Two-storey extensions for semi-detached houses in Welshpool

Quick reference for homeowners in Welshpool.

Postcode districts: SY15, SY21 and SY22
County / area: Powys, Wales
Price region: Wales
Guide price: £51,500–£69,500 (£1,840–£2,480 per m²)
Approval route: Depends on position: rear (3 m first floor, 10.5 m to the boundary) and some side extensions (10.5 m, 1 m set-back) can be permitted development in Wales.
Nearest towns: Newtown (11.8 miles), Llanidloes (22 miles), Knighton (22.3 miles)
Distance to Newtown: about 11.8 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.

We cover postcode districts SY15, SY21 and SY22 in and around Welshpool, along with neighbouring Newtown, Llanidloes and Knighton.

What it costs in Welshpool

Expect a two-storey extension for a semi-detached house in Welshpool to land somewhere around £51,500–£69,500 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Our Wales guide rate is £1,840–£2,480 per m², including VAT. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	A 4 m × 3.5 m footprint on two floors (28 m² of new floor space)
Essential	£1,690–£2,290 per m²	£47,500–£64,000
Standard	£1,840–£2,480 per m²	£51,500–£69,500
Premium	£2,210–£2,980 per m²	£62,000–£83,500

Planning and building regulations in Welshpool

In Wales, a semi can take a two-storey rear extension under permitted development with the ground floor up to 4 m and the first floor up to 3 m beyond the original rear wall, 10.5 m from the rear boundary. A side extension can also be permitted development if it is 10.5 m from the side boundary, set back 1 m and adds no more than 50% width. Otherwise the fee is £585.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

Design points for Welshpool 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.

Rear, side or both

On a semi, a rear extension sits against the attached neighbour, while a side extension faces the detached neighbour and the street. We compare the space, cost and approval route for each, and for a wraparound, before you commit to one design.

How we'd run your project

Measure and listen
A visit to Welshpool 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 Wales, then apply for planning permission or a certificate of lawfulness, whichever fits.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Questions about two-storey extensions for semi-detached houses in Welshpool

Who handles building regulations for a project in Welshpool?

We handle it as part of the project. What's needed in Wales: building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency). We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

How long does a two-storey extension for a semi-detached house take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils normally decide householder applications within 8 weeks), 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.

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

Our guide for Wales, which covers Welshpool, is £1,840–£2,480 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 £51,500–£69,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

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.

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.

Nearby

Other towns near Welshpool:

Other extensions in Welshpool

All two-storey extension services in Welshpool · Two-storey extensions for semi-detached houses across Powys

Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.