Extend and Improve vs. Move House: How London Homeowners Should Decide

Your family has grown, your home feels too small, and you are facing a question that thousands of London homeowners ask every year: is it better to extend and improve what you have, or sell up and buy somewhere bigger?

The answer is rarely straightforward. It depends on your current property, your target, the market, your finances, and your timeline. But there is a structured way to think through the decision, and for many London homeowners the conclusion is that extending and improving is the far better financial choice.

The first step is to calculate the real cost of moving, not just the sale price and purchase price difference.

Stamp Duty Land Tax (SDLT)

Stamp Duty is often the single largest cost of moving, particularly at London prices. SDLT applies to the purchase price of the new property. Main residence rates (2025 onwards, after the temporary reduction reverted):

• Up to £125,000: 0%
• £125,001 to £250,000: 2%
• £250,001 to £925,000: 5%
• £925,001 to £1.5m: 10%
• Above £1.5m: 12%

For a typical London move — say, buying a family home at £700,000 — the SDLT is approximately £22,500. At £850,000, it is £32,500. This money is gone immediately and generates no return.

First-time buyers benefit from relief up to £425,000 (0% on the first £425,000, 5% on the next £200,000 up to £625,000). But by definition, if you are already a homeowner considering moving up, FTB relief does not apply.

Additional homes surcharge: If you are in a position of owning two properties simultaneously (before completing the sale of your existing home), the SDLT surcharge of 3% on the full purchase price applies. For a £700,000 property this adds £21,000. Even if you reclaim this surcharge after selling your main home within three years, the cashflow impact is significant.

Estate agent fees

Typically 1–3% of the sale price. On a £600,000 London house, this is £6,000 – £18,000. Most London agents charge 1.0–1.5% plus VAT.

Legal fees

Conveyancing for both sale and purchase: typically £2,500 – £5,000 total in London.

Mortgage arrangement fees, broker fees, and survey costs

Mortgage arrangement fees: £0 – £2,000 depending on the product. Survey on the new property: £600 – £2,000 depending on the type (HomeBuyer Report or full structural survey). Broker fees: £0 – £1,000.

Removal costs

A standard residential move within London: £1,000 – £4,000 for a removal company depending on volume and distance.

Renovation and decoration at the new property

Very few people buy a property and are completely satisfied with it. Budget realistically for any work you will want to do — new kitchen, redecorated throughout, new bathrooms, carpets. Even for a property in good overall condition, £15,000 – £40,000 for modernisation is common.

Total transaction costs

Putting it together for a typical London move from a £600,000 property to a £750,000 property:

• Estate agent fees on sale (1.25%): £7,500
• Conveyancing (both sides): £4,000
• SDLT: £27,500
• Survey and mortgage fees: £2,000
• Removal: £2,500
• Renovation at new property: £20,000

Total: approximately £63,500 — before any renovation work at the new house, just the pure transaction friction.

This is the amount you are spending to change address. It is not adding any space, improving any room, or building any value. It is pure friction.

In London, £60,000 – £70,000 can buy you:

• A well-specified single-storey rear extension of 15–20m2, with bifold doors, underfloor heating, and a new open-plan kitchen
• A loft conversion with a bedroom and en-suite bathroom
• A full refurbishment of a 3-bedroom house including new kitchen, new bathrooms, new flooring, plastering, and redecorating throughout

The extension or refurbishment keeps you in a property you know, in a street you have chosen, in a school catchment you value — and it creates space that is valued by the market when you do eventually sell.

Extending and improving is generally the better choice when:

You love where you live: Location is the one thing you genuinely cannot change. If you like your street, your neighbours, the local schools, the walk to the tube, the park — that is worth a great deal. Extending keeps you there.

The gap between what you have and what you need can be bridged by building: If you need one or two more rooms and your planning situation allows it, building is typically cheaper than buying.

The market is hot and moving up the property ladder is expensive: In rising markets, the properties you want to buy go up in price as fast as yours. The transaction costs grow proportionately.

Your current property has untapped potential: Many London homes can be significantly improved — rear extensions, loft conversions, side returns, basement conversions. If your property has these options and you haven't used them, you are sitting on unrealised value.

You want certainty: Selling is uncertain. Chains break. Buyers pull out. Deals fall through. An extension project is within your control — it will complete if you appoint the right people.

Moving is the better choice when:

The extension cannot solve the problem: If you need a much larger garden, a different location, a completely different type of property — these things cannot be built. Moving is the only answer.

Planning constraints make meaningful extension impossible: Some London properties, particularly in dense conservation areas, on small plots, or with restrictions on what can be built, cannot accommodate the extension you need.

The property has fundamental issues: If there are severe structural problems, ongoing flood risk, or major building defects that exceed the investment justified by the location, moving may be better than investing further in a problematic property.

You are ready to move regardless: Sometimes the decision is lifestyle, not finance. A life change — new job, new relationship, children leaving home — may mean moving makes sense on its own terms. The financial analysis is a factor, not the only one.

A well-executed extension or loft conversion almost always adds value in London. The key factors:

Location premium is retained: The extension adds space at the same location premium as your existing property. If you are in a desirable street, adding 20m2 of excellent quality kitchen-living space adds value at the same premium per square metre that the market already assigns to your address.

Quality matters: A cheap or poorly executed extension can add little or even detract from value. A high-quality, well-designed extension with proper planning consent and Building Regulations sign-off adds proportionate value.

There is a ceiling: Adding the 6th bathroom to a 3-bedroom house will not add value proportionately. Improvements should match the property type and local market expectations.

Research comparable values: Look at recent sold prices of similar sized properties on your street and nearby streets. If extending from 3 bedrooms to 4 increases your house value from £650,000 to £750,000+, and the extension costs £60,000–£70,000, the ROI is compelling.

1. Calculate the total cost of moving (including SDLT, fees, and renovation at the new property) to what you actually want
2. Get indicative extension costs from a reputable contractor for what you would need to build
3. Estimate the value added by the extension based on comparable sales in your area
4. Compare: If cost of move > cost of building + renovation AND the extended property gives you what you need, extend
5. Add the qualitative factors: Location, school catchment, certainty of outcome, disruption tolerance, long-term plans

For most London homeowners in established areas who need one or two more rooms, extending is the better financial decision by a clear margin. The stamp duty alone on a typical London upgrade purchase often exceeds the cost of a meaningful extension.

We work with London homeowners in exactly this position — helping them understand what their current property can become, what it would cost to build, and how to approach the project with confidence. We provide pre-construction budgets and scope reviews so you can make the decision with real numbers rather than guesswork.

If you are weighing up whether to extend or move, contact us for an initial conversation. We are happy to discuss your options without obligation.