Part single, part two-storey extensions in Larne

Larne: the key facts for this kind of project.

Postcode districts: BT40
County / area: County Antrim, Northern Ireland
Price region: Northern Ireland
Guide price: £63,500–£87,000 (£1,760–£2,420 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary.
Nearest towns: Carrickfergus (9.3 miles), Ballyclare (10 miles), Greenisland (10.6 miles)
Distance to Belfast: about 18 miles
First visit: Free, no obligation

About a part single, part two-storey extension

A part single, part two-storey extension is an extension where the ground floor is wider or deeper than the floor above, so only part of it rises to two storeys. It usually gives a large kitchen or living area with roof lights below and one bedroom or bathroom above. It is often a good way to add space while limiting the effect on neighbours.

Around Larne we also work in Carrickfergus, Ballyclare and Greenisland, and across the rest of County Antrim. Postcode district in and near Larne: BT40.

What it costs in Larne

Our guide for Northern Ireland is £1,760–£2,420 per m² including VAT. On a project with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total), that puts a part single, part two-storey extension in Larne at roughly £63,500–£87,000. These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

Spec	Per m²	A 6 m × 4 m ground floor and a first floor over half of it (36 m² in total)
Essential	£1,620–£2,230 per m²	£58,500–£80,000
Standard	£1,760–£2,420 per m²	£63,500–£87,000
Premium	£2,110–£2,900 per m²	£76,000–£104,500

Planning and building control in Larne

In Northern Ireland, the extension can be permitted development if it goes no more than 3 m beyond the original rear wall and stays at least 7 m from the rear boundary, with height, materials and roof pitch conditions met. Specified protected areas are excluded. If the design goes further, a planning application costs £347 per dwelling, and building control approval is needed either way.

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 Larne homes

Where to put the two-storey part

The two-storey section usually works best away from the closest neighbour, with the single-storey part on that boundary side. We test a few positions against neighbours' windows, the upstairs layout and the roof shape before choosing the one to take forward.

The roof junction

Where the single-storey roof meets the two-storey wall you need a sound weathering detail, usually a lead or similar flashing, and enough height for roof lights or a lantern. We set the roof falls and the upstairs window sill heights together so they do not clash.

How we'd run your project

Measure and listen
A visit to Larne to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Design and approvals
We draw the extension and check it against the rules for Northern Ireland, then apply for planning permission or a certificate of lawfulness, whichever fits.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.

Questions about part single, part two-storey extensions in Larne

Who handles building control for a project in Larne?

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.

How much does a part single, part two-storey extension cost in Larne?

Our guide for Northern Ireland, which covers Larne, is £1,760–£2,420 per m² including VAT. A typical project with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total) comes to about £63,500–£87,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

How long does a part single, part two-storey extension take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils aim to decide local applications within an average of 15 weeks; many take longer), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.

Can the single-storey part be deeper than the two-storey part?

With planning permission, yes, and that is often the point of the design: the ground floor projects further into the garden while the first floor stays back from neighbours. Under permitted development, the depth limits for extensions of more than one storey can apply to the whole extension, so we confirm which route applies before drawings are finalised.

Which side should the two-storey part go on?

Usually the side furthest from the nearest neighbour's windows, so the single-storey part sits nearest them and keeps their light. Other factors are where the stairs land upstairs, which room needs the extra space and where drains run. We sketch options at the design stage and explain which is most likely to be approved.

Nearby

Nearby towns we cover for part single, part two-storey extensions:

Other extensions in Larne

All two-storey extension services in Larne · Part single, part two-storey extensions across County Antrim

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