Part single, part two-storey extensions in Streatham

Useful details for planning a part single, part two-storey extension in Streatham.

Postcode districts: SW16
County / area: Greater London, England
Price region: London
Guide price: £86,500–£119,000 (£2,400–£3,300 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Furzedown (0.7 miles), Norbury (1.1 miles), Tooting (1.4 miles)
First visit: Free, no obligation

About a part single, part two-storey extension

A part single, part two-storey extension is an extension where the ground floor is wider or deeper than the floor above, so only part of it rises to two storeys. It usually gives a large kitchen or living area with roof lights below and one bedroom or bathroom above. It is often a good way to add space while limiting the effect on neighbours.

We cover Streatham (SW16) and the places around it, including Furzedown (0.7 miles), Norbury (1.1 miles) and Tooting.

What it costs in Streatham

Our guide for London is £2,400–£3,300 per m² including VAT. On a project with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total), that puts a part single, part two-storey extension in Streatham at roughly £86,500–£119,000. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	A 6 m × 4 m ground floor and a first floor over half of it (36 m² in total)
Essential	£2,210–£3,040 per m²	£79,500–£109,500
Standard	£2,400–£3,300 per m²	£86,500–£119,000
Premium	£2,880–£3,960 per m²	£103,500–£142,500

Planning and building regulations in Streatham

In England, the extension can only be permitted development if it goes no more than 3 m beyond the original rear wall and stays at least 7 m from the rear boundary, with matching materials and roof pitch. We check the whole design against the rules, including the 50% garden coverage limit. If any part fails, or extends beyond a side wall on two floors, you need planning permission, costing £548 (or £575 for applications made from 8 December 2026).

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

Design points for Streatham homes

Where to put the two-storey part

The two-storey section usually works best away from the closest neighbour, with the single-storey part on that boundary side. We test a few positions against neighbours' windows, the upstairs layout and the roof shape before choosing the one to take forward.

The roof junction

Where the single-storey roof meets the two-storey wall you need a sound weathering detail, usually a lead or similar flashing, and enough height for roof lights or a lantern. We set the roof falls and the upstairs window sill heights together so they do not clash.

How we'd run your project

Look at the house
We start in Streatham with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Questions about part single, part two-storey extensions in Streatham

Do I need planning permission for a part single, part two-storey extension in Streatham?

Streatham is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

How much does a part single, part two-storey extension cost in Streatham?

Our guide for London, which covers Streatham, is £2,400–£3,300 per m² including VAT. A typical project with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total) comes to about £86,500–£119,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Which postcodes do you cover around Streatham?

We cover Streatham (SW16) and nearby places including Furzedown, Norbury and Tooting, plus the rest of Greater London. The first site visit is free.

Which side should the two-storey part go on?

Usually the side furthest from the nearest neighbour's windows, so the single-storey part sits nearest them and keeps their light. Other factors are where the stairs land upstairs, which room needs the extra space and where drains run. We sketch options at the design stage and explain which is most likely to be approved.

Can the single-storey part be deeper than the two-storey part?

With planning permission, yes, and that is often the point of the design: the ground floor projects further into the garden while the first floor stays back from neighbours. Under permitted development, the depth limits for extensions of more than one storey can apply to the whole extension, so we confirm which route applies before drawings are finalised.

Nearby

Close to Streatham? We work across the area, including:

Other extensions in Streatham

All two-storey extension services in Streatham · Part single, part two-storey extensions across Greater London

The quickest next step is a visit. We'll look at your house in Streatham and give you an honest view of the options.