--- title: "Single vs Double-Storey Extensions: How to Choose | J&Co" description: "Single-storey vs double-storey extension comparison — cost per m², value uplift, planning and disruption. Honest 2026 guidance from a Hertfordshire builder." lang: en-GB json-ld: | [ { "@context": "https://schema.org", "@type": "Article", "headline": "Single vs Double-Storey Extensions: How to Choose", "description": "Single-storey vs double-storey extension comparison — cost per m², value uplift, planning and disruption. Honest 2026 guidance from a Hertfordshire builder.", "mainEntityOfPage": "https://jandco-contractorsltd.co.uk/guides/single-vs-double-storey-extensions/", "datePublished": "2026-05-07", "dateModified": "2026-05-07", "author": { "@type": "Person", "name": "Jamie Pocock", "jobTitle": "Owner & Lead Contractor", "worksFor": { "@id": "https://jandco-contractorsltd.co.uk/#business" } }, "publisher": { "@type": "Organization", "name": "J&Co Contractors", "url": "https://jandco-contractorsltd.co.uk" }, "image": [ "https://jandco-contractorsltd.co.uk/assets/upload-009-DFap0EVo.jpeg" ] }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "Is double-storey always better value than single-storey?", "acceptedAnswer": { "@type": "Answer", "text": "Per m², yes — the cost-per-m² is consistently lower because foundations and roof spread across more area. In absolute pounds spent it's higher. The right choice depends on whether you need an extra bedroom and whether the budget supports it." } }, { "@type": "Question", "name": "Will double-storey planning be harder to get?", "acceptedAnswer": { "@type": "Answer", "text": "Usually yes — double-storey extensions have stricter PD limits and more often need full planning permission. Approval rates are still high in Hertfordshire and Essex if the design is sympathetic to the existing house and respects neighbour amenity. Architect-led design helps." } }, { "@type": "Question", "name": "Can I extend single-storey now and add a second floor later?", "acceptedAnswer": { "@type": "Answer", "text": "Possible but expensive — the original foundations have to be designed for future double-storey loading from day one (otherwise they need underpinning later). Cheaper to commit to double-storey upfront if you know you want it. Otherwise, plan single-storey for what it is." } }, { "@type": "Question", "name": "How much disruption does each cause?", "acceptedAnswer": { "@type": "Answer", "text": "Single-storey: moderate — kitchen out for 4–6 weeks, scaffold, dust, daily site activity. Double-storey: significant — full scaffold for longer, opening of first-floor wall, internal layout disruption. Many double-storey clients move out for final 4–6 weeks." } }, { "@type": "Question", "name": "Do I need separate quotes for each option?", "acceptedAnswer": { "@type": "Answer", "text": "Yes — quotes are scope-specific. We're happy to quote both single and double-storey on the same site so you can compare directly. The £/m² advantage of double-storey usually shows up clearly when seen side by side." } }, { "@type": "Question", "name": "What's most popular in Hertfordshire and Essex?", "acceptedAnswer": { "@type": "Answer", "text": "Roughly 65% of our extension projects are single-storey rear (kitchen-diner schemes), 25% double-storey, 10% side return or wrap-around. The trend over the last 3 years has been more double-storey as families weigh up moving costs against extending in place." } } ] }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://jandco-contractorsltd.co.uk/" }, { "@type": "ListItem", "position": 2, "name": "Building & Construction", "item": "https://jandco-contractorsltd.co.uk/building-construction/" }, { "@type": "ListItem", "position": 3, "name": "Extensions", "item": "https://jandco-contractorsltd.co.uk/building-extensions/" }, { "@type": "ListItem", "position": 4, "name": "Single vs Double-Storey Extensions: How to Choose", "item": "https://jandco-contractorsltd.co.uk/guides/single-vs-double-storey-extensions/" } ] } ] --- We use essential cookies to run this site, and optional cookies only with your consent. [Cookie policy](/cookie-policy/) AcceptReject Open 7 days · Hours vary by day · 25 years' experience [Office: 01279 216 215](tel:01279216215) | [Mobile: 07379 964569](tel:07379964569) [![J&Co Contractors logo](/assets/jandco-logo-DkXiFtbE.png)](/) Services Areas [About](/about/) [Our Work](/our-work/) [Blog](/blog/) [Reviews](/reviews/) [Contact](/contact/) [01279 216 215](tel:01279216215) [Free Quote](/contact/) 1. [Home](/) 2. [Building & Construction](/building-construction/) 3. [Extensions](/building-extensions/) 4. Single vs Double-Storey Extensions: How to Choose Guide · Extensions # Single vs Double-Storey Extensions: How to Choose Double-storey extensions cost more in absolute terms but cheaper per m² and add more value. Single-storey is faster, less disruptive, and often achievable under Permitted Development. Here's the honest comparison. Last updated: May 2026 · By Jamie Pocock Quick Answer **Choose single-storey if your priority is a kitchen-diner and the budget is £45,000–£100,000.** Choose double-storey if you also need an extra bedroom and the budget is £80,000–£160,000 — the per-m² cost drops by 20–30% because foundations and roof costs spread across two floors. Double-storey adds significantly more property value too: typically 18–25% versus 10–15% for single-storey on the same plot. ![Comparison of single-storey and double-storey rear extensions on Hertfordshire family homes](/assets/upload-009-DFap0EVo.jpeg) ## What each one delivers ### Single-storey rear extension One additional ground-floor room — almost always used as kitchen, dining and informal living combined into an open-plan space. Typical floor area 15–35m². Roof is usually flat (EPDM, GRP) or pitched with rooflights. Stays connected to the main house via knock-throughs from the existing kitchen and dining areas. ### Double-storey extension Two floors of additional space — ground floor as per single-storey above, plus an additional bedroom (typically with en-suite) on the first floor. Floor area usually 20–40m² per level, total 40–80m² added. Roof typically pitched to match the existing house. Significant impact on rear elevation appearance. ## Cost comparison — the per-m² advantage Single-storey extension: £2,200–£3,200/m² typical for standard build. Double-storey: £1,800–£2,500/m² typical because the foundations, roof, scaffold and project mobilisation costs are shared across twice the floor area. For example, on the same plot a 25m² single-storey costs £55,000–£80,000 (~£2,500/m²); a 50m² double-storey costs £100,000–£140,000 (~£2,200/m²) — twice the floor area for less than twice the cost. Full pricing detail in our [extension cost guide](/guides/how-much-does-a-house-extension-cost/). ## Property value uplift Single-storey extensions in Hertfordshire/Essex typically add 10–15% to property value. Double-storey extensions typically add 18–25%. The extra bedroom changes the home's "category" on the property market — a 3-bed becomes a 4-bed, which moves it into a different price bracket entirely. The value uplift on going from 4 to 5 beds is usually less dramatic than 3 to 4, so consider where your extension lands you in the local property hierarchy. ## Planning permission Single-storey rear extensions often fall under Permitted Development (4m projection on detached, 3m on semi/terrace; 4m height; volume limits apply). Larger Prior Approval extensions to 8m projection are also possible. Double-storey extensions have stricter PD limits — 3m projection maximum, must not exceed existing roof line, 7m minimum from rear boundary. Many double-storey extensions exceed PD and need full planning permission (£258 fee, 8–12 week determination). ## Direct comparison Factor Single-storey Double-storey Cost (typical, 2026) £45k–£100k £80k–£160k Cost per m² £2,200–£3,200 £1,800–£2,500 Build time 14–18 weeks 16–22 weeks Floor area added 15–35 m² 40–80 m² Adds bedroom? No Yes (typically + en-suite) Property value uplift 10–15% 18–25% Planning Often PD Often planning Disruption Moderate Significant Family in residence? Usually yes Often move out final weeks Party Wall Act Sometimes Almost always ## Other things that swing the decision **Garden footprint loss.** Both eat into garden space, but the same square-metres-of-extension applied to a double-storey loses half the garden of an equivalent single-storey. If garden space matters, double-storey gives more house per garden lost. **Rear elevation appearance.** Double-storey extensions visibly change the back of the house. Single-storey extensions tuck under the existing first-floor windows. Conservation areas and properties on prominent street corners often face more planning scrutiny on double-storey schemes. **First-floor layout impact.** Double-storey extensions usually require reconfiguring the existing first-floor layout — adding the new bedroom often involves a small landing extension, sometimes moving an existing bedroom door. Architect attention here is critical. **Loft conversion alternative.** If your goal is "extra bedroom plus better kitchen", consider single-storey extension plus [loft conversion](/loft-conversions/) rather than double-storey. Cost can be similar (£90,000–£150,000 combined) and you get three space gains rather than two: ground-floor kitchen, loft bedroom, plus the original first-floor bedroom kept intact. **Side return as alternative on terraces.** On Victorian and Edwardian terraces, side returns deliver kitchen-extension benefits at lower cost than full single-storey rear extensions. Worth comparing all three: side return, single-storey rear, side return + rear (wrap-around). **Mortgage and re-mortgage.** Double-storey extensions adding a bedroom typically support stronger re-mortgage valuations because the property moves into a higher local price bracket. Discuss with your lender or broker before committing — releasing equity can fund a meaningful share of the cost. ![Recently completed roofing project by J&Co Contractors in Hertfordshire](/assets/wa-435-169-BMBPQKLs.jpeg) About the Author ## Jamie Pocock — Owner & Lead Contractor Jamie has 25 years' hands-on experience in roofing and building across Hertfordshire and Essex. He runs every J&Co Contractors project personally — from quote to completion — and writes these guides from real on-the-tools knowledge of what works, what doesn't, and what costs what in 2026. - 25 years' hands-on roofing and building experience - CRC Certified Roofer — self-certifies under Building Regs - SafeContractor approved - Written completion sign-off on every job FAQs ## Frequently asked questions ### Is double-storey always better value than single-storey? ### Will double-storey planning be harder to get? ### Can I extend single-storey now and add a second floor later? ### How much disruption does each cause? ### Do I need separate quotes for each option? ### What's most popular in Hertfordshire and Essex? Related Guides [How much does a house extension cost?](/guides/how-much-does-a-house-extension-cost/) [Dormer vs Velux loft conversions](/guides/dormer-vs-velux-loft-conversions/) [Back to Extensions](/building-extensions/) ## Considering an extension in 2026? We'll quote both single and double-storey options where they're both viable on your plot — line-by-line comparison so you can choose with full information. Owner-led delivery, written fixed price. [See our extensions service](/building-extensions/) [01279 216 215](tel:01279216215) Page last updated: May 2026 · J&Co Builders Ltd · 1 Ugley Hall Cottages, Bishop's Stortford CM22 6JB ![J&Co Contractors](/assets/jandco-logo-DkXiFtbE.png) Owner-led roofing and building contractors covering Bishop's Stortford, Hertfordshire and Essex. 25 years of hands-on trade experience. Open seven days. 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