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 £6,271/m² across 120 listings.
By parish: sale value per m² against build cost
| Parish | Sells for | Margin vs new build | vs mid refurb | Verdict |
|---|---|---|---|---|
| Castel (8) | £8,475/m² | +£4,475 to +£2,475 | +£5,475 | Works at any build quality |
| St Martin (13) | £7,396/m² | +£3,396 to +£1,396 | +£4,396 | Works at any build quality |
| St Peter's (5) | £6,313/m² | +£2,313 to +£313 | +£3,313 | Works at any build quality |
| St Sampson (10) | £6,271/m² | +£2,271 to +£271 | +£3,271 | Works at any build quality |
| St Peter Port (58) | £6,093/m² | +£2,093 to +£93 | +£3,093 | Works at any build quality |
| Vale (7) | £5,208/m² | +£1,208 to −£792 | +£2,208 | 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.
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 | £8,475/m² | -51% |
| Les Blanches Vinery Cottage St Martin · 374 m² · £1,250,000 |
£3,342/m² | £7,396/m² | -55% |
| La Soufleuresse Castel · 273 m² · £1,250,000 |
£4,579/m² | £8,475/m² | -46% |
| Sea La Vie, 13 Clos De Carteret, Route De Cart Castel · 138 m² · £695,000 |
£5,036/m² | £8,475/m² | -41% |
| Hirondelle St Martin · 139 m² · £565,000 |
£4,065/m² | £7,396/m² | -45% |
| Valhalla St Martin · 325.1 m² · £1,395,000 |
£4,291/m² | £7,396/m² | -42% |
| 6 St Martins Court St Martin · 239 m² · £1,095,000 |
£4,582/m² | £7,396/m² | -38% |
| Sark Island Stores & Bakery, The Avenue, Sark, Sark · 278.7 m² · £575,000 |
£2,063/m² | £4,822/m² | -57% |
| Campbell Lodge St Peter Port · 264 m² · £995,000 |
£3,769/m² | £6,093/m² | -38% |
| Elkington Villa St Peter Port · 228 m² · £875,000 |
£3,838/m² | £6,093/m² | -37% |
| Fort Road Garage St Peter Port · 144 m² · £575,000 |
£3,993/m² | £6,093/m² | -34% |
| 3 Mont Bleu St Peter Port · 188 m² · £795,000 |
£4,229/m² | £6,093/m² | -31% |
| La Vieille Cour St Peter Port · 97.5 m² · £430,000 |
£4,410/m² | £6,093/m² | -28% |
| Les Loumaies St Peter's · 212 m² · £995,000 |
£4,693/m² | £6,313/m² | -26% |
| Lowry St Peter Port · 186 m² · £849,000 |
£4,565/m² | £6,093/m² | -25% |
| Apartment 7 Hanois House St Peter Port · 142 m² · £650,000 |
£4,577/m² | £6,093/m² | -25% |
| La Neuve Chaumiere St Sampson · 206.1 m² · £985,000 |
£4,779/m² | £6,271/m² | -24% |
| Apartment 10 Panorama House St Peter Port · 106 m² · £495,000 |
£4,670/m² | £6,093/m² | -23% |
| Roseneath, The Grange, St Peter Port St Peter Port · 389.81 m² · £1,850,000 |
£4,746/m² | £6,093/m² | -22% |
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.