House Extension Cost in Sevenoaks — 2026 Prices
A typical house extension in Sevenoaks runs £42,000–£120,000 all-in based on quotes we've written over the past two years across the TN13, TN14, TN15 postcodes. The mid-range — roughly £48,300–£102,000 — is where most Sevenoaks projects land once spec, finish level and structural complexity settle.
What drives house extension cost in Sevenoaks
Sevenoaks's typical housing stock — Edwardian villas, inter-war detacheds, Riverhead & Seal stock — has a big effect on cost. Conservation overlays around Knole Park (National Trust) can push joinery and roofing spec up by 10–15% because of matching tile, lime mortar or sash detailing.
- • Structural complexity (RSJs, foundations, knock-throughs)
- • Conservation / Article 4 detailing on listed or near-listed stock
- • Spec of kitchen, bathroom, joinery and flooring
- • Access — terrace, narrow lane, off-street parking
- • Whether you stay on site or move out
Itemised cost breakdown
Every Sevenoaks house extension quote we send breaks down into these lines so you can compare like-for-like with other builders.
- • Site set-up, scaffold, skip, welfare — £1,680–£6,000
- • Structural & foundations — £7,560–£26,400
- • Shell, roofing, glazing — £9,240–£31,200
- • M&E (plumbing, electrics, heating) — £5,040–£18,000
- • Joinery, kitchen / bathroom, finishes — £11,760–£38,400
- • Contingency (10%) — held back, not spent unless needed
Our Biddenden yard is 24 miles (~45-minute drive) from Sevenoaks, so we don't carry distance loadings into Sevenoaks quotes the way a London or coast-based contractor would. That alone is usually 8–12% off the headline number.
Below is the cost breakdown we use in every written Sevenoaks quote — labour, materials, structural, finishes and a contingency line. No "from £X" headline pricing.
Sevenoaks cost FAQs
Is Sevenoaks more expensive than other parts of Kent for a house extension?
Marginally — Sevenoaks's TN13, TN14, TN15 postcode runs about 3–6% above the Kent average, mostly because of conservation detail and parking constraints near Knole Park (National Trust). The biggest cost variance is still spec, not postcode.
Will you provide a fixed-price quote or estimate?
Fixed-price written quote — itemised across the lines above, with a 10% contingency you only pay if it's actually used. We've worked on High Street and surrounding Sevenoaks streets so we price from real local knowledge, not desktop assumptions.
What's the deposit and payment schedule?
10% on contract signing, then stage payments tied to milestones (slab down, weathertight, first fix, second fix, completion). Final 5% retained for 4 weeks post-handover.
Do you include VAT in quotes?
Yes — every Sevenoaks quote is VAT-inclusive. We're VAT-registered. Some listed-building work in Sevenoaks qualifies for reduced-rate VAT; we'll flag this if applicable.
Get a real house extension price for your Sevenoaks property
Free site visit, written itemised quote within 5 working days. No "from" pricing — actual numbers for your address.
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In short
Most house extension projects in Sevenoaks land between £48,300–£102,000 all-in. The fastest way to get a real number for your TN13, TN14, TN15 address is a 30-minute site visit followed by an itemised written quote.