What is an extension or loft worth in Guernsey?
These are works to a house
Extensions, lofts, garage conversions and annexes assume a property you can build on or into — a house, bungalow or cottage with its own footprint. None of them applies to a flat or an apartment, where the floor area is fixed and the fabric is shared. The £/m² basis below is the whole island's stock, flats included.
Space in Guernsey is asking about £5,622 per m² (46 listings publish a floor area). Build costs below are published per-m² ranges with a 25% island premium. Neither is a quote, and value added is never the whole story — the first extension on a small house adds more than the third on a large one.
| Work | Size assumed | Likely build cost | Value that space would ask | Difference | Granted |
|---|---|---|---|---|---|
| Demolish and rebuild | 140 m² | £490,000 | £787,080 | +£297,080 | 89% 296 decided |
| Two-storey extension | 45 m² | £123,750 | £252,990 | +£129,240 | 89% 28 decided |
| Single-storey extension | 25 m² | £75,000 | £140,550 | +£65,550 | 94% 835 decided |
| Loft conversion converted space, valued at 85% of the local rate |
22 m² | £48,125 | £105,131 | +£57,006 | — |
| Annexe or outbuilding converted space, valued at 75% of the local rate |
30 m² | £78,750 | £126,495 | +£47,745 | — |
| Garage conversion converted space, valued at 70% of the local rate |
16 m² | £25,000 | £62,966 | +£37,966 | — |
What this is doing, exactly
- Value is the local asking rate per m² multiplied by the space added — discounted for conversions, where a converted garage or loft does not fetch what new build does.
- Cost is a published per-m² range for that kind of work, adjusted for Guernsey. It excludes professional fees, planning fees, VAT or GST, and anything the drawings show that the description does not.
- Granted is this island's own record for that kind of application — 3,176 decided applications. It is not a prediction about yours.
- A positive difference is not a profit. It ignores the cost of money, the months of disruption, and the fact that a buyer pays for a house, not a spreadsheet.