Part single, part two-storey extensions in Portstewart

Useful details for planning a part single, part two-storey extension in Portstewart.

Postcode districts: BT55
County / area: County Londonderry, 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: Portrush (2.7 miles), Coleraine (3.8 miles), Ballymoney (11.1 miles)
Distance to Derry: about 26.8 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 Portstewart we also work in Portrush, Coleraine and Ballymoney, and across the rest of County Londonderry. Postcode district in and near Portstewart: BT55.

What it costs in Portstewart

In Northern Ireland, which includes Portstewart, we'd expect a part single, part two-storey extension to cost around £63,500–£87,000 for a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total), or £1,760–£2,420 per m² including VAT. Professional fees for drawings and the structural engineer are listed separately on our prices page.

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 Portstewart

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 Portstewart homes

Structure at the step

The first-floor wall above often sits over the new open-plan space, so it needs a steel beam or frame to carry it. Loads come down at different points than in a full two-storey design, and the engineer sizes the foundations to suit each part.

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.

How we'd run your project

Understand the brief
At your home in Portstewart we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Get it approved
Once you're happy with the design we submit it to the council for Portstewart and deal with any questions from the planning officer.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

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

Do I need planning permission for a part single, part two-storey extension in Portstewart?

Portstewart is in Northern Ireland. 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.

Which postcodes do you cover around Portstewart?

We cover Portstewart (BT55) and nearby places including Portrush, Coleraine and Ballymoney, plus the rest of County Londonderry. The first site visit is free.

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

We also cover places near Portstewart, including:

Other extensions in Portstewart

All two-storey extension services in Portstewart · Part single, part two-storey extensions across County Londonderry

Ready to talk it through? Call us or send the form and we'll arrange a visit to your home in Portstewart.