Design and Build Extensions in Brentwood, Chelmsford & Across Essex — Town-by-Town Guide

Kirkwood provides design and build extensions and loft conversions across Essex — covering Brentwood, Chelmsford, Billericay, Basildon, Wickford, Rayleigh, Leigh-on-Sea, Southend-on-Sea, and Hornchurch. Each of these towns has its own council, its own common house types, and its own local planning quirks. This guide covers each one individually, with the local detail that actually matters if you’re planning an extension or loft conversion in that specific area.

Design and Build Extensions by Town

Click through to the town that applies to you.

Brentwood

Kirkwood covers Brentwood as one of its core service areas, working across the town and the surrounding villages, including Shenfield, Hutton, and Ingatestone.

Council and planning: Brentwood Borough Council has a detailed design guidance framework that affects extensions in conservation areas, particularly in Shenfield, Warley, Ingrave, and South Weald. Extensions in these areas need to demonstrate they respect the character of the surrounding streetscape, which usually means a full planning application rather than permitted development.

House types: Brentwood has a mix of large detached homes, particularly around Hutton Mount and Shenfield, alongside 1930s and post-war semi-detached properties closer to the town centre. Detached homes with hip roofs are common, making hip-to-gable loft conversions a popular choice where owners want to maximise the extra floor space.

Common projects: Kirkwood regularly completes rear extensions and hip-to-gable loft conversions in Brentwood, along with kitchen extensions on the town’s larger family homes.

Local guide: See our full Brentwood planning permission guide for details on conservation areas and application timescales.

Billericay

Council: Basildon Council

Kirkwood covers Billericay as one of its strongest-performing areas. House extensions in Billericay are consistently one of the highest-demand searches Kirkwood sees, and the town has a strong track record of completed projects.

Council and planning: Billericay falls under Basildon Council for planning purposes, despite being a distinct town in its own right. Billericay Town Centre and Great Burstead have designated conservation areas with specific boundaries confirmed by Basildon Council always worth checking if your property is close to the historic centre.

House types: Billericay has a high proportion of semi-detached homes, many built in the 1960s and 1970s, alongside detached properties on the town’s more established roads. Hip-to-gable loft conversions are a popular choice here, particularly on the semis where a hipped roof limits usable space under a standard dormer alone.

Common projects: Rear extensions and hip-to-gable loft conversions are the two most common project types Kirkwood completes in Billericay.

Local guide: For cost details specific to the area, see our loft conversion cost Essex guide, which includes a dedicated Billericay section.

Chelmsford

Council: Chelmsford City Council

Kirkwood covers Chelmsford and the surrounding areas, including Springfield, Writtle, Broomfield, and Great Baddow. Homeowners searching for home design in Chelmsford or design and build Chelmsford will find Kirkwood covers the whole city.

Council and planning: Chelmsford City Council is the planning authority for the city and applies national permitted development rules consistently. The city has a significant number of designated conservation areas, 26 in total, where permitted development rights are more restricted, so checking your specific address matters before committing to a design.

House types: Chelmsford has a large number of 1970s and 1980s semi-detached homes across estates in Springfield and Broomfield, alongside Victorian terraces closer to the city centre. The 1970s and 1980s semis convert particularly well; their roof structures suit dormer loft conversions, and their kitchen layouts are strong candidates for a rear extension that opens up the ground floor.

Common projects: High demand in Chelmsford for dormer loft conversions and kitchen extensions, reflecting the housing stock across the city’s estates.

Local guide: See our full Chelmsford planning permission guide and our guide to planning permission for house extensions in Chelmsford.

Wickford

Council: Basildon Council

Kirkwood covers Wickford as our home town; it’s where we’re based, and loft conversions in Wickford are one of the highest-demand searches we see, reflecting strong local awareness of the service.

Council and planning: Wickford falls under Basildon Council for planning purposes. Most residential streets in Wickford are straightforward permitted development cases, and access for scaffolding and deliveries is generally good across the town’s estates, which helps keep build programmes on schedule.

House types: Wickford is predominantly post-war semi-detached and terraced housing, exactly the type of property that suits a rear dormer loft conversion well. Dormer conversions are consistently the most popular choice among Wickford homeowners.

Common projects: Dormer loft conversions are the most requested project in Wickford, alongside single-storey rear extensions. Anyone searching for builders in Wickford will find Kirkwood is based locally, not travelling in from elsewhere.

Local guide: See our dormer loft conversion cost guide for detailed 2026 pricing.

Basildon

Council: Basildon Council

Kirkwood covers Basildon and the surrounding estates, working across the town’s residential areas built from the 1950s onward.

Council and planning: Basildon Council is the planning authority for Basildon and processes most householder applications within the standard 8-week window. Basildon town centre has a designated conservation area; outside that, the majority of residential streets are straightforward permitted development cases.

House types: Basildon has large estates of 1960s and 1970s housing stock, built as part of the original Basildon New Town development. These properties generally have consistent roof structures and good ridge heights, making them well suited to loft conversions. Structural alterations removing internal walls to open up ground floor layouts are a common request alongside extensions on this housing stock, similar to the pattern seen on comparable 1970s estates in Chelmsford.

Common projects: High demand for both rear extensions and dormer loft conversions across Basildon’s estates.

Local guide: See our guide to planning applications with Basildon Council for local detail.

Rayleigh

Council: Rochford District Council

Kirkwood covers Rayleigh as part of our core service area. Loft conversions in Rayleigh are a strong area of demand, and we’ve completed projects across the town’s residential estates.

Council and planning: Planning applications in Rayleigh go to Rochford District Council. Rayleigh’s historic town centre has a conservation area, but the majority of the residential suburbs are straightforward permitted development cases.

House types: Rayleigh has a high proportion of 1970s semi-detached homes, similar in profile to parts of Chelmsford and Basildon. These properties are well suited to both dormer loft conversions and single-storey rear extensions.

Common projects: Extensions and loft conversions are both common in Rayleigh, with demand fairly evenly split between the two depending on whether homeowners need an extra bedroom or more ground-floor living space.

Local guide: See our loft conversion cost Essex guide for Rayleigh-specific figures.

Leigh-on-Sea

Council: Southend-on-Sea City Council

Kirkwood covers Leigh-on-Sea as part of our Southend-on-Sea coverage, one of the most desirable residential areas in South Essex, with property values to match.

Council and planning: Leigh-on-Sea sits within Southend-on-Sea City Council’s jurisdiction for all planning matters, with a local Leigh-on-Sea Town Council handling parish-level community matters only. Leigh has multiple designated conservation areas, including Leigh Old Town, Leigh, and Leigh Cliff, and Leigh Old Town has an Article 4 Direction removing certain permitted development rights, including roof alterations. Always check your property’s status before commissioning drawings here.

House types: Leigh-on-Sea has a mix of Edwardian semis, 1930s detached homes, and period coastal properties, particularly closer to Old Leigh and the seafront. Its coastal location and period housing stock mean loft conversions and roof work often need extra care around design and materials to satisfy conservation area requirements.

Common projects: Loft conversions and rear extensions are both common, along with conservatory roof replacement, a strong area of demand for older coastal properties in Leigh, where original conservatories are reaching the end of their working life.

Local guide: See our loft conversion cost Essex guide for a dedicated Leigh-on-Sea section.

Southend-on-Sea

Council: Southend-on-Sea City Council

Kirkwood covers Southend-on-Sea in full house extensions. Southend is a strong area of demand, and we work across the city’s diverse range of housing stock.

Council and planning: Southend-on-Sea City Council has several conservation areas, including Eastern Esplanade, Crowstone in Westcliff-on-Sea, Prittlewell, and Milton. Undercliff Gardens also has an Article 4 Direction protecting views from a public footpath. Checking your address against the City Council’s conservation area map is worthwhile before committing to a design.

House types: Southend covers a wide range of housing, from period terraces and Edwardian properties close to the seafront, post-war semis, and detached homes further inland in Thorpe Bay and Shoeburyness. Properties near the seafront and in Westcliff-on-Sea can have more complex roof structures and tighter access, while homes in Thorpe Bay and Shoeburyness tend to be more straightforward to extend.

Common projects: Rear extensions and loft conversions across the city’s varied housing stock, with kitchen extensions particularly popular on the post-war semis inland from the seafront.

Local guide: See our loft conversion cost Essex guide for a Southend-specific breakdown.

Hornchurch

Council: London Borough of Havering

Kirkwood covers Hornchurch as part of our extended service area. Loft extension Hornchurch is a search we see regularly, reflecting demand right on the Essex border.

Council and planning: Hornchurch sits within the London Borough of Havering, not an Essex authority worth noting, since it sits right on the Essex border and is often searched for alongside Essex towns. Havering applies the same national permitted development framework, but has conservation areas and Article 4 Directions in certain streets, so checking your property’s status matters here as much as anywhere else.

House types: Hornchurch has a mix of 1930s semis and larger detached homes, well suited to loft conversions and rear extensions alike. Being closer to London, build costs here run slightly higher than in mid-Essex towns, reflecting local labour rates.

Common projects: Loft conversions, particularly dormer conversions, are a strong area of demand in Hornchurch, alongside rear extensions on the borough’s larger semis and detached properties.

Local guide: See our loft conversion cost Essex guide for Hornchurch-specific pricing.

Get in touch

Whichever town you’re in, Kirkwood handles design, planning, and build as one service.

Frequently Asked Questions

Does Kirkwood cover my area?

Kirkwood covers Brentwood, Chelmsford, Billericay, Basildon, Wickford, Rayleigh, Leigh-on-Sea, Southend-on-Sea, and Hornchurch, along with the surrounding towns and villages across Essex. Kirkwood’s base is in Wickford. Get in touch, and we’ll confirm coverage for your specific address.

Do planning rules differ between Essex towns?

Yes, in practice. While permitted development rules are set nationally and apply the same way everywhere, each town has its own council with its own conservation areas, Article 4 Directions, and processing timescales. Brentwood, Chelmsford, Basildon, Rochford, and Southend-on-Sea each have different conservation area boundaries and, in Havering’s case (covering Hornchurch), a different planning authority entirely. Kirkwood checks the specific requirements for your address as part of every free consultation.

Do you do both the design and the build?

Yes. Kirkwood is a design and build company; one team handles the design drawings, planning permission or permitted development assessment, building regulations, and the physical construction. There is no handoff to a separate contractor at any stage.

How much does a design and build extension cost in Essex?

A single-storey rear extension typically costs £35,000 to £65,000 in Essex, including design, structural engineering, and the full build. Costs vary by town; areas closer to London, such as Hornchurch and Brentwood, tend to sit at the higher end. See our house extension costs guide for a full breakdown by extension type.

How long does a design and build extension take in Essex?

A single-storey rear extension typically takes 6 to 9 months from first enquiry to completion, including design, approvals, and the build. A double-storey extension takes 10 to 14 months. Timescales can vary slightly by council; some Essex authorities process applications faster than others, but the overall range holds fairly consistently across the towns Kirkwood covers.

What types of projects does Kirkwood design and build?

House extensions single-storey, double-storey, side return, and kitchen extensions and loft conversions, including dormer, Velux, and hip-to-gable types. Kirkwood also completes garage conversions and conservatory roof replacements across Essex, depending on the property and the town.

Ready to start your project?

Get a free, no-obligation quote from Kirkwood covering every town in this guide.

Jamie Lindsay is the founder of Kirkwood Build and has over 15 years of experience in residential construction, architectural design, and home extensions across Essex. He specialises in helping homeowners navigate the design, planning, and building process, sharing expert advice on extensions, renovations, and property improvements through the Kirkwood Build blog.