.
How much does a garden room with a toilet or shower cost?
A toilet or shower adds roughly £2,000 to £6,000 to a garden room (MyJobQuote), but there's no fair typical figure. Most of the cost is the drain run back to the house, how deep the drains are, and whether a pump is needed. A toilet also brings in building control, and sleeping in the room brings in planning.
"We generally need to dig a trench from the mains drainage of the house down to the garden room, and, depending on the length of the run and the depth of the drains we may need to install a pumping station," says Roy Wetherall of Green Retreats (Homebuilding). Jason Mennie of Haon Garden Rooms adds a warning: "be very cautious of companies that come in and don't mention those elements." Waste water only runs downhill, and it has never once cared where you wanted the shower.
Do you need planning permission or building regulations?
Often neither. A single storey garden room is usually permitted development if it's no more than 2.5m high within 2m of a boundary, and 4m with a dual-pitched roof elsewhere (3m for other roofs). It mustn't be used as a separate home. Building regulations usually don't apply under 15m², or up to 30m² with no sleeping in it and the right distance from the boundary.
| Garden room | Building regulations? |
|---|---|
| Under 15m², no one sleeps in it | Usually not needed |
| 15m² to 30m², no one sleeps in it, at least 1m from the boundary or built mostly of non-combustible material | Usually not needed |
| Over 30m², or with sleeping accommodation | Approval needed |
| The power supply from the house | Always needs certifying (Part P) |
Sources: Planning Portal and the Building Regulations 2010, regulation 9.
- Planning. The room must be single storey, sit behind the front of the house, and with other outbuildings and extensions cover no more than half the garden (GPDO Class E). Any outbuilding in the grounds of a listed building needs permission.
- National Landscapes. In the Kent Downs and the High Weald, which cover a third of Kent (Kent Downs), buildings more than 20m from the house are limited to 10m² in total.
- Conservation areas. No garden room between the side of the house and the boundary without permission. Faversham's Article 4 direction doesn't remove the right to build outbuildings (planning.data.gov.uk).
- The fee, if you need permission. £272 for an outbuilding from April 2026, not the £548 extension fee most guides quote (2026 fee schedule).
Our garden room planning permission guide goes through each rule in more detail than anyone would read for fun, and the planning permission guide for extensions covers the house itself.
Council tax, business rates and tax relief
A garden room you use as an office or a gym doesn't usually change your council tax. One built or adapted as separate living accommodation, with its own sleeping, cooking and washing facilities, must have its own council tax band (gov.uk). Business rates can apply if clients visit or staff work there (gov.uk).
The working-from-home tax relief has also gone: employees can't claim it from 6 April 2026 (gov.uk). So HMRC won't be chipping in for the desk.
Garden rooms on Kent ground
Kent ground changes the base you need. Around Faversham alone, a garden can sit on London Clay, Thanet sands, brickearth or chalk within a few miles (British Geological Survey), which makes Kent ground about as predictable as Kent weather. Clay moves with the weather to about 0.75m deep, and trees can mean foundations "need to be significantly deeper than might be first expected" (Planning Portal).
Ground screws are "great for sites with poor soil, limited access, or tree roots," says Mark Stevenson, a former managing director of Potton (Homebuilding). Protected trees are a separate matter: cutting their roots needs the council's consent, even when the room itself doesn't need planning (gov.uk). The tree was there first, and the law has taken its side.
Running costs and value
A well-insulated garden office costs about a quarter as much to heat as a thin-walled cabin, a saving of around £200 a year.
| Garden room | Heating a year |
|---|---|
| Well insulated | £65 to £95 |
| Thin-walled cabin | £260 to £320 |
Sources: The Garden Room & Annexe Guide, at Ofgem's October 2026 price cap.
Value is harder. "There is no official measure of what a garden room adds to a house price," says The Garden Room & Annexe Guide, and the 7.5% figure you'll see everywhere "is one agent's estimate, not a measure of sale prices". Build one because you'll use it, not because a headline promised you a profit.
How much does a garden office cost?
A garden office costs about £15,000 on average in 2026 (MyJobQuote), and most fall between £13,000 and £30,000 (Green Retreats). Offices are usually small, so they cost the most per m²: a one-desk room of about 2.5m by 2m is typically £15,700, or £3,140 a square metre for a commute measured in footsteps. Our garden office cost guide goes through desks, data and the tax rules.
Garden room or extension?
A garden room usually costs less per m² than an extension. A typical 5m by 4m garden room is about £29,800 including VAT (The Garden Room & Annexe Guide), while a single storey extension costs £2,200 to £3,300 per m² before VAT and fees (Homebuilding & Renovating). An extension usually adds more value, because the space is inside the house.
"As a rule, an extension will add more value because extra space in the main house is valuable to everyone," as one homeowner on Reddit put it. Risdon builds both, so our garden room vs extension guide can compare them without a favourite.
| Garden room | Extension | |
|---|---|---|
| Cost, about 20m² | about £29,800, with VAT | £44,000 to £66,000 before VAT and fees |
| Building regulations | Often not needed | Always needed |
| Value added | No official measure | Usually more, as the space is in the house |
Sources: The Garden Room & Annexe Guide for the 5m by 4m room, Homebuilding & Renovating for the extension rate (our sum for 20m²), Building Regulations 2010, Schedule 2.
What we see on Kent jobs
One thing in this guide deserves a straight face. Most garden room budgets go wrong below ground: the base, the cable run and the drains. Risdon treats a garden room as a building project, so those are priced and dug by the same team that builds the room.
- The ground first. Risdon runs its own plant, so the levels, base and drainage are dug by the people building on them.
- Power and plumbing in the same job. The cable and any pipes are run out from the house as part of the build, not left as a separate trade to find.
- The garden finished. Paths, paving and planting around the room are part of the quote, priced item by item.
- Glazing from the group. Doors and glazing come from Risdon's sister company, PGS Glass, planned with the frame rather than added afterwards.
My advice: ask every company the same three questions. Is the base included? Is the power from the house included? Who makes good the lawn?
The answers will tell you more than the brochure.
Garden room cost questions
How much does a 3m x 3m garden room cost?
A fully insulated, installed 3m by 3m garden room typically costs about £19,700 including VAT, from a survey of 42 UK companies' published prices. The base and the power cable from the house may be extra.
Is a garden room cheaper than an extension?
Usually, per square metre. A typical 5m by 4m garden room costs about £29,800 including VAT, while a single storey extension costs £2,200 to £3,300 per m² before VAT and fees. An extension usually adds more to the value of the house.
Do I need planning permission for a garden room?
Often not. A single storey garden room can be permitted development if it stays within the height limits, such as 2.5m within 2m of a boundary, and isn't used as a separate home. Listed homes, National Landscapes and conservation areas have tighter rules.
Can I put a toilet or shower in a garden room?
Yes, but plumbing is the hardest part to price, because most of the cost is the drain run back to the house and sometimes a pump. A toilet brings in building control, and using the room as a separate home needs planning permission.
Does a garden room add value to a house?
There's no official measure. The often-quoted 7.5% is one estate agent's estimate, not a study of sale prices. Build one because you'll use it, and treat any rise in value as a bonus.
William writes Risdon's guides with the team, a family building firm in Faversham that's been building across Kent for over 40 years.