Kent
Flat-roof rear extensions in Kent
Warm flat roofs with lanterns, parapets and long-life membranes. Rear extensions in Kent: we cover 31 towns including Maidstone, Gillingham and Chatham, with design, approvals and the build under one contract.
Flat roofs are the usual choice for rear extensions because they stay below first-floor windows and take a lantern neatly. Kent has a mix of Victorian terraces near the centre and larger Edwardian and inter-war houses further out. Clay soils across much of the South East mean deeper foundations near trees, which we plan for at the survey.
How much does a flat-roof rear extension cost in Kent?
In Kent, our guide for a flat-roof rear extension is £2,130–£3,470 per square metre including VAT for a standard specification. South East prices run above our West Midlands baseline, mainly on labour rates and clay-soil foundations.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £25,500–£41,500 |
| 4 m wide × 5 m deep (20 m²) | £42,500–£69,500 |
| 4 m wide × 6 m deep (24 m²) | £51,000–£83,500 |
We put a fixed price in writing once the design is agreed, and explain any provisional sums such as foundations.
Do you need planning permission in Kent?
English permitted development (Class A) allows a single-storey rear extension of 3 metres on a terraced or semi-detached house and 4 metres on a detached one, measured from the original house, with a maximum height of 4 metres and eaves of no more than 3 metres within 2 metres of a boundary.
New fabric must meet Approved Document L (2021 edition incorporating 2023 amendments): walls 0.18, roof 0.15 and floor 0.18 W/m²K, windows 1.4 W/m²K or Band B. Under the simple route, new windows, doors and rooflights should not exceed 25% of the extension floor area plus any openings removed; more glass is possible with a whole-house calculation.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent.
Where in Kent do we work?
FAQ
Questions people ask
How long does a flat roof last?
A well-built single-ply or GRP warm roof typically lasts 25 years or more.
Is a flat roof really flat?
No; it is built to falls so water drains to outlets or gutters.
Can I walk on it?
Not as a balcony without planning permission and a guarding design; it can be accessed for maintenance.
Do you cover all of Kent?
We cover 31 towns and districts in Kent, including Maidstone, Gillingham and Chatham.
Who builds the extension?
Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.