Covering Welwyn Garden City
Welwyn Garden City is about 6 miles north-east of St Albans. We also cover Hatfield (3 miles to the south), Hertford and St Albans.
Homes in the East of England
The East of England has a large stock of post-war and modern estate housing alongside period homes in market towns, which makes garage conversions, single-storey extensions and loft conversions popular.
What goes into a double-storey extension?
A double-storey extension adds new rooms on both the ground and first floor in one build, typically a larger kitchen or living space downstairs and an extra bedroom or bathroom above. Because the roof and foundations are shared, the cost per square metre is usually lower than a single-storey extension.
- Structural engineer’s design and calculations
- Foundations, steelwork, brick and block walls, roof
- Windows, insulation, plastering, electrics and plumbing
How much should I budget for a double-storey extension?
Typical ranges for double-storey extensions. Ground conditions, access and specification move the final figure, which we fix in writing before work starts.
| Double-storey extensions | Guide price incl. VAT |
|---|---|
| Standard specification | £2,400 to £2,900 per m² |
| Good specification | £2,900 to £3,400 per m² |
| High specification | £3,400 to £3,850 per m² |
Do you need permission for a double-storey extension in Welwyn Garden City?
Projects in England go through two separate checks. Planning (or confirmation that the work is permitted development) comes from the district, borough or unitary council, and building regulations approval comes from the council’s building control team or a registered building control approver. Where work touches a shared wall or digs near a neighbour’s foundations, the Party Wall etc. Act 1996 applies.
Two-storey rear extensions can sometimes be permitted development in England (no more than 3 m deep, at least 7 m from the rear boundary, roof pitch to match), but most two-storey and all two-storey side extensions need householder planning permission.
What should Welwyn Garden City homeowners check first?
- Side extensions close to a boundary are often set back or stepped down so they do not create a terraced effect.
- The new roof is tied into the old one, so roof tiles and ridge details need to match.
What happens after I enquire?
- Start with a conversation. A short call or the online form is enough for us to understand what you want to build.
- We visit and measure. A surveyor checks the house, the boundaries and the ground, and discusses what is realistic.
- Drawings, approvals, written quote. We prepare the design, apply for the approvals it needs, and give you a fixed price in writing.
- Build and hand over. Our teams build to the programme, building control inspects, and you get the completion paperwork at the end.
Your questions answered
How much does a two-storey extension cost?
Typically about £2,400 to £3,850 per square metre of new floor area including VAT. A 40 m² extension across two floors is often around £100,000 to £150,000 depending on specification.
How long does a two-storey extension take?
Around 14 to 24 weeks on site, plus the planning period before that.
Who deals with the council for a project in Welwyn Garden City?
We do. We prepare the drawings, submit planning or permitted development paperwork if needed, and arrange building control inspections.
Other towns nearby
- Double-storey extensions in Hatfield
- Double-storey extensions in Hertford
- Double-storey extensions in St Albans
- Double-storey extensions in Harpenden
Learn more about double-storey extensions, or see every project we cover in Welwyn Garden City.