Loft conversion vs extension: which is cheaper?
For a similar amount of extra space, a loft conversion (typically £45,000) is usually cheaper than a single-storey extension and costs you no garden. A 20 m² extension is roughly £40,000 to £64,000 for the build before a kitchen fit-out. A loft adds upstairs bedroom space; an extension adds ground-floor living space, so the better value depends on the room you actually need.
Loft conversion vs House extension: the cost
| Option | Range | Typical | Priced |
|---|---|---|---|
| Loft conversion | £22,000 to £75,000 | £45,000 | for the project |
| 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.
Loft conversion vs House extension: the difference
| Factor | How they compare |
|---|---|
| Typical cost | Loft conversion about £45,000 for the project; single-storey extension about £2,000 to £3,200 per m² (so a 20 m² build is about £40,000 to £64,000). |
| Space gained | Loft: a bedroom, often with an en-suite, upstairs. Extension: ground-floor living space such as a kitchen or family room. |
| Garden | A loft conversion keeps your garden; a ground-floor extension takes some of it. |
| Best for | Loft: an extra bedroom at lower cost without losing outdoor space. Extension: bigger ground-floor living or kitchen space. |
Common questions
Usually yes for the equivalent space. A typical loft conversion is around £45,000, while a single-storey extension large enough to add a comparable room often costs more once you include the kitchen or bathroom fit-out.
Both can add value. A loft that adds a double bedroom and en-suite often returns well, while a kitchen extension can transform how a home feels. It depends on your property and area, and is never guaranteed.
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.