Moving to a bigger house costs money that adds no space: stamp duty, estate agent fees, legal fees, surveys and removals. On a typical south-west London home these can reach tens of thousands of pounds before you pay the higher price of the bigger house. Extending keeps that money in your home. At Prohaus, a straightforward rear or side extension starts from £60,000 plus VAT and a loft conversion from £50,000 plus VAT. Extending usually wins if you like your area, your plot can take more space and the planning position is workable. Moving wins if you need far more space than the house can give, or a different location.
Key takeaways
- Stamp duty alone on a £1.2 million purchase is £63,750 at standard rates for a main home.
- Moving costs are “dead money”: none of it adds a square metre.
- Extension and loft costs add space and usually add value, though not always pound for pound.
- The house, the plot and the planning position decide whether extending is realistic.
- Disruption is real in both cases: months of building work, or months of selling, buying and chain risk.
01What does moving really cost?
These are the costs of moving that do not buy you any extra space.
| Cost | Typical basis |
|---|---|
| Stamp duty land tax (SDLT) | Charged in bands on the purchase price (see below) |
| Estate agent fee on your sale | Usually a percentage of the sale price, plus VAT |
| Conveyancing on sale and purchase | Solicitor fees plus searches and disbursements |
| Survey on the new home | Depends on survey level and property value |
| Mortgage arrangement and valuation fees | Depends on lender |
| Removals and storage | Depends on volume and distance |
| Work on the new house | New houses rarely suit you perfectly on day one |
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Stamp duty: the largest single cost
Standard SDLT rates for a main home (not a first-time buyer) are:
| Portion of the price | Rate |
|---|---|
| Up to £125,000 | 0% |
| £125,001 to £250,000 | 2% |
| £250,001 to £925,000 | 5% |
| £925,001 to £1.5 million | 10% |
| Above £1.5 million | 12% |
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Worked examples:
| Purchase price | SDLT at standard rates |
|---|---|
| £900,000 | £35,000 |
| £1,200,000 | £63,750 |
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Rates can change, so check the GOV.UK calculator for your purchase.
02What does extending cost?
| Project | Prohaus guide price (plus VAT) | Typical space added |
|---|---|---|
| Single-storey rear or side extension | From £60,000 | Larger kitchen, dining and family room |
| Loft conversion | From £50,000 | Bedroom with en-suite |
| Larger renovation or conversion | From £100,000 | Reconfigured house, often with extension |
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Add professional fees, approvals and VAT. Our house extension cost guide and loft conversion types and costs guide explain every cost driver.
03Example: a family needing one more bedroom and a bigger kitchen
A family in a £900,000 Victorian terrace in Putney wants a fourth bedroom and an open-plan kitchen.
Option A: move to a £1.2 million house nearby. SDLT on the purchase alone is £63,750, before agent fees on the sale, legal fees, survey and removals. They also need to borrow or find the £300,000 price difference.
Option B: extend. A side return or rear extension for the kitchen and a rear dormer loft conversion for the bedroom. The build cost is higher than a single project, but none of it goes on tax or fees, and the family keeps their street, school and neighbours.
The numbers depend on the house and the specification, which is why an itemised quote after a site visit matters.
04When does extending make more sense?
- You like your area, schools and commute.
- Your house has room to grow: a usable loft, a side return, or a garden that can take a rear extension.
- The planning position is workable. Read our planning permission guide.
- The finished house will not be far more valuable than others on the street (the “ceiling price”).
- You can live with building work, or arrange to move out for the noisiest stage.
05When does moving make more sense?
- You need much more space than the plot or planning rules allow.
- You want a different area or a garden the current house cannot offer.
- Conservation or listed status makes the changes you want unlikely. See our conservation area guide.
- The cost of extending would push the house well above local values.
06The questions to answer before you decide
- How much space do you need, and where: kitchen, bedrooms, office?
- Can the loft, side return, rear or garden provide it?
- What would the planning route be?
- What would the extension cost, from a real quote?
- What would moving cost, from real agent, legal and SDLT figures?
- What would each option leave your house worth, from a local agent?
- How would each option affect daily life for the next year?
07Frequently asked questions
Is it cheaper to extend or move in London?
For many families who like their area, extending is cheaper because no money goes on stamp duty and fees. Moving can be better value if you need much more space than your house can offer.
Does an extension add value?
An extension that adds well-designed living space or a bedroom generally adds value, but not always as much as it costs. A local estate agent can tell you the likely ceiling price for your street.
Is a loft conversion cheaper than moving?
Often. A Prohaus loft conversion starts from £50,000 plus VAT, which can be less than the stamp duty on a larger home.
Can I live at home while extending?
Usually, with planning. See our guide to living at home during building work.
What about a garden office instead of moving?
If the main need is a place to work, a garden office can be the simplest answer.
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Services and areas mentioned in this guide:
About Prohaus
Prohaus Ltd is a building company based in Kingston upon Thames, registered in 2015 and built on more than 20 years of residential building experience. We carry out extensions, loft conversions, renovations, new builds, kitchens and bathrooms, glazing, bespoke joinery and garden offices across Kingston, Surbiton, Richmond, Barnes, Putney, Fulham, Chelsea, Clapham and Wimbledon. Every project runs under a written contract with a 1-year guarantee.
Talk to us before you list your house
Send us your address and what you need from your home. We will look at the extension and loft options at a site visit and give you an itemised quotation to compare against the cost of moving.
