Cost guides · 5 min read
How much does a double storey extension cost?
A double storey extension is the best value big move in home extending: you pay for one set of foundations and one roof, and get two floors of space between them. On family homes across Enfield, Cheshunt and Barnet it typically adds a proper kitchen diner downstairs and a bedroom with en-suite above.
What a double storey extension costs
| Project | Indicative cost (2026) |
|---|---|
| Modest two-storey rear (~30 m² total) | £65,000 to £90,000 |
| Full-width two-storey rear (~45 m² total) | £90,000 to £130,000 |
| Two-storey side extension with garage under | £90,000 to £140,000+ |
Per square metre, expect £2,500 to £2,900, usually better value than a single storey at the same finish because the expensive parts, groundworks and roof, are shared across two floors. Kitchens and bathrooms are on top of the build cost as always.
Planning: the honest position
Double storey extensions get more planning scrutiny than single storey ones. Rear projections are limited (typically 3 metres under permitted development, and only outside conservation areas, with distance-to-boundary rules), and side extensions near a neighbour usually need a full application. It is normal, not a blocker: we design to what your street and council will support and manage the application.
Living through the build
- Most families stay in the house: the new structure goes up before the old wall opens.
- Expect roughly 16 to 22 weeks on site depending on size and spec.
- Scaffolding and deliveries need planning on tighter streets, which we sort early.
Frequently asked questions
Is a double storey extension worth it over a single storey?+
If you need a bedroom as well as living space, almost always. The cost per square metre is lower and the value added, an extra bedroom plus bathroom, is exactly what buyers in this area pay for.
Do I need planning permission for a double storey extension?+
Often yes, especially side extensions and anything in a conservation area. Some modest rear projections qualify as permitted development. We check your address and handle the application either way.
How long does it take?+
Typically 16 to 22 weeks on site once design and approvals are done, and we give you the programme with the quotation.