Two-storey extensions for semi-detached houses in Newcastle

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

Postcode districts: BT31 and BT33
County / area: County Down, Northern Ireland
Price region: Northern Ireland
Guide price: £49,500–£66,500 (£1,760–£2,380 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: Downpatrick (10.4 miles), Kilkeel (11.7 miles), Ballynahinch (12.7 miles)
Distance to Bangor (County Down): about 31.9 miles
First visit: Free, no obligation

About a two-storey extension for a semi-detached house

A two-storey extension for a semi-detached house is a two-floor addition to the rear, the open side, or both, designed around the attached neighbour on one side. The rear is often the simplest option and can sometimes be permitted development, while a side extension uses the gap on the detached side. Both need care with the shared party wall and the neighbour's light.

Around Newcastle we also work in Downpatrick, Kilkeel and Ballynahinch, and across the rest of County Down. Postcode districts in and near Newcastle: BT31 and BT33.

What it costs in Newcastle

Guide prices for two-storey extensions for semi-detached houses in Northern Ireland are around £1,760–£2,380 per m² of new floor space, including VAT. For a typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), that's roughly £49,500–£66,500. Design fees, structural calculations and approval fees are separate and listed on our prices page.

Spec	Per m²	A 4 m × 3.5 m footprint on two floors (28 m² of new floor space)
Essential	£1,620–£2,190 per m²	£45,500–£61,000
Standard	£1,760–£2,380 per m²	£49,500–£66,500
Premium	£2,110–£2,850 per m²	£59,000–£80,000

Planning and building control in Newcastle

In Northern Ireland, a two-storey rear extension on a semi 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. Upper side windows within 15 m of a boundary must be obscure and non-opening. A side extension normally needs planning, costing £347.

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 Newcastle homes

The attached neighbour's light

A two-storey rear extension next to the party wall can take light from the neighbour's rear windows. Councils often use a 45-degree test, so the first floor may need to be shorter than the ground floor or set in from the shared boundary.

Keeping the pair balanced

Semis are designed as matching pairs, and a side extension changes that balance. Setting the side extension back from the front wall and keeping its ridge lower helps the pair still read as a pair, which councils' design guides commonly ask for.

How we'd run your project

Look at the house
We start in Newcastle with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Drawings, then consent
We draw the scheme, check it against the rules in Northern Ireland, and take it through the right consent with the council.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
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 semi-detached houses in Newcastle

Do I need planning permission for a two-storey extension for a semi-detached house in Newcastle?

Newcastle is in Northern Ireland. 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.

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

Our guide for Northern Ireland, which covers Newcastle, is £1,760–£2,380 per m² including VAT. A typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space) comes to about £49,500–£66,500. 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 Newcastle?

We cover Newcastle (BT31 and BT33) and nearby places including Downpatrick, Kilkeel and Ballynahinch, plus the rest of County Down. The first site visit is free.

Will a side extension make my semi look like a terrace?

It can if it fills the whole gap to the boundary at first floor and the neighbour does the same. Many councils ask for a first-floor gap to the side boundary or a set-back for this reason. We design the extension to keep the semi reading as one of a pair.

What if my neighbour has already extended?

That often helps. An existing extension next door can reduce the effect of yours on their light, and may show what the council accepts on your street. It can also mean building alongside their wall, so we check its position, foundations and any windows facing your plot at the survey.

Nearby

We also cover places near Newcastle, including:

Other extensions in Newcastle

All two-storey extension services in Newcastle · Two-storey extensions for semi-detached houses across County Down

Tell us about your house in Newcastle and we'll call you back to arrange a free, no-obligation visit.