House Extensions in Kent: Planning, Cost and What to Expect (2026)
A practical guide to extending your home in Sittingbourne or across Kent — covering planning permission, building regulations, costs, and the trades involved.
A house extension is one of the most significant home improvement investments available to Kent homeowners — and one of the most complex to plan and execute. Done well, an extension adds substantial living space and long-term property value. Done poorly, it creates years of problems with damp, structural movement, and non-compliant building work that will surface when the property is sold. Understanding the process before you start is essential.
Do You Need Planning Permission?
Many single-storey rear extensions in Kent can be built under Permitted Development rights without a formal planning application, provided they meet specific size and siting criteria. The key limits for a detached house are a maximum depth of 8 metres from the original rear wall (4 metres for semi-detached and terraced properties), a maximum height of 4 metres, and no extension beyond the side elevation. Properties in Conservation Areas, Areas of Outstanding Natural Beauty, or those with Article 4 Directions have more restrictive rules. Sittingbourne town centre and parts of the Swale district have specific local policies — always check with Swale Borough Council before assuming Permitted Development applies.
Even if planning permission is not required, Building Regulations approval is always required for a house extension. This covers structural integrity, insulation, fire safety, ventilation, drainage, and electrical installation. Skipping Building Regulations is not an option — it creates an unregistered extension that will cause serious problems when you sell the property.
Typical Extension Costs in Kent (2026)
| Extension Type | Typical Cost Range | Notes |
|---|---|---|
| Single-storey rear (20 sq m) | £30,000 – £50,000 | Standard spec, plastered and decorated |
| Single-storey rear (30 sq m) | £45,000 – £75,000 | Larger kitchen-diner extension |
| Double-storey rear | £60,000 – £120,000 | Two floors, adds bedroom and living space |
| Side return extension | £25,000 – £50,000 | Common in Victorian terraces, widens kitchen |
| Loft conversion (dormer) | £35,000 – £60,000 | Adds bedroom and bathroom |
| Garage conversion | £10,000 – £25,000 | Insulation, flooring, electrics, plastering |
The Trades Involved in a House Extension
A house extension requires a builder or groundworker for foundations and structure, a bricklayer or timber frame specialist, a roofer, a plumber if the extension includes a bathroom or kitchen, an electrician for the new circuits and consumer unit upgrade, a plasterer, a tiler, a carpenter for doors and windows, and a decorator. The electrical element is always a notifiable Part P job — any new circuit added to serve an extension must be designed, installed, and certified by a registered electrician.
Kent Trade Solutions manages the electrical and air conditioning elements of extension projects, working alongside the main contractor to ensure the new space is correctly wired, certified, and — where required — fitted with a split-system air conditioning unit for year-round comfort. We also coordinate the other trade elements through our network of vetted Kent partners, providing a single point of contact for the full project.
How Long Does a House Extension Take?
| Extension Type | Typical Build Time |
|---|---|
| Single-storey rear (standard) | 10–16 weeks |
| Double-storey rear | 16–24 weeks |
| Side return | 8–14 weeks |
| Loft conversion | 8–12 weeks |
| Garage conversion | 4–6 weeks |
Finding the Right Team in Kent
The most common cause of extension projects going over budget and over time is poor coordination between trades. When each contractor is booked independently, gaps appear between them — the bricklayer finishes, but the roofer is not available for three weeks, and the whole project stalls. Using a single contractor or project manager who coordinates all trades and takes responsibility for the programme is the most effective way to keep a project on track. Kent Trade Solutions provides this coordination for the electrical, AC, and finishing trade elements of extension projects across Sittingbourne, Medway, Faversham, Maidstone, and Canterbury.
Kent Trade Solutions
NICEIC-registered Electrician & Refcom-certified AC Engineer, Sittingbourne, Kent
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