Where extending pays in Guernsey
One comparison decides whether a build is worth doing: what a square metre sells for locally against what a square metre costs to build. Guernsey new build runs £4,000–£6,000/m² by quality and refurbishment £2,000–£4,000/m². Island-wide, properties currently for sale that publish a floor area sit at a midpoint of £5,899/m² across 106 listings.
By parish: sale value per m² against build cost
| Parish | Sells for | Margin vs new build | vs mid refurb | Verdict |
|---|---|---|---|---|
| Castel (7) | £8,477/m² | +£4,477 to +£2,477 | +£5,477 | Works at any build quality |
| St Martin (10) | £6,304/m² | +£2,304 to +£304 | +£3,304 | Works at any build quality |
| St Peter Port (49) | £5,899/m² | +£1,899 to −£101 | +£2,899 | Works at mid-range build cost |
| St Pierre du Bois (5) | £5,681/m² | +£1,681 to −£319 | +£2,681 | Works at mid-range build cost |
| Vale (5) | £5,552/m² | +£1,552 to −£448 | +£2,552 | Works at mid-range build cost |
| St Sampson (11) | £5,312/m² | +£1,312 to −£688 | +£2,312 | Works at mid-range build cost |
| Sark (6) | £4,822/m² | +£822 to −£1,178 | +£1,822 | Only at basic build cost |
Margin is local value per m² minus build cost per m². The new-build column runs best case (£4,000/m²) to worst (£6,000/m²). Parishes with fewer than 5 floor-area listings are left out rather than shown on a sample that can't carry a conclusion.
On glasshouse land, a 35-per-hectare scheme breaks even at £4,205/m² in St Martin and £2,350/m² in St Sampson's, before paying anything for the land; see the idle glasshouse register.
Under-improved stock: asking well below its parish rate
Properties currently for sale asking at least 20% less per m² than the midpoint for their parish. That gap is where refurbishment or extension has the most room — though it can equally mean a small flat, a short lease, an awkward site or something structural. This is a shortlist to go and look at, not a valuation of any of them.
| Property | Asking per m² | Parish midpoint | Gap |
|---|---|---|---|
| Vivant Castel · 234.4 m² · £965,000 |
£4,117/m² | £8,477/m² | -51% |
| Sea La Vie, 13 Clos De Carteret, Route De Cart Castel · 138 m² · £695,000 |
£5,036/m² | £8,477/m² | -41% |
| Les Blanches Vinery Cottage St Martin · 374.03 m² · £1,250,000 |
£3,342/m² | £6,304/m² | -47% |
| Sark Island Stores & Bakery, The Avenue, Sark, Sark · 278.7 m² · £575,000 |
£2,063/m² | £4,822/m² | -57% |
| 45 High Street St Peter Port · 200.11 m² · £695,000 |
£3,473/m² | £5,899/m² | -41% |
| Hirondelle St Martin · 139 m² · £565,000 |
£4,065/m² | £6,304/m² | -36% |
| Valhalla St Martin · 325.1 m² · £1,395,000 |
£4,291/m² | £6,304/m² | -32% |
| Fort Road Garage St Peter Port · 144 m² · £575,000 |
£3,993/m² | £5,899/m² | -32% |
| 6 St Martins Court St Martin · 239 m² · £1,095,000 |
£4,582/m² | £6,304/m² | -27% |
| 3 Mont Bleu St Peter Port · 188 m² · £795,000 |
£4,229/m² | £5,899/m² | -28% |
| Dracena St Peter Port · 150 m² · £645,000 |
£4,300/m² | £5,899/m² | -27% |
| La Vieille Cour St Peter Port · 97.5 m² · £430,000 |
£4,410/m² | £5,899/m² | -25% |
| Apartment 7 Hanois House St Peter Port · 142 m² · £650,000 |
£4,577/m² | £5,899/m² | -22% |
| 1 Chalford St Sampson · 170 m² · £695,000 |
£4,088/m² | £5,312/m² | -23% |
Sale values here come from asking prices, because Guernsey's sold register holds no floor areas at all — so the margins reflect what sellers want, not what buyers paid. Build rates are typical Guernsey figures, not a quote, and exclude land, fees, finance and the professional team. Nothing here accounts for whether a site can physically take an extension, whether a street has a ceiling price, or the condition behind the asking price. Check what actually gets granted and who is filing successfully before committing.