Should I Extend My London Home or Move? The Honest Comparison

The question of whether to extend an existing London home or sell and buy a larger one is one of the most financially significant decisions homeowners face. The answer depends on a combination of financial, practical, and personal factors — and a clear-headed comparison of the real costs on both sides is the starting point.

The cost of moving in London is typically underestimated. Stamp Duty Land Tax on a larger London property can be substantial — on a property at seven hundred and fifty thousand pounds, SDLT is currently twenty-five thousand pounds. At one million pounds it rises to forty-three thousand seven hundred and fifty pounds, and beyond this threshold the five and ten percent bands apply. Estate agent fees on the sale of your current property at one to one and a half percent of value, legal fees on both sale and purchase, survey costs, removal costs, and the time and disruption cost of the move together commonly total fifty to one hundred thousand pounds before any price premium for the larger property.

The cost of extending is typically more predictable and, critically, does not attract Stamp Duty. The value added to the property by a well-designed extension is typically higher than the cost — a rear extension costing sixty to eighty thousand pounds in a desirable London location commonly adds one hundred to one hundred and thirty thousand pounds to the market value, representing a meaningful return on investment.

However, extending is not always the better choice. If the existing property has fundamental limitations that an extension cannot address — wrong number of bedrooms, wrong school catchment area, location constraints, or a plot where extension is not feasible due to planning or physical constraints — then moving may be the only practical option regardless of financial comparisons.

The disruption comparison also matters. A full rear extension in a London house typically means six to ten months of construction on your doorstep, with disruption at the rear and often for the rear rooms of the house during the most active phases. Moving involves a period of transition but then a clean break. For families with young children, the disruption calculus may favour moving.

Financially, the break-even analysis depends on the specific numbers for each homeowner. If moving up to a larger property requires buying at seven hundred and fifty thousand pounds more than the sale price (for a similar quality and location), the total transaction cost of moving may be seventy-five to one hundred thousand pounds or more — comparable to the cost of a significant extension, with no SDLT and with value added rather than spent on transaction costs.

The sweet spot for extending is typically: you love the location and want to stay, the property has feasible extension potential (space, planning prospects), the extension would address your space needs, and the transaction cost of moving would be comparable or higher than the extension cost.

RCB can advise on extension feasibility and likely value-add for your specific London property as part of our free pre-consultation service. +44 7359 872594 | connect@rcbGroup.co.uk | www.rcbGroup.co.uk