New Build vs Extension: Which Adds More Value to Your Home in London?
Updated: Oct 16
One of the most important decisions facing London homeowners with a large garden or aging property is whether to extend the existing house or demolish and build a new one. Both options can add significant value — but they work very differently in terms of cost, timeline, VAT treatment and the scale of return they generate. LCCL Construction delivers both house extensions and new build construction across London, Hertfordshire and Bedfordshire and can advise on the right approach for your specific situation.
Which Adds More Value New Build vs Extension — a New Build or an Extension?
New Build vs Extension In absolute terms a new build typically adds more total value than an extension — because it creates an entirely new property rather than adding to an existing one. A new build on a garden plot in North London can create a property worth £600,000 to £1,200,000 from a plot that may have cost £200,000 to £400,000 — a value creation of £400,000 to £800,000. However a house extension generating a return of 150 to 250 per cent on a £70,000 investment is also outstanding. The right comparison depends on your specific situation.
Return on Investment: New Build vs Extension
House extension ROI: A wraparound extension costing £80,000 typically adds £120,000 to £180,000 in value — a return of 150 to 225 per cent. See our full guide on how much value an extension adds. New build ROI: A new build house costing £320,000 to construct on a plot costing £250,000 creates a property worth £700,000 to £900,000 in many London and Hertfordshire locations — a return of 30 to 70 per cent on total investment including land. The percentage return is lower than an extension but the absolute value created is far greater. See our guide on new build house costs.
The VAT Advantage of New Builds
New build residential construction is zero-rated for VAT. Extensions are subject to 20 per cent VAT. On a £400,000 new build construction project this saves £80,000 compared with an equivalent renovation or extension. This significantly improves the economics of new build over large-scale extension or renovation projects and is one reason why replacement dwelling projects have become increasingly popular across London and Hertfordshire.
When a New Build Adds More Value Than an Extension
A new build is likely the better value option when: the existing property is in poor structural condition requiring significant renovation costs, the plot is large enough to accommodate a substantially larger replacement dwelling, the VAT saving on a large construction budget is financially significant, or you are building on a garden plot or infill site where no existing property currently stands. See our full comparison guide at new build vs extension.
When an Extension Adds More Value Than a New Build
An extension is likely the better option when: the existing property has strong period character that is worth preserving, the budget is £40,000 to £200,000 rather than £300,000+, you want to stay in your home during works, the timeline needs to be under 12 months, or permitted development means you can build without planning permission. For most London homeowners a well-designed extension is the highest-return investment available on their existing property.
Frequently Asked Questions
Does a new build or extension add more value per pound spent?
An extension typically generates a higher percentage return — 150 to 250 per cent — than a new build in percentage terms. A new build generates a larger absolute value uplift but requires significantly more capital.
Is VAT charged on both new builds and extensions?
Extensions are subject to 20 per cent VAT. New build residential construction is zero-rated — no VAT charged. This is a major financial advantage for new builds at scale.
To discuss whether a new build or extension is right for your property call LCCL Construction on 020 8037 7332 or get an instant quote online.
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