What is a double-storey extension?
A double-storey extension (also called a two-storey extension) adds rooms on both the ground and first floor in one build. It typically gives a larger kitchen or living space downstairs and an extra bedroom or bathroom above.
How much does a double-storey extension cost in Hailsham?
In Hailsham, a double-storey extension typically costs £1,850–£2,800 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £66,500–£101,000. That range is adjusted for the South East, where domestic building work typically costs around 12% above the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £46,000–£70,000 |
| Typical project (36 m²) | £66,500–£101,000 |
| Larger project (50 m²) | £92,500–£140,000 |
| Rate per m² | £1,850–£2,800 |
The biggest cost drivers are:
- Scaffolding and access to the rear
- Steel beams where walls are opened up
- Total floor area across both floors
- Roof design and how it joins the existing roof
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a double-storey extension in Hailsham?
Here is how the rules work for a double-storey extension in England. In England an extension of more than one storey can only be permitted development at the rear, no more than 3 metres deep and at least 7 metres from the rear boundary, with matching materials and any upper side windows obscure-glazed. Most double-storey extensions therefore go through a householder planning application.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
From survey to sign-off, the job normally involves:
- Building control sign-off
- Design drawings and planning application
- Electrics, heating, plumbing and plastering
- Foundations, drainage and scaffolding
- Structural engineer’s calculations
- Brick or block walls, floors and a roof tied into the house
How long does it take?
The build itself usually takes 14 to 20 weeks on site, after planning and building control approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Hailsham
Commuter towns across the South East have many 1930s and post-war semis that suit rear extensions and hip-to-gable loft conversions.
We work across Hailsham and neighbouring areas such as Eastbourne, Seaford and Bexhill-on-Sea. Postcodes we cover in Hailsham include BN27.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about double-storey extensions in Hailsham
How much does a double-storey extension cost in Hailsham?
In Hailsham, a double-storey extension typically costs £1,850–£2,800 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £66,500–£101,000. Your fixed price depends on the survey and drawings.
How long does a double-storey extension take in Hailsham?
Typically 14 to 20 weeks on site, after planning and building control approval. Design and approvals beforehand usually take 3 to 4 months.
Does a double-storey extension need planning permission?
Usually. In England a two-storey rear extension can only be permitted development if it is no more than 3 metres deep and at least 7 metres from the rear boundary, and side extensions over one storey always need permission. In practice most are approved through a planning application.
What drawings do I need?
Planning drawings for the application, then more detailed building regulations drawings and structural calculations for building control. We prepare both.
Is a double-storey extension cheaper per square metre?
Usually yes. You pay for one set of foundations and one roof but get two floors of space, so the cost per square metre is often lower than a single-storey extension.