Move
Total: £67,275
- SDLT (HMRC)
- £38,250
- Estate-agent fee
- £8,850
- Survey
- £1,500
- Legal (sale + purchase)
- £2,500
- Removals
- £2,000
- Chain contingency (1.5%)
- £14,175
Stamp duty vs extension costs in Southwark — 2026 guide
For homeowners in Southwark (London Borough of Southwark). Updated 2026-06-11.
Inner south London. Highly heterogeneous: Georgian terraces in Camberwell Grove; Victorian terraces in East Dulwich (SE22), Peckham (SE15), Nunhead and Camberwell; planned Victorian suburb in Dulwich Village; substantial postwar council estates and recent regeneration around Bermondsey and Elephant & Castle. Side returns extremely common across the eastern wards.
The borough covers the SE1, SE5, SE15, SE16, SE17, SE21, SE22, SE24, SE26 postcode districts. Terraced homes here trade around £875,000 against the borough-wide £590,000 average.
In short
In Southwark, the average home is valued at £590,000. Moving up by 60% to a £945,000 property triggers approximately £38,250 in Stamp Duty Land Tax (SDLT). By contrast, a 12 m² high-spec side return extension here costs around £82,524 all-in. The average home here is around £590,000 (ONS, 2026).
Your numbers
Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.
Your result
Moving is £15,249 cheaper than extending
Extend
Side return extension — high spec
Total: £82,524
- Build cost (12 m² × £4,600/m²)
- £55,200
- Professional fees (15%)
- £8,280
- Subtotal
- £63,480
- VAT (20%)
- £12,696
- Contingency (10%)
- £6,348
An extension of this type and size could add roughly £76,700 (≈13%) to your home's value — Nationwide Building Society, October 2025.
Your tipping line
Where moving starts costing more than the extension you selected. The chart follows your inputs above.
Up to about £1,080,000 of target price, moving is the cheaper route in Southwark; beyond that line, extending wins.
Extending in Southwark: what's different here
Local planning picture
- Conservation areas
- 48
- Householder decisions within 8 weeks
- 78%
- Build-cost tier
- inner London
- Typical housing stock
- Victorian and Edwardian terraces
Decision speed: MHCLG householder statistics, year ending September 2025, excluding agreed extensions of time.
Worth knowing in Southwark
- The average home here is around £590,000 (ONS, 2026).
- Extension types suited to Victorian and Edwardian terraces: Side return extension, Rear extension (single storey), Wrap-around extension, Kitchen extension, Loft conversion (dormer), Loft conversion (mansard).
How the £38,250 stamp duty stacks up
HMRC bands applied to a £945,000 purchase — the default Southwark trade-up.
| Price band | Rate | SDLT due |
|---|---|---|
| £0 – £125,000 | 0% | £0 |
| £125,000 – £250,000 | 2% | £2,500 |
| £250,000 – £925,000 | 5% | £33,750 |
| £925,000 – £1,500,000 | 10% | £2,000 |
What each suitable type costs vs the £67,275 move
High specification at typical size, inner London rates, all-in.
| Extension type | All-in cost | vs moving |
|---|---|---|
| Side return extension (12 m²) | £82,524 | £15,249 more than moving |
| Rear extension (single storey) (22 m²) | £124,982 | £57,707 more than moving |
| Wrap-around extension (25 m²) | £108,388 | £41,113 more than moving |
| Kitchen extension (22 m²) | £124,982 | £57,707 more than moving |
| Loft conversion (dormer) (18 m²) | £47,093 | saves £20,182 vs moving |
| Loft conversion (mansard) (30 m²) | £103,155 | £35,880 more than moving |
Why this comparison matters
"Homeowners that add a loft conversion or extension, incorporating a large double bedroom and bathroom, can add as much as 24% to the value of a three-bedroom, one-bathroom house."
Frequently asked questions
- Is it cheaper to extend or move in Southwark?
- At Southwark's average £590,000 home moving up to £945,000, the move costs about £67,275 — including £38,250 of HMRC Stamp Duty. A 12 m² high-spec side return extension runs roughly £82,524 at inner London rates. Moving is cheaper here by about £15,249. Your real figure depends on extension size, specification and planning constraints.
- Do I need planning permission for an extension in Southwark?
- Many single-storey rear extensions fall under Permitted Development — no planning permission needed. Southwark operates Article 4 directions in named conservation areas — notably the Dulwich Village and East Dulwich Grove conservation areas (high-restriction), Camberwell Grove, Peckham Rye, and Bermondsey Spa. A borough-wide HMO Article 4 also applies. Southwark has 48 conservation areas, including Dulwich Village, East Dulwich Grove, Camberwell Grove, where PD rights are curtailed. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the London Borough of Southwark planning portal first. Open the London Borough of Southwark planning portal
- How long does a side return extension take in Southwark?
- Allow around 16 weeks on site for a typical side return extension in Southwark, after design, party wall agreements with neighbours and the council's determination period. A rear extension (single storey) runs nearer 16 weeks. End to end, plan 4–8 months from first call to completion — longer in conservation areas or where structural surveys are needed.
- How much value does an extension add in Southwark?
- On a £590,000 Southwark home, the uplift is roughly £76,700 to £141,600: Nationwide Building Society (October 2025) put an extra double bedroom at about 13% of value, and a full loft conversion plus extension at up to 24%. The realised return depends on your street's ceiling price, buyer demand in Southwark and the specification you choose.
- Can I live in my home during the extension build?
- Most Southwark families stay in their home during a single-storey rear or side return extension — the build is contained to the back, and your kitchen is typically rebuilt in 2–3 weeks of disruption. Loft conversions and full wraparounds are harder: expect 4–6 weeks where one floor is unusable. Plan for temporary kitchen arrangements and dust everywhere.
- At what price does moving stop making sense in Southwark?
- Starting from Southwark's average £590,000 home with a 12 m² high-spec side return extension (£82,524 all-in), the tipping line sits at roughly £1,080,000: buying above that price costs more in SDLT and moving fees than the extension itself. Below it, moving stays the cheaper route. The live chart on this page recalculates the line for your own inputs.
- How much stamp duty would I pay moving up in Southwark?
- On a typical Southwark trade-up from £590,000 to £945,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £38,250 — an effective rate of 4.05%. First-time buyers and additional-property buyers pay different rates. Use HMRC's official calculator at tax.service.gov.uk for your exact figure. HMRC Stamp Duty calculator
- How much does an extension cost in Southwark in 2026?
- Budget around £83,000 all-in for a high-spec 12 m² side return extension here — inner London build rates run near £4,600/m². For a 22 m² rear extension (single storey) expect roughly £125,000. Those totals already carry 15% professional fees, 20% VAT and a 10% contingency; access, specification and ground conditions move the final number.
- How long does planning permission take in Southwark?
- The statutory determination period for a householder application is 8 weeks. London Borough of Southwark decided 78% of householder applications within 8 weeks in the year to September 2025 (MHCLG figures, excluding agreed extensions of time). Across London, authorities grant roughly low-to-mid 80s per cent of applications. A householder application costs £548 from April 2026, and a Larger Home Extension prior approval £240.
Compare nearby London boroughs
Nearby by average property value — useful if you're weighing a move to an adjacent price tier. A comparable trade-up in Barnet would carry the same £38,250 of stamp duty.
Methodology and sources
Stamp Duty Land Tax is calculated from the HMRC bands in force for the 2025–26 tax year. Verify any figure against HMRC's official calculator before committing. Extension costs use inner London £/m² rates by extension type — industry-estimate midpoints, presented as approximations.
- MHCLG planning statistics (PS2 dashboard) — householder decision speed, year ending September 2025.
- London 2026 £/m² grid by extension type and tier — Build Team benchmark compiled from BCIS/RICS, FMB and published architect guides (refreshed quarterly).
- Conservation-area counts and Article 4 status — individual London borough councils, verified 2026.
- HMRC SDLT calculator — tax.service.gov.uk/calculate-stamp-duty-land-tax
- GOV.UK Stamp Duty Land Tax guidance — gov.uk/stamp-duty-land-tax
- Nationwide House Price Index (October 2025 release) — value-add commentary attributed to Andrew Harvey, Senior Economist.
- HM Land Registry / ONS UK House Price Index — borough average property values (March 2026 release).