What is a side extension?
A side extension builds into the space beside a semi-detached or detached house, often over a driveway or side passage. It can be single-storey, for a utility room, downstairs toilet or study, or two-storey to add a bedroom above.
How much does a side extension cost in Helensburgh?
In Helensburgh, a side extension typically costs £1,650–£2,550 per m² of floor area, including VAT at 20% (standard rate). For a typical 28 m² project that is roughly £46,000–£71,500. Prices in Scotland sit near the national average for this kind of work, and the range for Helensburgh reflects that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (20 m²) | £33,000–£51,000 |
| Typical project (28 m²) | £46,000–£71,500 |
| Larger project (39 m²) | £64,500–£99,500 |
| Rate per m² | £1,650–£2,550 |
The biggest cost drivers are:
- Boundary walls and access for materials
- Internal fit-out of the new rooms
- Roof design and tile matching
- Single or two storeys
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 side extension in Helensburgh?
Before anything is built in Helensburgh, we confirm which approvals apply in Scotland. In Scotland single-storey side extensions can be permitted development if they do not come forward of a side wall facing a road and stay within the height and boundary limits. Two-storey side extensions usually need planning permission, and a building warrant is needed before work starts.
Scotland has no Party Wall Act. Work on shared walls is governed by your title deeds, the Tenements (Scotland) Act 2004 for flats, and common law, so we agree arrangements with neighbours in writing before work starts.
We check this for your address before design work starts, so there are no surprises later.
What we handle
From survey to sign-off, the job normally involves:
- Planning drawings and application
- Foundations and drainage alterations
- Opening into the existing house
- Building control completion
- Walls, roof and windows to match the house
- Structural calculations
How long does it take?
The build itself usually takes 10 to 16 weeks on site depending on size and storeys. Design and approvals come first and typically take 3 to 4 months, depending on the approval route.
Building in Helensburgh
Scotland’s housing ranges from sandstone tenements and villas to post-war and modern estates, and the building warrant system shapes how projects are planned.
Our Helensburgh coverage includes postcode districts G84, and we also work in nearby places such as Greenock, Dumbarton and Dunoon.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about side extensions in Helensburgh
Will I lose my driveway?
A side extension often takes the side drive. We look at whether parking can be kept at the front and whether a dropped kerb is needed.
How long does a side extension take in Helensburgh?
Typically 10 to 16 weeks on site depending on size and storeys. Design and approvals beforehand usually take 3 to 4 months.
Will a two-storey side extension look odd?
Not if it is designed well. Setting it back from the front and keeping the roof lower than the main ridge usually gives a natural look and is what most councils ask for.
Can a side extension go over a drain?
Often yes, with a build-over agreement from the water company or by rerouting the drain. We check this during the survey.
Do I need planning permission for a side extension in Helensburgh?
In Scotland single-storey side extensions can be permitted development if they do not come forward of a side wall facing a road and stay within the height and boundary limits. Two-storey side extensions usually need planning permission, and a building warrant is needed before work starts.
How much does a side extension cost in Helensburgh?
In Helensburgh, a side extension typically costs £1,650–£2,550 per m² of floor area, including VAT at 20% (standard rate). A typical 28 m² project comes to roughly £46,000–£71,500. Your fixed price depends on the survey and drawings.