First-floor extensions in Southend-on-Sea

Before you start in Southend-on-Sea, here's what applies.

Postcode districts: SS0, SS1, SS2 and SS3
County / area: Essex, England
Price region: East of England
Guide price: £26,000–£37,500 (£1,850–£2,680 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: Rochford (3.1 miles), Hadleigh (4.6 miles), Rayleigh (5.8 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.

We cover Southend-on-Sea (SS0, SS1, SS2 and SS3) and the places around it, including Rochford (3.1 miles), Hadleigh (4.6 miles) and Rayleigh.

What it costs in Southend-on-Sea

Our guide for the East of England is £1,850–£2,680 per m² including VAT. On a project with 4 m × 3.5 m of new first-floor space (14 m²), that puts a first-floor extension in Southend-on-Sea at roughly £26,000–£37,500. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,710–£2,460 per m²	£24,000–£34,500
Standard	£1,850–£2,680 per m²	£26,000–£37,500
Premium	£2,220–£3,210 per m²	£31,000–£45,000

Planning and building regulations in Southend-on-Sea

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 Southend-on-Sea homes

Replacing the flat roof

The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.

Tying into the house

The new floor and walls must line up with the existing first floor, often through a new opening in the rear wall above the old one. Floor levels, the position of upstairs windows and the existing roof all affect where the opening can go, so we survey both floors carefully.

How we'd run your project

Visit and first ideas
One of our team visits your house in Southend-on-Sea, checks the walls, roof and drains, and sketches out options with you.
Get it approved
Once you're happy with the design we submit it to the council for Southend-on-Sea and deal with any questions from the planning officer.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
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 Southend-on-Sea

Which postcodes do you cover around Southend-on-Sea?

We cover Southend-on-Sea (SS0, SS1, SS2 and SS3) and nearby places including Rochford, Hadleigh and Rayleigh, plus the rest of Essex. The first site visit is free.

Who handles building regulations for a project in Southend-on-Sea?

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.

How much does a first-floor extension cost in Southend-on-Sea?

Our guide for the East of England, which covers Southend-on-Sea, is £1,850–£2,680 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £26,000–£37,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

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.

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.

Nearby

We also cover places near Southend-on-Sea, including:

Other extensions in Southend-on-Sea

All two-storey extension services in Southend-on-Sea · First-floor extensions across Essex

Book a free site visit in Southend-on-Sea and we'll tell you what's possible, what approvals you need and what the design stage would cost.