County Down
Flat-roof rear extensions in County Down
Warm flat roofs with lanterns, parapets and long-life membranes. Across County Down we handle the whole rear extension: survey, drawings, the planning route, building control and the build. Towns we cover here include Bangor, Castlereagh and Newtownards.
Flat roofs are the usual choice for rear extensions because they stay below first-floor windows and take a lantern neatly. Semis and detached houses are typical of County Down, and many have room for a rear extension within Northern Ireland's permitted development limits.
How much does a flat-roof rear extension cost in County Down?
In County Down, our guide for a flat-roof rear extension is £1,650–£2,700 per square metre including VAT for a standard specification. Northern Ireland prices are the lowest in our range.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £20,000–£32,500 |
| 4 m wide × 5 m deep (20 m²) | £33,000–£54,000 |
| 4 m wide × 6 m deep (24 m²) | £39,500–£64,500 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission in County Down?
In Northern Ireland the Planning (General Permitted Development) Order (Northern Ireland) 2015 allows a single-storey rear extension of up to 3 metres on an attached house or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary. Building control approval from the council is still required.
Insulation and glazing follow Technical Booklet F1 in Northern Ireland, checked by council building control.
Conservation areas, Areas of Outstanding Natural Beauty and listed buildings restrict permitted development in Northern Ireland.
Where in County Down 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 County Down?
We cover 8 towns and districts in County Down, including Bangor, Castlereagh and Newtownards.
Who builds the extension?
Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.