Two-storey extensions for detached houses in Antrim

Before you start in Antrim, here's what applies.

Postcode districts: BT41
County / area: County Antrim, Northern Ireland
Price region: Northern Ireland
Guide price: £76,000–£101,500 (£1,800–£2,420 per m²)
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); most others need planning permission.
Nearest towns: Randalstown (4.2 miles), Crumlin (County Antrim) (6.7 miles), Ballyclare (8.8 miles)
Distance to Belfast: about 14.1 miles
First visit: Free, no obligation

About a two-storey extension for a detached house

A two-storey extension for a detached house is a two-floor addition to the side, rear or both of a house that stands on its own plot. Detached houses often have room on more than one side, so there is more choice of layout and fewer shared-wall issues. The design still needs to respect boundaries, neighbours' windows and the look of the house.

We cover Antrim (BT41) and the places around it, including Randalstown (4.2 miles), Crumlin (County Antrim) (6.7 miles) and Ballyclare.

What it costs in Antrim

Expect a two-storey extension for a detached house in Antrim to land somewhere around £76,000–£101,500 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Our Northern Ireland guide rate is £1,800–£2,420 per m², including VAT. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
Essential	£1,660–£2,230 per m²	£69,500–£93,500
Standard	£1,800–£2,420 per m²	£76,000–£101,500
Premium	£2,160–£2,900 per m²	£91,000–£122,000

Planning and building control in Antrim

In Northern Ireland, a two-storey rear extension on a detached house can be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary, with height, materials and roof pitch conditions. Side and wraparound designs normally need a planning application, which costs £347 per dwelling.

Approval in Northern Ireland: Planning application for works to a house: £347. Councils aim to decide local applications within an average of 15 weeks; many take longer.

Building control: Building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets.

Design points for Antrim homes

Choosing the best side

On a detached house you can often extend on either side or the rear. We look at orientation for daylight, where the stairs and landing are, the distance to each boundary, drains and trees, so the extension goes where it adds the most useful space.

Larger spans and steelwork

Bigger extensions often mean wider openings and longer spans, which need more steel and sometimes a steel frame. The engineer designs these early, because the size of the steel affects ceiling heights, floor depths and the cost.

How we'd run your project

Look at the house
We start in Antrim with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about two-storey extensions for detached houses in Antrim

How much does a two-storey extension for a detached house cost in Antrim?

Our guide for Northern Ireland, which covers Antrim, is £1,800–£2,420 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £76,000–£101,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Which postcodes do you cover around Antrim?

We cover Antrim (BT41) and nearby places including Randalstown, Crumlin (County Antrim) and Ballyclare, plus the rest of County Antrim. The first site visit is free.

Who handles building control for a project in Antrim?

We handle it as part of the project. What's needed in Northern Ireland: building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

Is a detached house extension a better investment than moving?

It often costs less than the gap between your house and a larger one nearby, once property tax, legal fees and removal costs are counted, but that depends on your area. Extending also has limits: every street has a ceiling price. We give you build costs so you can compare them with local asking prices.

Can I extend a detached house on both sides?

Sometimes. With planning permission, a council may accept extensions on both sides if the house stays well proportioned and keeps gaps to the boundaries. It is more common to extend on one side and the rear, or with a wraparound. We look at the plot as a whole before suggesting more than one extension.

Nearby

Nearby towns we cover for two-storey extensions for detached houses:

Other extensions in Antrim

All two-storey extension services in Antrim · Two-storey extensions for detached houses across County Antrim

Want a figure first? Try our guide price tool, then book a free visit to firm it up.