Move
Total: £52,525
- SDLT (HMRC)
- £28,000
- Estate-agent fee
- £7,125
- Survey
- £1,500
- Legal (sale + purchase)
- £2,500
- Removals
- £2,000
- Chain contingency (1.5%)
- £11,400
Stamp duty vs extension costs in Lewisham — 2026 guide
For homeowners in Lewisham (London Borough of Lewisham). Updated 2026-06-11.
Inner south-east London. Substantial Victorian and Edwardian terrace stock — Brockley, Telegraph Hill, Forest Hill, Hither Green, Sydenham. Side returns common across the borough.
The borough covers the BR1, SE3, SE4, SE6, SE8, SE10, SE12, SE13, SE14, SE23, SE26 postcode districts. Terraced homes here trade around £590,000 against the borough-wide £475,000 average.
In short
In Lewisham, the average home is valued at £475,000. Moving up by 60% to a £760,000 property triggers approximately £28,000 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 £475,000 (ONS, 2026).
Your numbers
Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.
Your result
Moving is £29,999 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 £61,750 (≈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 £1,095,000 of target price, moving is the cheaper route in Lewisham; beyond that line, extending wins.
Extending in Lewisham: what's different here
Local planning picture
- Conservation areas
- 26
- Householder decisions within 8 weeks
- 71%
- 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 Lewisham
- The average home here is around £475,000 (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 £28,000 stamp duty stacks up
HMRC bands applied to a £760,000 purchase — the default Lewisham trade-up.
| Price band | Rate | SDLT due |
|---|---|---|
| £0 – £125,000 | 0% | £0 |
| £125,000 – £250,000 | 2% | £2,500 |
| £250,000 – £925,000 | 5% | £25,500 |
What each suitable type costs vs the £52,525 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 | £29,999 more than moving |
| Rear extension (single storey) (22 m²) | £124,982 | £72,457 more than moving |
| Wrap-around extension (25 m²) | £108,388 | £55,863 more than moving |
| Kitchen extension (22 m²) | £124,982 | £72,457 more than moving |
| Loft conversion (dormer) (18 m²) | £47,093 | saves £5,432 vs moving |
| Loft conversion (mansard) (30 m²) | £103,155 | £50,630 more than moving |
Why this comparison matters
"Authorities granted 90% of these applications and decided 93% within eight weeks or the agreed time."
Frequently asked questions
- Is it cheaper to extend or move in Lewisham?
- At Lewisham's average £475,000 home moving up to £760,000, the move costs about £52,525 — including £28,000 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 £29,999. Your real figure depends on extension size, specification and planning constraints.
- How much stamp duty would I pay moving up in Lewisham?
- On a typical Lewisham trade-up from £475,000 to £760,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £28,000 — an effective rate of 3.68%. 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
- What does a typical extension cost in Lewisham in 2026?
- A 12 m² side return extension in Lewisham runs about £83,000 all-in at high specification, on inner London build rates of around £4,600/m². A 22 m² rear extension (single storey) comes to roughly £125,000. All-in figures include 15% professional fees, 20% VAT and a 10% contingency — final cost depends on access, specification and ground conditions.
- How long does planning permission take in Lewisham?
- The statutory determination period for a householder application is 8 weeks. London Borough of Lewisham decided 71% 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.
- Do I need planning permission for an extension in Lewisham?
- Many single-storey rear extensions fall under Permitted Development — no planning permission needed. Lewisham operates Article 4 directions in named conservation areas (Blackheath, Brockley, Telegraph Hill, Forest Hill among others) and a borough-wide HMO Article 4. Lewisham has 26 conservation areas, including Blackheath (Lewisham portion), Brockley, Telegraph Hill, where PD rights are curtailed. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the London Borough of Lewisham planning portal first. Open the London Borough of Lewisham planning portal
- How long does a side return extension take in Lewisham?
- Allow around 16 weeks on site for a typical side return extension in Lewisham, 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.
- Will an extension add value to my Lewisham home?
- Nationwide Building Society (October 2025) found that adding a double bedroom can lift a home's value by about 13%, and a full loft conversion plus extension by up to 24%. On a Lewisham average of £475,000, that's roughly £61,800 to £114,000 of capital uplift. Final return depends on the local market, the type of buyer in Lewisham, and your extension's specification.
- Can I live in my home during the extension build?
- Most Lewisham 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 Lewisham?
- Starting from Lewisham's average £475,000 home with a 12 m² high-spec side return extension (£82,524 all-in), the tipping line sits at roughly £1,095,000: 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.
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 Greenwich would carry about £27,500 of stamp duty — £500 less than in Lewisham.
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.
- 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).
- 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