Moving House vs Extending in London (2025): The Real Cost Comparison

The decision between moving to a bigger house and extending your current one is fundamentally a financial calculation — but it also involves lifestyle factors, certainty of outcome, and construction risk. Here's how to compare them honestly.

The True Cost of Moving

Moving to a larger London property involves more costs than most people account for:

Stamp Duty Land Tax (SDLT): On a £700,000 purchase, SDLT is approximately £22,500 (at 2025 rates for a primary residence). On a £900,000 purchase, approximately £33,750.

Estate agent fees (selling): 1–2% of the sale price. On a £600,000 sale: £6,000–£12,000.

Conveyancing costs: £1,500–£4,000 for both sale and purchase combined.

Mortgage arrangement fees: £1,000–£2,000 for a new product.

Removals: £1,000–£3,000 for a family-sized move within London.

Immediate decoration/renovation costs in the new property: Almost always required — flooring, decoration, kitchen or bathroom updates.

Total typical moving cost (before renovation): £35,000–£55,000 on a £600k sale / £800k purchase. And you may still need to extend or refurbish the new property.

The Cost of Extending and Staying

A single-storey rear extension in London typically costs £45,000–£75,000 for a medium specification. A loft conversion £35,000–£65,000. For a combined rear extension plus loft conversion: £80,000–£135,000.

This creates meaningful new floor area — typically 15–25m² per project — in the home you already own, know, and live in.

The Financial Comparison

The extension creates value directly in your existing property. The "cost" of extending is the construction cost; the "cost" of moving includes SDLT, agents, legal fees, and the premium for buying a larger property vs. adding space to what you own.

For many London homeowners, the moving cost alone (£35,000–£55,000) would fund the design and structural works for a rear extension — leaving the full build cost to be addressed separately.

When Moving Makes More Sense

• You need more than one additional room and extension is not physically achievable
• The location is wrong — you want to move borough or street
• The property has structural or legal problems that make extension difficult
• You dislike the house itself and want something architecturally different
• Your mortgage position makes remortgaging and borrowing for renovation impractical

When Extending Makes More Sense

• You are happy with the location, the street, and the neighbours
• The property has genuine extension potential (adequate rear garden depth, permitted development rights available)
• The additional space you need is achievable through loft conversion, rear extension, or a combination
• You have or can access borrowing for the build cost
• Moving costs alone are significant enough to fund substantial renovation

RCB Design & Build

RCB Design & Build helps homeowners assess extension feasibility and estimate accurately — so the comparison between staying and moving can be made on real numbers, not guesswork.