Two-storey extensions for detached houses in Portslade

Quick reference for homeowners in Portslade.

Postcode districts: BN41
County / area: East Sussex, England
Price region: South East England
Guide price: £94,500–£127,000 (£2,260–£3,030 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: Hove (2.3 miles), Shoreham-by-Sea (2.6 miles), Brighton (3.5 miles)
Distance to Brighton: about 3.5 miles
First visit: Free, no obligation

About a two-storey extension for a detached house

A two-storey extension for a detached house is a two-floor addition to the side, rear or both of a house that stands on its own plot. Detached houses often have room on more than one side, so there is more choice of layout and fewer shared-wall issues. The design still needs to respect boundaries, neighbours' windows and the look of the house.

Around Portslade we also work in Hove, Shoreham-by-Sea and Brighton, and across the rest of East Sussex. Postcode district in and near Portslade: BN41.

What it costs in Portslade

Guide prices for two-storey extensions for detached houses in South East England are around £2,260–£3,030 per m² of new floor space, including VAT. For a typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space), that's roughly £94,500–£127,000. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
Essential	£2,070–£2,780 per m²	£87,000–£117,000
Standard	£2,260–£3,030 per m²	£94,500–£127,000
Premium	£2,710–£3,630 per m²	£113,500–£152,500

Planning and building regulations in Portslade

In England, a two-storey rear extension on a detached house can be permitted development within 3 m of the original rear wall and at least 7 m from the rear boundary, with matching roof pitch and materials, outside protected areas. Any two-storey side or wraparound extension needs planning permission, costing £548 (or £575 for applications made from 8 December 2026), with a decision due within 8 weeks of validation.

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 Portslade homes

Keeping it subordinate

Large detached houses can take a large extension, but councils still expect it to look secondary to the main house. A lower ridge, a modest set-back at the front and matching materials keep the proportions right, even on a wide plot.

Larger spans and steelwork

Bigger extensions often mean wider openings and longer spans, which need more steel and sometimes a steel frame. The engineer designs these early, because the size of the steel affects ceiling heights, floor depths and the cost.

How we'd run your project

Look at the house
We start in Portslade with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about two-storey extensions for detached houses in Portslade

How long does a two-storey extension for a detached house 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 Portslade?

We cover Portslade (BN41) and nearby places including Hove, Shoreham-by-Sea and Brighton, plus the rest of East Sussex. The first site visit is free.

How much does a two-storey extension for a detached house cost in Portslade?

Our guide for South East England, which covers Portslade, is £2,260–£3,030 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £94,500–£127,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Can I extend a detached house on both sides?

Sometimes. With planning permission, a council may accept extensions on both sides if the house stays well proportioned and keeps gaps to the boundaries. It is more common to extend on one side and the rear, or with a wraparound. We look at the plot as a whole before suggesting more than one extension.

Is a detached house extension a better investment than moving?

It often costs less than the gap between your house and a larger one nearby, once property tax, legal fees and removal costs are counted, but that depends on your area. Extending also has limits: every street has a ceiling price. We give you build costs so you can compare them with local asking prices.

Nearby

Nearby towns we cover for two-storey extensions for detached houses:

Other extensions in Portslade

All two-storey extension services in Portslade · Two-storey extensions for detached houses across East Sussex

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