First-floor extensions in Stockton-on-Tees

Before you start in Stockton-on-Tees, here's what applies.

Postcode districts: TS18, TS19 and TS21
County / area: County Durham, England
Price region: North East England
Guide price: £22,500–£33,000 (£1,620–£2,340 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Billingham (1.8 miles), Thornaby-on-Tees (2.5 miles), Middlesbrough (3.4 miles)
Distance to Darlington: about 9.8 miles
First visit: Free, no obligation

About a first-floor extension

A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.

Stockton-on-Tees sits about 9.8 miles from Darlington. Closer to home, Billingham is 1.8 miles away and Thornaby-on-Tees 2.5 miles.

What it costs in Stockton-on-Tees

For budgeting in Stockton-on-Tees, allow around £22,500–£33,000 for a first-floor extension with 4 m × 3.5 m of new first-floor space (14 m²). That's based on £1,620–£2,340 per m² including VAT for North East England. These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,490–£2,150 per m²	£21,000–£30,000
Standard	£1,620–£2,340 per m²	£22,500–£33,000
Premium	£1,940–£2,810 per m²	£27,000–£39,500

Planning and building regulations in Stockton-on-Tees

In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026).

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 Stockton-on-Tees homes

Escape and fire safety

A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs.

Can the existing structure take it?

Many single-storey extensions were built with foundations, walls and lintels sized for one storey. We find out what is there with trial holes and, where available, the original building control drawings. The engineer then decides whether to reuse, strengthen or rebuild parts of the structure.

How we'd run your project

Visit and first ideas
One of our team visits your house in Stockton-on-Tees, checks the walls, roof and drains, and sketches out options with you.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Questions about first-floor extensions in Stockton-on-Tees

Which postcodes do you cover around Stockton-on-Tees?

We cover Stockton-on-Tees (TS18, TS19 and TS21) and nearby places including Billingham, Thornaby-on-Tees and Middlesbrough, plus the rest of County Durham. The first site visit is free.

How long does a first-floor extension take?

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

Who handles building regulations for a project in Stockton-on-Tees?

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.

Will the first-floor extension match my house?

It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.

Can I build on top of my existing single-storey extension?

Often yes, but only after the structure has been checked. Foundations, walls and lintels built for one storey may not carry two. We dig trial holes, look for the original building control approval and ask the structural engineer to confirm what can stay, what needs strengthening and what must be rebuilt.

Nearby

We also cover places near Stockton-on-Tees, including:

Other extensions in Stockton-on-Tees

All two-storey extension services in Stockton-on-Tees · First-floor extensions across County Durham

The quickest next step is a visit. We'll look at your house in Stockton-on-Tees and give you an honest view of the options.