Two-storey extensions for semi-detached houses in Northallerton

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

Postcode districts: DL6 and DL7
County / area: North Yorkshire, England
Price region: Yorkshire and the Humber
Guide price: £51,500–£69,500 (£1,840–£2,480 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); a two-storey side extension needs planning permission.
Nearest towns: Thirsk (8.1 miles), Yarm (11.8 miles), Catterick Garrison (12 miles)
Distance to York: about 29.9 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.

We cover postcode districts DL6 and DL7 in and around Northallerton, along with neighbouring Thirsk, Yarm and Catterick Garrison.

What it costs in Northallerton

Guide prices for two-storey extensions for semi-detached houses in Yorkshire and the Humber are around £1,840–£2,480 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 £51,500–£69,500. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

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 Northallerton

In England, 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 matching materials and roof pitch. A two-storey side or wraparound extension always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026). Protected areas such as conservation areas exclude two-storey rear permitted development.

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

Design points for Northallerton homes

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.

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 Northallerton with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Get it approved
Once you're happy with the design we submit it to the council for Northallerton and deal with any questions from the planning officer.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
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 Northallerton

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

Northallerton is in England, so England planning rules apply. Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Who handles building regulations for a project in Northallerton?

We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

Which postcodes do you cover around Northallerton?

We cover Northallerton (DL6 and DL7) and nearby places including Thirsk, Yarm and Catterick Garrison, plus the rest of North Yorkshire. The first site visit is free.

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.

Should I extend my semi to the side or the rear?

It depends on your plot and what you need. A rear extension keeps the side drive and can sometimes be permitted development, but it affects the attached neighbour. A side extension keeps the rear garden but always needs planning permission in England. We compare both at the free site visit.

Nearby

Other towns near Northallerton:

Other extensions in Northallerton

All two-storey extension services in Northallerton · Two-storey extensions for semi-detached houses across North Yorkshire

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