Extensions
Rear and side-return extensions
On a terrace the ground floor is usually the problem: a narrow kitchen in the back addition, a dark middle room and a side passage full of bins. We extend into the side return or across the back, and open the house up to the garden.
Five kinds of extension
Side return
We build into the passage beside the back addition, usually with a glass or part-glass roof to keep light in the middle of the house. The kitchen gets wider by two metres or so, and the old side window becomes an opening.
£68,000 TO £95,000 · 12 TO 14 WEEKS · OFTEN PLANNING PERMISSION
Rear, up to 3 m
Straight out from the back of the house, within the permitted development limits for a terrace or semi: 3 m deep, 4 m high, and no more than 3 m to the eaves within 2 m of a boundary.
£72,000 TO £98,000 · 11 TO 13 WEEKS · PERMITTED DEVELOPMENT
Rear, up to 6 m, with prior approval
A deeper single-storey extension using the larger home extension scheme. The council writes to your neighbours, who have 21 days to comment, and decides within 42 days.
£95,000 TO £135,000 · 13 TO 16 WEEKS · PRIOR APPROVAL
Wraparound
Side return and rear together, forming an L around the back addition. The biggest change you can make to a terrace's ground floor, and always a planning application.
£115,000 TO £165,000 · 15 TO 18 WEEKS · PLANNING PERMISSION
Over the back addition
A first-floor extension on top of the existing back addition, usually to make a proper family bathroom. Planning permission, and a careful conversation with the neighbours about light.
£55,000 TO £80,000 · 10 TO 12 WEEKS · PLANNING PERMISSION
Knock-throughs
Taking out the wall between the front and back rooms, or the back room and the kitchen, on a steel beam. Often done with an extension, sometimes on its own.
£9,500 to £16,000 · 2 to 3 weeks
The rules that set the size
Permitted development for single-storey extensions
On a terraced or semi-detached house you can extend up to 3 m beyond the original back wall without planning permission (4 m on a detached house), as long as the extension is no higher than 4 m, no higher than 3 m at the eaves within 2 m of a boundary, and built in materials that look like the house. Side extensions can be no wider than half the original house. Extensions and outbuildings together can't cover more than half the garden. "Original" means the house as it stood on 1 July 1948, or as built if later, so an old back addition counts as part of it and an old lean-to doesn't.
Prior approval for deeper extensions
Outside conservation areas, a terrace or semi can go to 6 m (a detached house to 8 m) through prior approval. We send the council the drawings; they notify the neighbours, who get 21 days to object; the council considers the effect on their light and privacy and has 42 days to decide. If it doesn't decide in time, the extension is approved. The council fee is £249.
Party walls and foundations
Most extensions on a terrace need at least one party wall notice: one month's notice for a new wall built on the boundary line, and one month's notice for digging foundations within 3 m of a neighbour's building and deeper than its foundations (6 m in some cases). We serve these as soon as the drawings are fixed.
Drains
Terraces often have a shared drain running under the side return or the back garden. Building over or close to a public sewer needs the water company's agreement, and we find out at the design stage with a camera survey, not when the digger finds it.
Glass and warmth
Building regulations limit the glazing in an extension to about a quarter of its floor area, plus any windows you've removed, unless a calculation shows the whole house still performs. Big glass roofs and wide sliding doors are possible; we check the numbers early so the design doesn't have to change later.
These are the national rules for England. Conservation areas, Article 4 directions and each council's own practice can change the answer, so check with your local authority, or ask us on the first call.
What's in every Quinlan extension
- Design and engineer's calculations
- Planning, prior approval or lawful development certificate, with the council fee
- Building regulations and inspections
- Party wall notices
- Drainage camera survey
- Foundations to the engineer's design
- Steelwork
- Brick to match the house (reclaimed London stock where it needs to match)
- Insulated floor with underfloor heating
- Roof with rooflights or glass as drawn
- Doors and windows
- Electrics with certificate
- Plaster and decoration in white
- Fitting of your kitchen if you want us to
- Waste removal and a final clean
- A six-month defects visit
Not included. Kitchen units and appliances, flooring, garden landscaping beyond making good, party wall surveyors' fees.
Featured project: Mattison Road, N4
FIG. 1 · Ground floor plan, existing and proposed. Drag the line, use the arrow keys, or press a button.
Mattison Road, N4 · Side-return extension · 14 weeks on site · £92,000 to £102,000
A side return for a dark galley kitchen
Glass roof on a steel frame, a knock-through and a drain we found before the digger did.
Talk to us about the ground floor
Bring your ideas, a sketch or a picture from a magazine. We'll tell you at the survey visit which route the rules allow and roughly what it costs.