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 Johnstone?
In Johnstone, a double-storey extension typically costs £1,600–£2,400 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £57,500–£86,500. Building costs in Scotland are close to the UK average, so the figures for Johnstone are close to our national guide. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £40,000–£60,000 |
| Typical project (36 m²) | £57,500–£86,500 |
| Larger project (50 m²) | £80,000–£120,000 |
| Rate per m² | £1,600–£2,400 |
What moves the price most:
- Roof design and how it joins the existing roof
- Scaffolding and access to the rear
- Bathrooms or en-suites on the first floor
- Total floor area across both floors
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a double-storey extension in Johnstone?
Here is how the rules work for a double-storey extension in Scotland. In Scotland an extension of more than one storey is only permitted development if it is at least 10 metres from every boundary and no higher than the existing ridge, so most need planning permission. A building warrant is needed before work starts.
In Scotland a building warrant is needed before work starts on most extensions, loft conversions and conversions. It is issued by the council’s building standards service. When the work is finished, a completion certificate is submitted and accepted by the council after inspection.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
Handled as part of most double-storey extensions:
- Opening up at both levels with steel beams
- Brick or block walls, floors and a roof tied into the house
- Design drawings and planning application
- Windows, doors and staircase alterations
- Building control sign-off
- Foundations, drainage and scaffolding
How long does it take?
Build time is typically 14 to 20 weeks on site, after planning and building control approval. Design and approvals come first and typically take 3 to 4 months, depending on the approval route.
Building in Johnstone
In Scotland, bungalows and one-and-a-half-storey homes are common, so dormer conversions are a popular way to add bedrooms.
If your home is in Johnstone or close by in Paisley, Barrhead and Erskine, a free home visit is the first step.
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
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about double-storey extensions in Johnstone
Can I live at home during the work?
Most families stay put. The shell is built first and the house is opened up late in the job, so disruption inside is limited to a few weeks.
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.
Who approves a double-storey extension in Johnstone?
Planning matters in Johnstone go to the council covering your address, and the work needs a building warrant. We prepare and submit the applications for you.
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.
How much does a double-storey extension cost in Johnstone?
In Johnstone, a double-storey extension typically costs £1,600–£2,400 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £57,500–£86,500. Your fixed price depends on the survey and drawings.
Do I need planning permission for a double-storey extension in Johnstone?
In Scotland an extension of more than one storey is only permitted development if it is at least 10 metres from every boundary and no higher than the existing ridge, so most need planning permission. A building warrant is needed before work starts.