First-floor extensions in Steyning

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

Postcode districts: BN5, BN44 and RH20
County / area: West Sussex, England
Price region: South East England
Guide price: £27,500–£40,000 (£1,980–£2,860 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: Lancing (4.1 miles), Shoreham-by-Sea (4.4 miles), Worthing (5.2 miles)
Distance to Crawley: about 16.8 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.

Around Steyning we also work in Lancing, Shoreham-by-Sea and Worthing, and across the rest of West Sussex. Postcode districts in and near Steyning: BN5, BN44 and RH20.

What it costs in Steyning

Most of the cost of a first-floor extension is set by its size and specification. For Steyning and the rest of South East England, our guide is £1,980–£2,860 per m² including VAT, so about £27,500–£40,000 for 4 m × 3.5 m of new first-floor space (14 m²). Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,820–£2,630 per m²	£25,500–£37,000
Standard	£1,980–£2,860 per m²	£27,500–£40,000
Premium	£2,380–£3,430 per m²	£33,500–£48,000

Planning and building regulations in Steyning

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 Steyning 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.

Matching the roofline

A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.

How we'd run your project

Measure and listen
A visit to Steyning to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
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.
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 Steyning

Which postcodes do you cover around Steyning?

We cover Steyning (BN5, BN44 and RH20) and nearby places including Lancing, Shoreham-by-Sea and Worthing, plus the rest of West Sussex. The first site visit is free.

How much does a first-floor extension cost in Steyning?

Our guide for South East England, which covers Steyning, is £1,980–£2,860 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £27,500–£40,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

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.

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

Nearby towns we cover for first-floor extensions:

Other extensions in Steyning

All two-storey extension services in Steyning · First-floor extensions across West Sussex

Ready to talk it through? Call us or send the form and we'll arrange a visit to your home in Steyning.