Garden room vs extension: cost compared
A garden room can be a lower-cost way to create a separate office or studio. The guide’s typical garden-room budget is £16,000, while a 20 m² extension is £40,000 to £64,000 before fit-out and separate fees. Those figures are not matched-size quotes: compare the internal area, services and intended use.
Garden room vs House extension: the cost
| Option | Range | Typical | Priced |
|---|---|---|---|
| Garden room | £8,000 to £30,000 | £16,000 | installed |
| House extension | £2,000 to £3,200 | £2,500 | per m² |
Costwise guide prices, reviewed June 2026, not quotes. Note the two are quoted on different bases, so the figures above are not a like-for-like comparison on their own.
Garden room vs House extension: the difference
| Factor | How they compare |
|---|---|
| Typical cost | Garden room about £16,000 installed; extension about £2,000 to £3,200 per m² (a 20 m² build is about £40,000 to £64,000). |
| What you gain | Garden room: a separate insulated space in the garden, great for working from home. Extension: extra connected living space inside the house. |
| Planning and value | Check permission requirements for the actual use and location. Resale value needs a property-specific assessment. |
| Best for | Garden room: an affordable home office or studio. Extension: more everyday living space and added value. |
Compare a usable office of the same size
Ask for the internal dimensions and the usable desk and storage space in both designs. A garden-room product advertised by its external footprint loses area to its walls. An extension also needs circulation and a connection to the existing rooms.
A 20 m² extension is £40,000 to £64,000 at the guide’s base rate, before fit-out and separate fees. The £16,000 garden-room headline is a whole-project typical figure, not a confirmed 20 m² specification. Request a garden-room quote for the same usable office size before treating the difference as a saving.
What must the garden-room package include?
Compare delivery and assembly, base or foundations, insulation, windows and doors, electricity connection, heating, ventilation, internal finish and access to the room. A shell price without power or a prepared base is not the same as an office ready to use.
Measure the route from the street and ask who carries materials, removes spoil and repairs disturbed surfaces. A toilet or kitchenette introduces services and work beyond a simple office. Get a separate specification rather than assuming those extras are covered.
Which space fits your daily routine?
A detached room can separate work from home, but you cross the garden in bad weather and may be farther from a bathroom or kitchen. An extension connects to the house, which can suit shared family use and anyone who needs easy access.
Permission and building-control requirements depend on the use, dimensions, location and UK nation. Confirm them before ordering. Do not assume that every garden room is exempt or that estate agents will value its floor area in the same way as an extension.
Common questions
A typical garden-room budget here is £16,000, compared with £40,000 to £64,000 for a 20 m² extension build. Those figures do not assume the same internal area or services. Price the same usable room before deciding how much you would save.
A garden room and a connected extension are different types of space. Ask a local agent how the actual size, specification and approved use would be described and valued. Neither has a guaranteed return, and floor-area treatment should not be assumed from the label alone.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.