Two-storey extensions for semi-detached houses in County Tyrone

County Tyrone at a glance

Nation: Northern Ireland
Price region: Northern Ireland
Postcode areas: BT
Towns covered: 8 listed below, plus surrounding villages
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.
Site visits: Free, no obligation

What a two-storey extension for a semi-detached house involves

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.

Across County Tyrone we cover Omagh (BT78), Strabane (BT82), Dungannon (BT69), Cookstown (BT80), Coalisland (BT71) and Dromore (County Tyrone) (BT78), plus the smaller places around them.

Guide price in Northern Ireland

In Northern Ireland, which includes County Tyrone, we'd expect a two-storey extension for a semi-detached house to cost around £49,500–£66,500 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), or £1,760–£2,380 per m² including VAT. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	Typical project
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

Rules in Northern Ireland

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.

There is no Party Wall Act in Northern Ireland. Shared walls and boundaries are a matter of title and common law, so we agree access and record conditions with neighbours before work starts.

Getting the design right

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 work in County Tyrone

Free site visit
We visit your home in County Tyrone, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
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 and sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.

Towns we cover in County Tyrone

Two-storey extensions for semi-detached houses in County Tyrone: questions

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

In Northern Ireland our guide is £1,760–£2,380 per m² including VAT, so about £49,500–£66,500 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

Does a two-storey extension add value to a semi-detached house?

It usually adds value, but the gain is never certain. Nationwide's 2025 research found that 10% more floor area was linked to about 5% higher value, and that adding a double bedroom and bathroom to a three-bed, one-bathroom house could add up to 24%. Every street has a ceiling price, so check local sales first.

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.

Will I need planning permission in County Tyrone?

County Tyrone 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.

Neighbouring areas

All extension services in County Tyrone · About two-storey extensions for semi-detached houses