Rear, side, two-storey, hip to gable loft and garage: what suits, what it costs
A 1930s semi usually has cavity walls, a hipped roof, a garage or side gap and a long back garden. That suits five projects: a rear extension (from £62,000), a loft conversion with a hip to gable (from £45,000), a side or wraparound extension (from £40,000), a two-storey extension (from £100,000) and a garage conversion (from £18,000). All guide prices from our calculator, plus VAT.
| Your project | Usually | The rule |
|---|---|---|
| Rear extension | The usual first project | Opens the back of the house to the garden, often with a kitchen-diner. Price from £62,000. |
| Loft conversion | Hip to gable or dormer | The hipped roof is built out to a gable (a vertical side wall) to make a full-height room. Price from £45,000. |
| Side extension | Uses the side gap | Single storey along the side, or two storeys with the first floor set back. Price from £40,000 for a single-storey side. |
| Wraparound | Side and rear together | A side and a rear extension in one, for a large open ground floor. Price from £120,000. |
| Two-storey extension | Rooms above and below | Adds a ground-floor room and a bedroom over it. Price from £100,000. |
| Garage conversion | Turn the garage into a room | Fills the garage door with wall and window, then insulates and heats it. Price from £18,000. |
| Type and size | Roughly | Guide price, plus VAT | Per m² | Calculator |
|---|---|---|---|---|
| Rear extensionSmall | 3m depth (~12m²) | £62,000 – £85,000 | £4,450 – £8,500 per m² | Price it → |
| Rear extensionMedium | 4-5m depth (~20m²) | £88,000 – £120,000 | £3,650 – £6,650 per m² | Price it → |
| Rear extensionLarge | 6m+ depth (~30m²+) | £122,000 – £165,000 | £3,200 – £5,900 per m² | Price it → |
 Side extension (single storey)Small | 1-2m width (~6-10m²) | £40,000 – £75,000 | £4,000 – £12,500 per m² | Price it → |
| Side extension (single storey)Medium | 2-3m width (~12-18m²) | £55,000 – £90,000 | £3,050 – £7,500 per m² | Price it → |
| Side extension (single storey)Large | 3m+ width (~20m²+) | £75,000 – £120,000 | £2,700 – £6,000 per m² | Price it → |
 Two-storey extensionSmall | 3m depth (~24m² total) | £100,000 – £140,000 | £3,550 – £7,000 per m² | Price it → |
| Two-storey extensionMedium | 4-5m depth (~36m² total) | £140,000 – £190,000 | £3,200 – £5,950 per m² | Price it → |
| Two-storey extensionLarge | 6m+ depth (~50m²+ total) | £190,000 – £260,000 | £2,950 – £5,400 per m² | Price it → |
 Loft dormerBedroom Only | 1 room (~18-22m²) | £45,000 – £60,000 | £2,050 – £3,350 per m² | Price it → |
| Loft dormerBedroom + En-suite | 1 room + bathroom (~22-28m²) | £75,000 – £110,000 | £2,700 – £5,000 per m² | Price it → |
| Loft dormerFull Loft | 2 rooms + bathroom (~30-40m²) | £125,000 – £160,000 | £3,100 – £5,350 per m² | Price it → |
 Garage conversionSingle Garage | One room (~12–15m²) | £18,000 – £30,000 | £1,200 – £2,500 per m² | Price it → |
| Garage conversionSingle + Structural | With alterations (~15–20m²) | £35,000 – £60,000 | £1,750 – £4,000 per m² | Price it → |
| Garage conversionDouble Garage | Larger conversion (~25–35m²) | £50,000 – £75,000 | £1,450 – £3,000 per m² | Price it → |
The same figures as our cost calculator, for the building work at a mid-range finish. They are guide prices while our launch pricing is finalised; your exact price follows a free survey. Per m² is the guide price divided by the size, rounded.
For more detail, read our extension cost guide and loft cost guide.
Most 1930s semis have two skins of brick with a gap between, which is easier to open up than a Victorian solid wall. Steels are still needed over a wide opening, and the engineer designs them.
The roof slopes at the side as well as the front and back. A hip to gable loft builds the side up to a gable wall. It counts towards the 50 m³ limit for roof extensions on a semi.
Many councils want a first-floor side extension set back from the front and kept away from the boundary, so the pair of semis does not join to the next house. We check the council's rule early.
Matching the front matters most: brick, render, pebble-dash and tiles. The materials rule for permitted development asks for a similar look.
A semi shares one wall with a neighbour. Cutting in beams, or building against it, usually needs a party wall agreement with that neighbour. See our party wall guide.
Converting it needs insulation, damp-proofing, a new floor build-up and Building Regulations approval, even when no planning is needed.
A rear dormer is often permitted development: up to 50 m³ of extra roof space on a semi or detached house, not facing the street. Usually no planning application when the work is inside and the garage door becomes wall and window, unless the house's permitted development rights have been removed. Usually needs a planning application in London: permitted development only covers two storeys up to 3 m deep and at least 7 m from the back boundary. See our planning guides for extensions and lofts.
The same figures as our cost calculator, for the building work at a mid-range finish. They are guide prices while our launch pricing is finalised; your exact price follows a free survey. General guidance, not legal advice.
Rear extension & full refurbishment
Opening up the back of the house to the garden: a rear extension and full interior refurbishment that turned a standard layout into an expansive, light-filled family space.
Rear & loft extension, full refurbishment
A coordinated rear, side and loft extension with a full interior refurbishment, extending on three fronts to unlock the whole property.
Rear & loft extension, full refurbishment
A rear and loft extension that overhauled the scale of a terrace home, extending out and up while modernising the whole interior.
A 1930s semi usually has cavity walls, a hipped roof, a garage or side gap and a long back garden. That suits five projects: a rear extension (from £62,000), a loft conversion with a hip to gable (from £45,000), a side or wraparound extension (from £40,000), a two-storey extension (from £100,000) and a garage conversion (from £18,000). All guide prices from our calculator, plus VAT.
A rear extension starts from £62,000, a wraparound from £120,000 and a two-storey extension from £100,000, plus VAT. The size decides the rest.
On a hipped roof the side slopes inwards. A hip to gable conversion builds that side up into a vertical gable wall, which gives room for a full-height bedroom and stairs. It is common on 1930s semis.
A rear dormer is often permitted development: up to 50 m³ of extra roof space on a semi or detached house, not facing the street. Guidance for homes in England, not advice. A conservation area, a listed building or an Article 4 direction changes the rules, and we confirm what applies on survey.
Usually no planning application when the work is inside and the garage door becomes wall and window, unless the house's permitted development rights have been removed. It still needs Building Regulations approval.
Usually, yes. A semi shares a wall with one neighbour, and cutting in beams or building against it normally needs an agreement. We explain it on the survey.
Book a free survey. We come and look at the house, then give you a written price. No charge, no obligation.
