First-floor extensions in Gosport
Thinking about a first-floor extension in Gosport? We design it, take it through the approvals it needs and build it, with one team responsible from the first visit to the final certificate.
What we'd confirm first for a project in Gosport.
- Postcode districts
- PO12 and PO13
- County / area
- Hampshire, 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
- Portsmouth (1.7 miles), Southsea (1.9 miles), Fareham (4.5 miles)
- Distance to Southampton
- about 14.2 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 postcode districts PO12 and PO13 in and around Gosport, along with neighbouring Portsmouth, Southsea and Fareham.
What it costs in Gosport
For budgeting in Gosport, allow around £27,500–£40,000 for a first-floor extension with 4 m × 3.5 m of new first-floor space (14 m²). That's based on £1,980–£2,860 per m² including VAT for South East England. 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 Gosport
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 Gosport homes
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.
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.
How we'd run your project
Visit and first ideas
One of our team visits your house in Gosport, 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.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.
Questions about first-floor extensions in Gosport
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.
Which postcodes do you cover around Gosport?
We cover Gosport (PO12 and PO13) and nearby places including Portsmouth, Southsea and Fareham, plus the rest of Hampshire. The first site visit is free.
How much does a first-floor extension cost in Gosport?
Our guide for South East England, which covers Gosport, 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.
What happens to the room below while the first floor is built?
The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.
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
Other towns near Gosport:
Other extensions in Gosport
- Rear
- Side
- Wraparound
- Part two-storey
- Over a garage
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Gosport · First-floor extensions across Hampshire
Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.