Most single storey rear extensions in Croydon end up costing between £50,000 and £110,000 all in, but the spread is wide and the reasons for it are rarely explained properly. This guide breaks down what drives the figure on a typical Croydon house, the extras that catch people out, and how to judge whether a quote is realistic.
Builders in this part of South East London generally price a single storey rear extension at somewhere between £2,400 and £3,600 per square metre for the build itself, finished to a plastered and second fix standard. Higher specification projects with large glazed openings, structural steel and premium finishes can push past £4,000 per square metre.
Smaller extensions cost more per square metre than larger ones, because the fixed costs (foundations, a steel beam over the opening, scaffolding, skips, site set up) are spread over less floor area. Treat the figures below as realistic starting points, not quotes.
Ground conditions are the big local variable. Much of the north of the borough sits on London clay, which shrinks and swells, so foundations often need to go deeper, especially near mature trees. Deeper trenches mean more excavation, more concrete and more spoil to cart away. Further south, towards Purley, Kenley and Coulsdon, you are more likely to hit chalk and sloping plots, which bring their own costs in retaining walls and stepped levels.
Access matters more than people expect. On a mid terrace with no side passage, every barrow of soil and every bag of plaster goes through the house, which adds labour time. Glazing is the other major swing: a standard set of French doors might cost £1,500 to £3,000, while wide sliding or bifold doors can run from £5,000 to £12,000 before you add the larger steel needed above them.
Roof choice also counts. A warm flat roof with a couple of rooflights is usually the most economical. A pitched and tiled roof, or a large roof lantern, costs more but can suit the house better and may be preferred by planners in conservation areas.
A builder's price normally covers construction only. Budget a further 10 to 15 percent for professional and statutory costs, and remember that VAT at 20 percent applies to most extension work, so always ask whether a figure is quoted with or without it.
The most accurate prices come from finished building regulations drawings and a written specification, not a sketch or a planning drawing. If you ask three builders to price from a rough idea, you will get three prices for three different jobs.
Ask for an itemised breakdown showing groundworks, structure, roof, glazing, electrics, plumbing and finishes, with any provisional sums clearly marked. Be cautious of a quote far below the others: it usually means something has been left out, such as drainage alterations, making good the existing kitchen, or the steelwork.
Finally, agree a payment schedule tied to completed stages and get the start date and expected duration in writing. A straightforward single storey rear extension usually takes 10 to 14 weeks on site.
Many fall under permitted development, which allows up to 3 metres on a terraced or semi detached house and 4 metres on a detached house, or 6 and 8 metres respectively with prior approval. Flats, properties in conservation areas and homes where these rights have been removed will need a full application, so check with Croydon Council before committing to a design.
Most take 10 to 14 weeks on site, depending on size, weather and how long glazing takes to arrive. Allow a further two to four months beforehand for drawings, approvals, party wall matters and any Thames Water agreement.
It depends on the street and the ceiling price for houses nearby. A well designed kitchen extension usually adds meaningful value in Croydon, but it will not always exceed the build cost, so it is worth asking a local estate agent what comparable extended homes have sold for.