Single Storey Extensions in Essex - Design, Planning & Build
A single storey extension is one of the most cost-effective ways to add space to your home in Essex — without the disruption of moving. Whether you want a larger kitchen, an open-plan living area, or an extra room, Kirkwood handles everything from the first drawing through to the finished build. Prices start from £30,000 for a standard rear extension. Design, planning permission, structural engineering, and build are all managed by one team.
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SINGLE STOREY EXTENSION COSTS IN ESSEX – 2026 QUICK GUIDE
Rear extension: from £35,000
Side extension: from £30,000
Wraparound extension: from £60,000
Flat roof extension: from £30,000
Pitched roof extension: from £35,000
Garage conversion: from £15,000
All prices include design, structural engineering, planning, and build. Get a free quote to find out the cost for your specific home.
How Much Does a Single Storey Extension Cost in Essex?
The cost of a single storey extension in Essex depends on the type, size, and specification. Below are typical price ranges for 2026, including design, structural engineering, and build. These figures cover the most common extension types across Brentwood, Billericay, Chelmsford, Wickford, Basildon, and surrounding areas.
| Extension Type | Cost (Essex, 2026) | Build Time | Planning | Best For |
| Rear extension | £35,000 – £65,000 | 10–14 weeks | Often PD* | All house types |
| Side extension | £30,000 – £55,000 | 8–12 weeks | Often PD* | Detached/semi-detached |
| Wraparound extension | £60,000 – £120,000 | 14–20 weeks | Usually needed | Homes with side return |
| Flat roof extension | £30,000 – £60,000 | 8–12 weeks | Often PD* | Modern homes, tight plots |
| Pitched roof extension | £35,000 – £70,000 | 10–14 weeks | Often PD* | Period/traditional homes |
| Porch extension | £8,000 – £20,000 | 3–5 weeks | Rarely needed | All house types |
| Garage conversion | £15,000 – £35,000 | 4–8 weeks | Rarely needed | Homes with attached garage |
| Outbuilding / annex | £40,000 – £90,000 | 10–16 weeks | Sometimes | Larger plots |
WHAT IS AND IS NOT INCLUDED IN THESE PRICES
Included: Architectural design drawings, structural engineering calculations, planning or permitted development application, building regulations package, and the full build (groundworks, structure, roofing, insulation, plasterboard, first fix electrics and plumbing, staircase if applicable).
Not included: Decoration and painting, floor finishes, kitchen or bathroom fitting, fitted furniture. Budget an additional £5,000–£20,000 depending on specification.
Types of Single Storey Extension
Single storey extensions come in a variety of forms, each suited to different properties, budgets, and goals. Here is a practical guide to the most common options across Essex.
Rear Extensions
Side Extensions
Wraparound Extensions
Flat Roof Extensions
Pitched Roof Extensions
Porch Extensions
Garage Conversions
Outbuildings/Annex
Rear Single Storey Extensions
A rear single storey extension extends into your garden to create a larger kitchen, open-plan kitchen-diner, living area, or home office. It is the most popular extension type in Essex. Most rear extensions on terraced and semi-detached homes fall under permitted development — no planning application needed for extensions up to 3 metres (or 6 metres with prior approval under the Neighbour Consultation Scheme).
A rear extension is typically the most cost-effective way to add meaningful space to a home. The build is straightforward, disruption is mainly at the rear of the house, and the finished space can transform how a home functions day-to-day. In Essex, rear extensions are particularly popular in Billericay, Brentwood, Chelmsford, and Wickford where 1960s–1980s semi-detached homes often have good-sized gardens and limited ground floor living space.
Single Storey Side Extensions
A side extension uses the space beside your home — typically a side alleyway or the gap between your house and the boundary. It is well suited to semi-detached and detached properties where there is an unused strip of land to the side. Side extensions can create a utility room, home office, playroom, or an enlarged kitchen. They are also popular as a way to add a downstairs WC or to create a proper entrance lobby.
Side extensions often require more careful planning consideration than rear extensions, as they can affect the streetscene. Kirkwood’s team assesses planning risk as part of the initial free consultation, and in most cases we know before any drawings are done whether planning permission will be required.
Wraparound Extensions
A wraparound extension combines a rear and side extension into a single L-shaped structure, creating the largest possible ground floor footprint from a single storey build. They are particularly popular on period terraced homes with a side alleyway, and on semi-detached properties where a side extension is viable alongside a rear extension.
Wraparound extensions in Essex typically cost £60,000 to £120,000 depending on size and specification. They almost always require full planning permission because the combined scale exceeds permitted development limits. The result is a significantly transformed ground floor typically an open-plan kitchen, dining, and living area with real connection to the garden. Kirkwood has completed numerous wraparound extensions across Essex, including projects in Billericay, Leigh-on-Sea, and Brentwood.
Flat Roof Single Storey Extensions
Flat roof extensions are the most common form of single storey extension in Essex. They are cost-effective, quick to build, and their clean horizontal design allows them to fit naturally onto a wide range of homes. Modern flat roof extensions use high-quality roofing membranes — typically EPDM rubber or GRP fibreglass — which are durable, low-maintenance, and typically come with a 20-year guarantee.
Flat roofs allow for large roof lights (skylights), which are one of the most effective ways to bring natural light into the centre of a deep extension. A well-positioned rooflight can transform what might otherwise be a dark space into a bright, airy room.
Flat roof extension cost in Essex ranges from £30,000 to £60,000 for a standard single storey build in 2026. The roof covering itself costs £50 to £120 per square metre depending on material.
Pitched Roof Single Storey Extensions
A pitched roof extension uses a sloped roof, either matching the existing house or designed as a contrasting contemporary statement. Pitched roofs are often preferred by planning officers as they tend to integrate better with the existing property and the surrounding streetscene — particularly in conservation areas or on period homes.
The advantages of a pitched roof include better insulation performance, greater durability (no flat roof drainage to manage), and the possibility of vaulted ceilings inside the extension. A vaulted or cathedral ceiling in a single storey kitchen extension adds significant volume to the room without increasing the footprint.
Pitched roof extension costs in Essex are typically £35,000 to £70,000 for a standard single storey build in 2026. The additional roof structure costs slightly more than flat, but the visual result and planning reception are often worth it.
Porch Extensions
A porch extension creates a covered entrance at the front or side of your home. It provides a practical space for coats, shoes, and storage, and protects the front door from weather. Most small porches fall under permitted development and do not require planning permission, provided they remain within 3 square metres, are no higher than 3 metres, and are set back at least 2 metres from any boundary adjacent to a highway.
Porch extension costs in Essex range from £8,000 to £20,000 depending on size and materials. Brick-built porches at the higher end, timber or steel frame porches at the lower end.
Garage Conversions
A garage conversion is technically not an extension — it uses existing space rather than creating new footprint — but it is one of the most cost-effective ways to add a proper room to a home. Converting an attached garage into a bedroom, home office, gym, or playroom typically costs £15,000 to £35,000 in Essex, including insulation, plasterboard, electrics, and finishing.
Most garage conversions do not require planning permission, but building regulations approval is always required. Kirkwood handles the building regulations package as part of its complete service. Garage conversions are particularly popular in Chelmsford, Wickford, and Basildon where 1970s–1990s homes were commonly built with integral garages that are now rarely used for cars.
Outbuildings & Annex Extensions
An outbuilding or garden annexe can serve as a home office, gym, guest bedroom, or self-contained living space for a family member. Unlike traditional extensions, outbuildings can be either connected to the main house or positioned elsewhere in the garden. Many outbuildings fall under permitted development, though larger structures and those used for independent living often require planning permission.
Outbuilding and annexe costs in Essex range from £40,000 to £90,000 depending on size, specification, and whether services (electricity, plumbing, heating) are connected. Kirkwood assesses each outbuilding project individually and advises on the most practical and cost-effective approach.
Do You Need Planning Permission for a Single Storey Extension in Essex?
Most single storey rear extensions in Essex do not require planning permission. They proceed under permitted development rights — a set of rules that allow homeowners to make certain changes without a planning application, provided the work stays within defined limits.
Permitted Development — What Is Allowed
Under permitted development, you can typically build a single storey rear extension without planning permission if:
- The extension does not exceed 3 metres from the rear wall for terraced and semi-detached homes, or 4 metres for detached homes
- The roof height does not exceed 4 metres (pitched) or 3 metres (flat) at the highest point
- The extension does not extend beyond the side wall of the house
- The materials used are similar in appearance to the existing property
- The property is not in a conservation area, AONB, or listed
Under the Neighbour Consultation Scheme (also called Prior Approval), you can extend up to 6 metres for semi-detached and terraced homes, or 8 metres for detached homes, subject to neighbours being notified. The council has 42 days to object. If no objection is raised, the extension can proceed.
When Planning Permission Is Needed
Full planning permission is required for:
- Extensions that exceed permitted development size limits
- Side extensions on properties in conservation areas
- Wraparound extensions (which typically exceed PD limits due to combined size)
- Extensions on listed buildings
- Flats and maisonettes (permitted development does not apply)
- Properties where permitted development rights have been removed by a planning condition
Kirkwood assesses your planning position as part of the free initial consultation. In most cases we can tell you before any drawings are prepared whether you will need planning permission, and what the likely outcome will be.
LAWFUL DEVELOPMENT CERTIFICATE — ALWAYS WORTH GETTING
Even when planning permission is not required, Kirkwood recommends applying for a Lawful Development Certificate from your local council. This is a formal confirmation that your extension is lawful under permitted development.
Planning in Specific Essex Councils
Kirkwood regularly works with the following local planning authorities across Essex:
- Brentwood Borough Council — active planning authority with a design SPD. Extensions in conservation areas need careful handling.
- Chelmsford City Council — generally supportive of well-designed extensions. Online planning portal allows progress tracking.
- Basildon Council — covers Basildon, Billericay, and Wickford. Standard permitted development rules apply across the borough.
- Rochford District Council — covers Rayleigh, Hockley, and surrounding areas. Some Article 4 direction areas where permitted development is restricted.
- Castle Point Borough Council — covers Benfleet, Canvey Island, and Leigh-on-Sea. Coastal and conservation area policies in parts of the borough.
- Southend-on-Sea City Council — unitary authority. Urban density means planning officers pay close attention to neighbour impact.
How the Process Works — From Enquiry to Completion
Kirkwood manages the full process from first conversation to finished build. Here is what to expect at each stage.
Step 1 — Free consultation We meet at your property, assess the space, discuss what you want to achieve, and give you an honest cost estimate. No charge, no obligation. |
| Step 2 — Design drawings Our team prepares full architectural drawings and floor plans. You review and amend until you are happy. This typically takes 4–6 weeks. |
Step 3 — Planning / permitted development We handle the planning application or permitted development assessment and Lawful Development Certificate. Planning typically takes 8–10 weeks if required. |
| Step 4 — Building regulations Structural calculations and building regulations submission. This runs concurrently with planning. Approval typically takes 5–8 weeks. |
Step 5 — Build Groundworks, structure, roofing, first fix, plastering, and finishing. A standard single storey rear extension takes 10–14 weeks to build. |
| Step 6 — Completion and sign-off Building inspector sign-off, snagging, and handover. Your completion certificate is issued — important for when you sell the property. |
A typical single storey rear extension under permitted development takes 6 to 9 months from first call to completion. If planning permission is required, allow 10 to 12 months.
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Based in Brentwood, Essex, we were also introduced to builders and tradespeople through Kirkwood, and they were excellent—professional, respectful, and a pleasure to work with. If we ever take on another project, we wouldn’t hesitate to use them again.
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Single Storey Extensions Across Essex — Areas We Cover
Kirkwood provides single storey extension design and build services across Essex and parts of East London. Our team has completed projects in Brentwood, Billericay, Chelmsford, Wickford, Basildon, Rayleigh, Leigh-on-Sea, Southend-on-Sea, Hornchurch, Benfleet, Grays, Colchester, Braintree, Chigwell, and surrounding areas.
If you are unsure whether we cover your area, call 01268 944233 or use the quick quote tool — we will confirm within 24 hours.
Single Storey Extension — Frequently Asked Questions
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How much does a single storey extension cost in Essex?
A single storey rear extension in Essex costs between £35,000 and £65,000 in 2026, including design, structural engineering, and build. A small 3x3m extension starts from around £30,000. A larger 6x4m wraparound costs £75,000–£120,000. Get a free quote for your specific property.
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Do I need planning permission for a single storey extension in Essex?
Most single storey rear extensions do not need planning permission — they proceed under permitted development. Rear extensions up to 3 metres (semi/terrace) or 4 metres (detached) are typically permitted development. Kirkwood assesses your planning position for free before any drawings are prepared.
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What size single storey extension qualifies as permitted development?
For terraced and semi-detached homes: up to 3 metres to the rear, or up to 6 metres under the Neighbour Consultation Scheme. For detached homes: up to 4 metres, or up to 8 metres with prior approval. The roof must not exceed 4 metres (pitched) or 3 metres (flat). Kirkwood checks your specific PD position as part of the free consultation.
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How long does a single storey extension take?
From first call to completion: 6–9 months for an extension under permitted development. 10–12 months if planning permission is required. The build itself takes 10–14 weeks for a standard rear extension. Design, approvals, and building regulations take an additional 3–5 months running concurrently.
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What is the cheapest type of single storey extension?
A porch extension is the cheapest, from £8,000. For a full habitable room, a single storey rear extension is typically the most cost-effective starting from around £30,000–£35,000. Garage conversions are also good value at £15,000–£35,000 for a proper finished room.
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Does a single storey extension add value?
Yes, typically 5–15% depending on location and size. A well-designed open-plan kitchen extension adds the most value in Essex. In towns like Billericay and Brentwood where 4-bedroom homes command significantly more than 3-bedroom equivalents, adding a bedroom through an extension often delivers strong returns.
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What is the difference between flat roof and pitched roof extensions?
Flat roofs are more cost-effective and modern-looking. They are quicker to build and allow for large rooflights to bring in natural light. Pitched roofs match traditional homes better, are preferred by some planning officers, offer better insulation performance, and can have vaulted ceilings for extra volume. Kirkwood recommends the best option based on your property type and planning context.
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Can I build a wraparound extension under permitted development?
Rarely. A wraparound extension combines a rear and side extension, and the combined volume typically exceeds permitted development limits. Most wraparound projects require full planning permission. Kirkwood manages the planning application as part of the full service.
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How much does a flat roof extension cost per m2?
Flat roof extension costs in Essex range from £1,800 to £2,600 per m2 for the build element in 2026. The roof membrane itself costs £50–£120 per m2 depending on material. Design and structural engineering are fixed costs on top.
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Do I need a structural engineer for a single storey extension?
Yes. All extensions require structural engineering calculations to ensure the new structure, steelwork (where walls are removed), and foundations are correctly designed. Kirkwood includes structural engineering in its complete design and build service — there is no need to hire a separate structural engineer.
