Part single, part two-storey extensions in Billericay

Quick reference for homeowners in Billericay.

Postcode districts: CM4, CM11 and CM12
County / area: Essex, England
Price region: East of England
Guide price: £74,000–£102,000 (£2,060–£2,830 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: Basildon (4.5 miles), Wickford (4.6 miles), Brentwood (4.9 miles)
Distance to Southend-on-Sea: about 14.1 miles
First visit: Free, no obligation

About a part single, part two-storey extension

A part single, part two-storey extension is an extension where the ground floor is wider or deeper than the floor above, so only part of it rises to two storeys. It usually gives a large kitchen or living area with roof lights below and one bedroom or bathroom above. It is often a good way to add space while limiting the effect on neighbours.

We cover postcode districts CM4, CM11 and CM12 in and around Billericay, along with neighbouring Basildon, Wickford and Brentwood.

What it costs in Billericay

Expect a part single, part two-storey extension in Billericay to land somewhere around £74,000–£102,000 for a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total). Our East of England guide rate is £2,060–£2,830 per m², including VAT. These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

Spec	Per m²	A 6 m × 4 m ground floor and a first floor over half of it (36 m² in total)
Essential	£1,900–£2,610 per m²	£68,000–£94,000
Standard	£2,060–£2,830 per m²	£74,000–£102,000
Premium	£2,470–£3,400 per m²	£89,000–£122,500

Planning and building regulations in Billericay

In England, the extension can only be permitted development if it goes no more than 3 m beyond the original rear wall and stays at least 7 m from the rear boundary, with matching materials and roof pitch. We check the whole design against the rules, including the 50% garden coverage limit. If any part fails, or extends beyond a side wall on two floors, you need 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 Billericay homes

Light into the kitchen

The single-storey part is the place for roof lights or a lantern, which bring daylight deep into the plan. In England, glazing is normally limited to 25% of the new floor area plus any windows removed, unless calculations show the house still performs, so we plan the balance early.

Structure at the step

The first-floor wall above often sits over the new open-plan space, so it needs a steel beam or frame to carry it. Loads come down at different points than in a full two-storey design, and the engineer sizes the foundations to suit each part.

How we'd run your project

Visit and first ideas
One of our team visits your house in Billericay, checks the walls, roof and drains, and sketches out options with you.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Questions about part single, part two-storey extensions in Billericay

Who handles building regulations for a project in Billericay?

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.

Which postcodes do you cover around Billericay?

We cover Billericay (CM4, CM11 and CM12) and nearby places including Basildon, Wickford and Brentwood, plus the rest of Essex. The first site visit is free.

Do I need planning permission for a part single, part two-storey extension in Billericay?

Billericay is in England, so England planning rules apply. 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. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Can the single-storey part be deeper than the two-storey part?

With planning permission, yes, and that is often the point of the design: the ground floor projects further into the garden while the first floor stays back from neighbours. Under permitted development, the depth limits for extensions of more than one storey can apply to the whole extension, so we confirm which route applies before drawings are finalised.

Can I add roof lights to the single-storey part?

Yes. Roof lights or a lantern over the single-storey part are one of the main reasons to choose this design, as they light the middle of a deep kitchen. In England they count towards the Part L glazing allowance, normally 25% of the new floor area plus windows removed, so we balance them with the rear doors.

Nearby

The same service in neighbouring towns:

Other extensions in Billericay

All two-storey extension services in Billericay · Part single, part two-storey extensions across Essex

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