Extending a Detached House: Your Options Explained
Detached houses offer the most extension flexibility — wrap-around, side, two-storey, and loft conversions are all on the table. A guide to making the most of your options.
The detached advantage
Detached houses have the most generous Permitted Development rights of any dwelling type. Single-storey rear extensions can extend up to 8m from the original rear wall (compared to 4m for semi-detached and terraced homes) under the Prior Approval process. Loft conversions can add up to 50m³ (compared to 40m³ for other types). And crucially, there are no party wall agreements — you have no shared walls. This means fewer professional fees, no neighbour negotiations, and a simpler construction process. In Dorset, detached houses are common in Canford Heath, Merley, Corfe Mullen, Upton, Lytchett Matravers, and the villages around Purbeck.
Wrap-around extensions
A wrap-around extension combines a rear and side extension into an L-shape, creating a single large ground-floor space. This is the gold standard for detached house extensions — it maximises floor area while maintaining a connection to the garden on two sides. A typical wrap-around adds 30–45m² to the ground floor, enough for a large kitchen-diner with utility room, WC, and a seating area. Cost: £55,000–£90,000 depending on size and specification. The design challenge is managing the junction between the side and rear elements — this is where roof drainage, damp-proof courses, and structural connections all converge. Get the details right here and the extension will look seamless.
Two-storey extensions
A two-storey extension is the most cost-effective way to add space because the foundations and roof serve two floors instead of one. The upper floor costs roughly 40% of the lower floor (you are adding walls, a floor, and interior finishing, but no foundations and less roof). A two-storey rear extension on a detached house typically costs £70,000–£110,000 and adds 30–50m² across two floors — often a kitchen-diner below and a master bedroom with en-suite above. Under PD, a two-storey rear extension on a detached house can project up to 3m from the original rear wall and must be at least 7m from the rear boundary. Beyond 3m, you need planning permission.
Loft conversions on detached homes
Detached houses often have the best loft conversion potential because the roof spans the full width of the house without a party wall. A rear dormer loft conversion on a detached house creates a large usable space — often 25–35m² with a proper landing, bedroom, en-suite, and storage in the eaves. If the existing roof is hipped, a hip-to-gable on both sides combined with a rear dormer creates the maximum possible floor area. Cost: £45,000–£70,000. The 50m³ volume allowance for detached houses is generous — enough for a large dormer on the rear and Velux windows on the front without exceeding PD limits. However, if the property is in a conservation area, dormers visible from the highway typically need planning permission.
Written by the PlanBuildCo team
9 years designing extensions and renovations in Poole, Dorset.
Ready to take the next step?
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