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 Blackwood?
In Blackwood, a double-storey extension typically costs £1,500–£2,300 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £54,000–£83,000. Building costs in Wales run about 8% below the UK average, and the figures for Blackwood are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £37,500–£57,500 |
| Typical project (36 m²) | £54,000–£83,000 |
| Larger project (50 m²) | £75,000–£115,000 |
| Rate per m² | £1,500–£2,300 |
What moves the price most:
- Total floor area across both floors
- Scaffolding and access to the rear
- Brick matching and external finishes
- Roof design and how it joins the existing roof
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a double-storey extension in Blackwood?
Before anything is built in Blackwood, we confirm which approvals apply in Wales. In Wales a rear extension of more than one storey can be permitted development if the ground floor projects no more than 4 metres and the upper floor no more than 3 metres, with at least 10.5 metres to the rear boundary and obscure-glazed upper side windows. It is not permitted development in conservation areas, National Parks or National Landscapes, so many double-storey extensions need a householder application.
The Party Wall etc. Act 1996 applies in Wales, so notices must be served before work on a shared wall, on the boundary, or excavation close to a neighbour’s foundations.
We check this for your address before design work starts, so there are no surprises later.
What we handle
Handled as part of most double-storey extensions:
- Design drawings and planning application
- Electrics, heating, plumbing and plastering
- Windows, doors and staircase alterations
- Building control sign-off
- Opening up at both levels with steel beams
- Structural engineer’s calculations
How long does it take?
Expect 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 Blackwood
Wales has many terraced valley streets, stone cottages and post-war estates, so extension designs are shaped by slopes, materials and local character.
Blackwood sits in Mid Glamorgan, about 13 miles north of Cardiff. We cover the whole of Blackwood, including postcodes NP12.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 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
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about double-storey extensions in Blackwood
Do I need planning permission for a double-storey extension in Blackwood?
In Wales a rear extension of more than one storey can be permitted development if the ground floor projects no more than 4 metres and the upper floor no more than 3 metres, with at least 10.5 metres to the rear boundary and obscure-glazed upper side windows. It is not permitted development in conservation areas, National Parks or National Landscapes, so many double-storey extensions need a householder application.
How much does a double-storey extension cost in Blackwood?
In Blackwood, a double-storey extension typically costs £1,500–£2,300 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £54,000–£83,000. Your fixed price depends on the survey and drawings.
Who approves a double-storey extension in Blackwood?
Planning matters in Blackwood go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
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.
How close can it be to my neighbour?
Councils look at loss of light and outlook for neighbours. Many apply a 45-degree guideline from the nearest neighbouring window. We design to the council’s published guidance to give the application the best chance.
Will the first floor need a new staircase?
Not normally. The new rooms are reached from the existing landing, though a doorway or short corridor may need to be formed.