How Much Does a Double-Storey Extension Cost?
£40,000 – £110,000
depending on size
A double-storey extension costs between £40,000 and £110,000, making it one of the most significant home improvement projects a homeowner can undertake. Doubling the storey height roughly adds 50-70% to the cost of a single-storey extension, but delivers twice the floor area. Planning permission is typically required for double-storey extensions.
Average cost
£40,000 – £110,000
depending on size
Prices vary by region, property type and tradesperson. Always get at least two quotes.
What affects the price?
Footprint and floor area - a 4x4m double-storey extension adds 32m2 of new space; larger footprints cost proportionately more
Specification - standard brick finish and basic internal spec vs stone cladding, high-spec glazing, and premium finishes
Planning permission - double-storey extensions almost always need planning permission, adding £2,000-£4,000 in architect and application fees
Structural complexity - two floors require more substantial foundations and structural steelwork than a single-storey equivalent
Labour vs materials
Labour accounts for 40-50% of the total build cost. A double-storey extension typically takes 16-24 weeks from groundworks to practical completion.
Questions to ask your tradesperson
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