Move
Total: £56,610
- SDLT (HMRC)
- £30,750
- Estate-agent fee
- £7,635
- Survey
- £1,500
- Legal (sale + purchase)
- £2,500
- Removals
- £2,000
- Chain contingency (1.5%)
- £12,225
Hounslow: is it cheaper to extend or move in 2026?
For homeowners in Hounslow (London Borough of Hounslow). Updated 2026-06-11.
West London. Substantial Victorian and Edwardian terrace stock in Chiswick (W4); planned Bedford Park suburb tightly restricted; 1930s and postwar housing in Hounslow, Isleworth, Heston and Cranford. Side returns common in Chiswick; rear and loft elsewhere.
The borough covers the TW3, TW4, TW5, TW7, TW8, TW9, TW13, TW14, W4 postcode districts. Terraced homes here trade around £615,000 against the borough-wide £509,000 average.
In short
In Hounslow, the average home is valued at £509,000. Moving up by 60% to a £815,000 property triggers approximately £30,750 in Stamp Duty Land Tax (SDLT). By contrast, a 22 m² high-spec rear extension (single storey) here costs around £108,537 all-in. The average home here is around £509,000 (ONS, 2026).
Your numbers
Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.
Your result
Moving is £51,927 cheaper than extending
Extend
Rear extension (single storey) — high spec
Total: £108,537
- Build cost (22 m² × £3,300/m²)
- £72,600
- Professional fees (15%)
- £10,890
- Subtotal
- £83,490
- VAT (20%)
- £16,698
- Contingency (10%)
- £8,349
An extension of this type and size could add roughly £66,170 (≈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 £1,319,000 of target price, moving is the cheaper route in Hounslow; beyond that line, extending wins.
Extending in Hounslow: what's different here
Local planning picture
- Conservation areas
- 28
- Householder decisions within 8 weeks
- 58%
- Build-cost tier
- outer London
- Typical housing stock
- 1930s semi-detached homes
Decision speed: MHCLG householder statistics, year ending September 2025, excluding agreed extensions of time.
Worth knowing in Hounslow
- The average home here is around £509,000 (ONS, 2026).
- Extension types suited to 1930s semi-detached homes: Rear extension (single storey), Rear extension (double storey), Two-storey side extension, Garage conversion, Loft conversion (hip-to-gable), Over-garage extension.
How the £30,750 stamp duty stacks up
HMRC bands applied to a £815,000 purchase — the default Hounslow trade-up.
| Price band | Rate | SDLT due |
|---|---|---|
| £0 – £125,000 | 0% | £0 |
| £125,000 – £250,000 | 2% | £2,500 |
| £250,000 – £925,000 | 5% | £28,250 |
What each suitable type costs vs the £56,610 move
High specification at typical size, outer London rates, all-in.
| Extension type | All-in cost | vs moving |
|---|---|---|
| Rear extension (single storey) (22 m²) | £108,537 | £51,927 more than moving |
| Rear extension (double storey) (45 m²) | £208,553 | £151,943 more than moving |
| Two-storey side extension (35 m²) | £167,440 | £110,830 more than moving |
| Garage conversion (18 m²) | £43,056 | saves £13,554 vs moving |
| Loft conversion (hip-to-gable) (25 m²) | £67,275 | £10,665 more than moving |
| Over-garage extension (18 m²) | £34,983 | saves £21,627 vs 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 Hounslow?
- At Hounslow's average £509,000 home moving up to £815,000, the move costs about £56,610 — including £30,750 of HMRC Stamp Duty. A 22 m² high-spec rear extension (single storey) runs roughly £108,537 at outer London rates. Moving is cheaper here by about £51,927. Your real figure depends on extension size, specification and planning constraints.
- How long does planning permission take in Hounslow?
- The statutory determination period for a householder application is 8 weeks. London Borough of Hounslow decided 58% of householder applications within 8 weeks in the year to September 2025 (MHCLG figures, excluding agreed extensions of time). About 71% of applications here were granted (MHCLG, Q3 2025). 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 Hounslow?
- Many single-storey rear extensions fall under Permitted Development — no planning permission needed. Hounslow has Article 4 directions covering conservation areas in Chiswick (including Bedford Park — shared with Ealing) and an HMO Article 4. The Bedford Park direction removes most external alteration PD rights and is one of the most restrictive in West London. Hounslow has 28 conservation areas, including Bedford Park, Chiswick Mall, Strand-on-the-Green, where PD rights are curtailed. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the London Borough of Hounslow planning portal first. Open the London Borough of Hounslow planning portal
- How long does a rear extension (single storey) take in Hounslow?
- Allow around 16 weeks on site for a typical rear extension (single storey) in Hounslow, after design, party wall agreements with neighbours and the council's determination period. A rear extension (double storey) runs nearer 20 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 Hounslow 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 Hounslow average of £509,000, that's roughly £66,200 to £122,200 of capital uplift. Final return depends on the local market, the type of buyer in Hounslow, and your extension's specification.
- Can I live in my home during the extension build?
- Most Hounslow families stay in their home during a rear extension or garage conversion — works are contained to one side of the house. Two-storey side extensions and hip-to-gable lofts are noisier: expect 4–6 weeks where one floor or the driveway side is out of action. Plan temporary kitchen arrangements and dust control for the noisy weeks.
- At what price does moving stop making sense in Hounslow?
- Starting from Hounslow's average £509,000 home with a 22 m² high-spec rear extension (single storey) (£108,537 all-in), the tipping line sits at roughly £1,319,000: 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 Hounslow?
- On a typical Hounslow trade-up from £509,000 to £815,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £30,750 — an effective rate of 3.77%. 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 Hounslow in 2026?
- A 22 m² rear extension (single storey) in Hounslow runs about £109,000 all-in at high specification, on outer London build rates of around £3,300/m². A 45 m² rear extension (double storey) comes to roughly £209,000. All-in figures include 15% professional fees, 20% VAT and a 10% contingency — final cost depends on access, specification and ground conditions.
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 Bromley would carry about £31,500 of stamp duty — £750 more than in Hounslow.
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 outer London £/m² rates by extension type — industry-estimate midpoints, presented as approximations.
- 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
- 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.