Home Extensions Kent: The Complete 2026 Guide to Adding Space, Value and Quality to Your Property

The moment you start thinking seriously about a home extension is usually the same moment you realise just how much you don't know about it.

Planning permission or permitted development? Steel frame or structural brickwork? Single storey or two storey? How long will it take? How much disruption? And — the question nobody wants to get wrong — how much is this actually going to cost?

This guide answers all of it. Honestly, specifically, and with the genuine detail that makes the difference between walking into a contractor conversation prepared or getting sold something you didn't fully understand.

Marshall Brickwork & Construction has been delivering home extensions across Kent and Greater London for over 15 years — from modest single-storey kitchen extensions on Rochester terraces through to substantial two-storey additions on larger Medway and Maidstone properties. The knowledge in this guide comes from that track record, not from generalisation.

Why Extend Rather Than Move?

The calculation that leads most Kent homeowners to extend rather than move is increasingly compelling in 2026. Here's the honest maths.

Moving from a three-bedroom semi in the Medway towns to a four-bedroom equivalent — assuming you can find one in the same area and school catchment — involves stamp duty on both the purchase and the loss on the sale, solicitor fees, estate agent commission, removal costs, and the disruption of the process itself. In Kent's current market, that total friction cost easily reaches £25,000–£40,000 before you've made any improvement to your living space.

A well-executed single-storey rear extension on the same property — adding a kitchen-diner of 20–25m² — costs £35,000–£55,000 and delivers two things simultaneously: the additional space you were moving to achieve, and a meaningful increase in the property's market value. The disruption is significant but finite, you stay in the neighbourhood you've chosen, and the financial case is often compelling.

The extension isn't always the right answer. But for the majority of Kent homeowners who've outgrown their current layout without wanting to leave their location, it usually is.

Types of Home Extension: What's Available and What Each Delivers

Single-Storey Rear Extensions

The most commonly commissioned extension type in Kent, and for good reason — they deliver significant additional space for a relatively contained budget, they typically fall within permitted development rights (avoiding the planning process entirely), and they can transform how a home functions without altering its character from the street.

The typical brief is a kitchen-diner that opens directly into the garden — a single space combining what were previously separate and often small kitchen, dining room, and sometimes utility areas into one generous, light-filled room that becomes the heart of the house. It's the extension that changes how a family lives more fundamentally than any other type.

What a single-storey rear extension involves: Excavation and foundation construction (often the most technically demanding element, particularly on clay soils). Steel or timber beam structure for the roof and any structural openings. External brickwork walls in facing brick that matches the existing property. Roof — flat roof with membrane or pitched roof with tiles, depending on design and planning requirements. Glazing — large sliding or bifold doors opening to the garden are the most popular choice. Internal first fix (electrics, plumbing, underfloor heating if specified), insulation, internal walls, plastering, and finishing.

Typical size: 15–30m² is the most common range. Above 8 metres depth from the rear wall (or 6 metres for terraced properties) requires planning permission rather than permitted development.

Two-Storey Extensions

A two-storey extension adds space at both ground floor and first floor levels simultaneously, making it the most cost-effective way to add square footage when measured per metre added — because the foundation, roof, and scaffold costs are shared across two storeys.

The challenge is that two-storey extensions almost always require full planning permission (they affect the property's appearance from multiple elevations, often including the street), and the design needs more careful thought to ensure the extension looks intentional rather than added on.

When done well — matching brickwork, matching window styles, appropriate roof pitch — a two-storey extension is essentially invisible as an addition. It looks like part of the original house. This is the standard to aim for.

Typical applications: Additional bedroom and bathroom above a kitchen extension. Master suite with en-suite above a living room extension. Home office above a utility or garage.

Side Return Extensions

Many Victorian and Edwardian terraces and semis in Kent — particularly in Rochester, Chatham, and Maidstone — have a narrow passageway running along the side of the house between the main structure and the boundary. Infilling this side return creates surprisingly valuable additional floor space at ground level, typically adding 2–5m² that, when combined with the existing kitchen or dining room, can dramatically improve the layout.

Side return extensions are often combined with rear extensions in an L-shape configuration to maximise the single planning permission or permitted development allowance.

Garage Conversions

A garage conversion isn't technically an extension — it uses existing space rather than adding new square footage — but it achieves a similar result at significantly lower cost. Converting an attached garage into a habitable room (bedroom, office, gym, utility room) typically costs £15,000–£25,000 and often falls within permitted development rights.

The structural implications are usually limited: the garage floor needs insulating and levelling, the door opening needs to be replaced with a window and wall or a bifold door arrangement, the roof needs insulation, and services (power, heating) need extending into the space. It's the lowest-cost route to meaningful additional living space.

Loft Conversions

Converting an existing loft into a usable room — bedroom, bathroom, office — is one of the highest-return home improvements available, because it uses dead space within the existing building envelope without extending the footprint at all.

The feasibility depends on the roof pitch and the available head height. Most properties with a roof pitch of 30 degrees or more have sufficient height for a workable conversion. The two main structural approaches are dormer conversions (adding a box-like extension to the rear slope of the roof to increase headroom) and hip-to-gable conversions (relevant to semi-detached properties where the side hip slope can be replaced with a vertical gable wall to increase usable width).

Planning Permission: What You Need to Know Before You Start

Getting the planning question right before you commission any design work is one of the most important steps in the extension process. Getting it wrong costs money in either direction — commissioning full planning drawings for something that's permitted development wastes money on unnecessary work; starting building without permission when it's required creates enforcement risk that can be very expensive to resolve.

Permitted Development Rights

Under England's permitted development (PD) rules, many common extension types can be built without formal planning permission — subject to size limits, design criteria, and location conditions. The key rules for residential extensions in England in 2026:

Single-storey rear extensions: Can extend up to 8 metres from the original rear wall for detached houses, or 6 metres for semi-detached and terraced properties, without planning permission — subject to the extension not exceeding 4 metres in height and the roof not being higher than the existing roof.

Side extensions: Cannot extend beyond half the width of the original house. Cannot be higher than the existing eaves. For a terraced house, side extensions are not permitted development.

Two-storey extensions: Two-storey extensions to the rear are permitted development up to 3 metres depth from the rear wall, subject to height restrictions. Two-storey extensions to the side generally require planning permission.

Roof extensions and dormers: Rear dormers are permitted development within specific size limits. Front dormers require planning permission in most cases.

Important exceptions: Permitted development rights do not apply to flats or maisonettes. Properties in conservation areas, National Parks, or Areas of Outstanding Natural Beauty have reduced or eliminated permitted development rights. Listed buildings require listed building consent for any extension.

Kent has numerous conservation areas — Rochester, Faversham, parts of Maidstone, Tunbridge Wells, Canterbury, and many others — where PD rights are more restricted. Marshall Brickwork & Construction is familiar with the planning environment across the county and will advise on any consent requirements during the initial consultation.

The Prior Approval Process

Larger single-storey rear extensions (between 4–8 metres for detached, 4–6 metres for semi/terraced) technically fall within a prior approval process rather than full planning permission. You notify the council, neighbours are consulted, and if no objections are raised, work can proceed. This is simpler than full planning but still requires the formal notification step.

When Full Planning Permission Is Required

Full planning permission is required for two-storey extensions beyond the PD limits, for any extension in a conservation area that doesn't meet the specific criteria, for extensions to listed buildings (plus listed building consent), and for any extension that affects the character of the property in ways that PD rules don't cover.

Full planning applications take 8 weeks for a decision from the date of validation (or 13 weeks for major applications). The cost of the application itself is around £258 for a householder application in England. Architect drawings and planning support documentation add to this.

Home Extension Costs in Kent: Honest 2026 Figures

Extension costs are highly variable — more so than almost any other construction project type — because the scope, specification, and site-specific factors make a much bigger difference here than they do for, say, a standard driveway. These figures are honest guidance, not ballpark estimates designed to get you on the phone.

Single-Storey Rear Extension

Cost range: £30,000–£65,000 for a typical 20–25m² extension

The variation within this range reflects:

• Specification quality: A basic extension with standard finishes (ceramic floor tiles, painted walls, standard glazing) is at the lower end. A premium specification (large-format porcelain, bespoke bifold doors, underfloor heating, high-end finishes throughout) is at the upper end.
• Structural complexity: Extensions on flat sites with accessible ground are cheaper than those on sloping sites, with rock beneath the surface, or with existing drainage that needs diverting.
• Glazing choices: Bifold doors or large sliding doors for garden access add £3,000–£8,000 depending on width and specification. Rooflights add further.
• Roof design: A flat roof is typically less expensive than a pitched roof. A lantern or structural glass roof significantly more expensive.

Typical cost breakdown for a 20m² single-storey rear extension:

• Groundworks and foundations: £5,000–£10,000
• Structural frame and walls (brickwork): £8,000–£15,000
• Roof structure and waterproofing: £4,000–£8,000
• Windows and doors (including bifolds): £4,000–£10,000
• First fix (electrics, plumbing, heating): £3,000–£6,000
• Insulation: £1,500–£3,000
• Plastering, flooring, decoration: £4,000–£8,000
• Building regulations and structural engineer: £1,500–£3,000

Two-Storey Extension

Cost range: £55,000–£120,000 for a typical two-storey addition

The per-m² cost of a two-storey extension is typically lower than a single-storey (because foundations, scaffold, and roof are shared across two floors), but the total investment is higher because the scope is larger.

Garage Conversion

Cost range: £15,000–£28,000 depending on the extent of structural work and specification

The most cost-effective additional living space per pound spent, assuming the existing garage structure is sound.

Loft Conversion

Cost range: £35,000–£75,000 for a dormer conversion including bedroom and en-suite

Again highly variable based on the extent of dormer work, the specification of the bathroom, and whether structural alterations to the existing roof are required.

(THE DISPLAYED PRICES ARE ESTIMATIVE PER MARKET OFFERS AS OF TODAY)

The Structural Brickwork Question

This is where Marshall Brickwork & Construction's specific expertise becomes most relevant to extension work.

An extension's external walls are almost always specified in facing brick — and that brick must match the existing property. For newer properties, this is relatively straightforward: the manufacturer and range can often be identified from the property records or by contacting the builder. For older properties — particularly the Victorian and Edwardian housing stock across Rochester, Chatham, Maidstone, and much of Kent — matching is a craft skill. It involves assessing the brick colour, texture, size, and weathering characteristics, sourcing from reclamation yards where new manufacture won't match aged originals, and often blending new and reclaimed to achieve a convincing result from normal viewing distances.

The mortar specification is equally important for period properties. Using modern Portland cement mortar on an extension wall built against Victorian brickwork creates a visual and physical discontinuity that's difficult to resolve later. Matching the mortar colour, texture, and strength to the existing joints is part of what makes an extension look like it belongs.

Marshall's brickwork credentials — 200+ brickwork projects, 15 years of period property expertise, and the lime mortar knowledge that distinguishes genuine craft from competent approximation — make this the area where the company's involvement in an extension project adds the most specific value.

The Extension Process: From Idea to Handover

Understanding what happens at each stage helps you plan, budget, and avoid the most common sources of delay and cost overrun.

Stage 1: Initial consultation and feasibility (Week 1–2) The starting point is an honest conversation about what's possible, what's desirable, and what the approximate budget range looks like. Marshall's team visits the site, assesses the structural implications, discusses planning requirements, and gives an honest indication of scope and cost before any money is spent on drawings.

Stage 2: Design and planning (Weeks 2–10) If planning permission is required, architect drawings are commissioned and the application submitted. For permitted development, drawings are still needed for building regulations purposes but the planning wait is avoided. Structural engineering calculations are commissioned — required for building control sign-off and essential for getting the foundation and beam sizing right.

Stage 3: Building regulations approval Separate from planning permission, building regulations approval confirms that the design meets the technical standards for structure, insulation, fire safety, ventilation, and drainage. This can be handled by a building control body (local authority or approved inspector) either before work starts (full plans approval) or inspected at each stage during construction.

Stage 4: Groundworks and foundations (Weeks 1–3 on site) The most critical phase and the one most often underestimated. Foundation depth and type depend on the soil conditions — on Kent clay, strip foundations typically need to go significantly deeper than standard spec to reach stable ground. This is where unexpected costs most commonly arise: if the ground conditions are different from what was anticipated, the foundation scope changes.

Stage 5: Structure (Weeks 3–8 on site) Structural steel beams (for large openings), external brickwork, internal blockwork, roof structure, and weatherproofing. This is the stage where the extension takes visible shape.

Stage 6: First and second fix (Weeks 8–14 on site) Services installation (electrics, plumbing, underfloor heating), insulation, internal walls, windows and external doors, plastering, and the beginning of finishing trades.

Stage 7: Finishing and completion (Weeks 14–18 on site) Flooring, decoration, kitchen or bathroom fitting (if applicable), snagging, and the final building control inspection and completion certificate.

Total timeline: A typical single-storey rear extension takes 12–20 weeks on site from groundworks start to completion, plus the pre-construction period for design and planning.

What to Look for in an Extension Contractor in Kent

Extension projects have more places to go wrong than almost any other construction type. Here's the contractor evaluation framework that matters:

Proven structural brickwork capability. An extension's structure is brickwork. A contractor who subcontracts this to a separate bricklayer has less control over quality and programme than one whose core competency is brickwork. Marshall is a brickwork company that also builds extensions — not a general builder who happens to do brickwork.

Building regulations experience. The building control process requires the contractor to manage inspections at specific stages — foundation depth before concrete is poured, damp proof course position, structural beam installation, insulation specification. A contractor who isn't familiar with this process causes delays and potentially failed inspections.

Transparent pricing and change management. Extensions are more prone to scope changes than most projects — ground conditions, client design changes, services that weren't where the drawings said they'd be. How a contractor handles these is as important as the initial quote. Marshall's approach: any change that affects cost is communicated immediately, the implication is explained, and your approval is obtained before additional work proceeds.

Local knowledge. Kent's varied ground conditions — clay in the Medway towns and Sittingbourne, chalk in the North Downs, varying drainage conditions across the county — affect foundation specification significantly. A contractor who has worked extensively across Kent knows what to expect and how to specify correctly.

Frequently Asked Questions About Home Extensions in Kent

Do I need an architect? Not necessarily, but design drawings are required for both planning applications and building regulations. Some extension contractors (including Marshall) can recommend experienced local architects or architectural technicians who understand the planning environment in specific Kent areas. For simple single-storey extensions, an architectural technician is often sufficient and less expensive than a full architect.

Can I stay in the house during the extension build? Usually yes for single-storey rear extensions, though the kitchen and rear living areas will be significantly disrupted during groundworks and structure phases. Many families manage with a temporary kitchen setup. Two-storey extensions and loft conversions are generally easier to live around than single-storey rear extensions.

Does an extension add value? Yes, reliably — but the quantum depends on the property type, location, and local market. Single-storey kitchen extensions consistently return 15–25% of their cost as direct property value uplift in Kent's current market, plus the use value over the years of ownership. In the higher-value Kent markets (Sevenoaks, Tonbridge, Tunbridge Wells), the returns are at the upper end of this range.

What if my neighbours object to the extension? For permitted development projects, neighbours have no formal right to object (though they can raise issues during the prior approval process for larger PD extensions). For full planning applications, neighbour objections are considered by the planning authority alongside all other material planning considerations. A well-designed extension that complies with relevant policies will typically be approved regardless of individual objection.

Can you handle the whole project? Yes. Marshall Brickwork & Construction manages the complete extension scope — groundworks and foundations, structural brickwork, roof, external doors and windows, first fix services, insulation, plastering, and internal finishing. Single contractor, single timeline, single accountability. Subcontractors (specialist trades like electrics and plumbing) are managed directly by Marshall as the primary contractor.

Getting Started with Your Kent Extension Project

If you're planning a home extension — at whatever stage of the thinking process you're currently at — the most useful first step is an honest, no-pressure conversation about what's possible for your specific property and budget.

Marshall Brickwork & Construction offers free site visits and initial consultations for extension projects across Kent. The team covers Rochester, Medway towns, Sittingbourne and Swale, Maidstone, Tonbridge, Tunbridge Wells, Sevenoaks, Canterbury, Faversham, and into Greater London.

Phone: 07724 730872 Email: info@mbconstruction.group Contact: mbconstruction.group/contact/

Explore the full construction services range, browse completed projects including extension and new build work, and find in-depth guides on related services in the blog — including the complete brickwork guide, driveway cost guide, and patio construction guide.

The extension that adds the space your family needs, built properly, by people who know what they're doing — that's what Marshall delivers. Free quote. No obligation. Honest advice from day one.

Marshall Brickwork & Construction Ltd | 14 Poplar Road, Rochester, ME2 2NR | 07724 730872 | mbconstruction.group