Hertfordshire
Rear extensions in Welwyn Garden City
Rear extensions in Welwyn Garden City: single-storey and two-storey extensions, side returns, wraparounds and glass-led designs, planned around Victorian terraces and 1930s semis and the English rules.
Welwyn Garden City is in Hertfordshire, with postcode districts including AL7 and AL8. The nearest places we also cover are Hatfield (2.8 miles) and Codicote (3.6 miles).
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Rear extensions we build in Welwyn Garden City
- Single-storey rear extensions
- Two-storey rear extensions
- Kitchen-diner rear extensions
- Side return extensions
- Wraparound extensions
- Glazed and glass-box rear extensions
- Rear extensions for terraced houses
- Rear extensions for semi-detached houses
- Rear extensions for bungalows
- Rear extension plans and planning applications
Also available across Hertfordshire:
- Rear extensions for detached houses
- Flat-roof rear extensions
- Pitched and lean-to roof rear extensions
- Knocking through to a rear extension
- Roof lanterns and rooflights for rear extensions
- Permitted development rear extensions
- Larger home extension prior approval (England)
- Building Regulations for rear extensions
Rear extension prices in Welwyn Garden City
East of England prices run slightly above our West Midlands baseline; clay soils near trees are the main foundation variable.
| Example | Guide inc VAT |
|---|---|
| Single-storey, 3 m × 4 m (12 m²) | £24,000–£39,500 |
| Single-storey, 4 m × 6 m (24 m²) | £48,500–£79,000 |
| Two-storey, 3 m × 5 m footprint (30 m²) | £57,000–£86,000 |
| Side return, about 14 m² | £34,000–£56,500 |
| Wraparound, about 25 m² | £58,500–£95,500 |
What are homes in Welwyn Garden City like to extend?
Welwyn Garden City mixes Victorian terraces with 1930s semis, so both side returns and full-width kitchen extensions suit houses here.
Planning rules for Welwyn Garden City
In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.
England also has the larger home extension route: a single-storey rear extension of up to 6 metres on an attached house or 8 metres on a detached house, after prior approval from the council. The council notifies your neighbours and has 42 days to decide; the fee is £249 (£310 for applications made from 8 December 2026). The route is not available on designated land such as conservation areas.
Planning and Building Regulations are separate in England: even a permitted development extension is inspected for foundations, drainage, structure, insulation, fire safety and ventilation, through the council or a registered building control approver, ending with a completion certificate.
Nearby towns
FAQ
Questions people ask
How much is a rear extension in Welwyn Garden City?
A 3 m × 4 m single-storey rear extension is about £24,000–£39,500 including VAT at our East of England guide rates; the written price follows a survey.
Do I need planning permission in Welwyn Garden City?
Often not for a single-storey rear extension of up to 3 metres (4 metres on a detached house) under permitted development, or up to 6 or 8 metres with prior approval, unless the house is in a conservation area or its rights have been removed.
Is the site visit in Welwyn Garden City free?
Yes, with no obligation.
Do I need a party wall agreement?
In England, usually yes if the extension is on or near a shared boundary or the foundations are close to a neighbour's building. We serve the notices.