Double-storey extensions in Harborne

Double-storey extensions in Harborne: approvals and local details

Planning permission from Birmingham City Council is the first hurdle for most double-storey extensions in Harborne. Householder applications have an eight-week target for a decision, and Building Regulations approval and the Party Wall Act may also apply.

New first-floor bedrooms normally need an escape window with at least 0.33 m² of clear openable area.
A side extension of more than one storey always needs a householder planning application.
Party wall notices take one or two months to run, so they're best served as soon as planning is granted.

Postcode district: B17
Planning and building control: Birmingham City Council
From our West Bromwich base: 4 miles

Choices to weigh up in Harborne

Mixed-height extension

A two-storey section at the side with a single-storey section running across the back. This keeps the first floor away from neighbours' windows while still giving a wide kitchen-diner below. It's a practical compromise where planners have concerns about a full-depth two-storey rear extension, and it often simplifies the roof.

Combined side and rear

An L-shaped two-storey build wrapping the side and back of the house gives the biggest gain, sometimes two extra bedrooms. It's a substantial project with more steel and a complex roof junction, and it will need a householder planning application. Expect a longer programme and a careful plan for keeping the house secure while the roofs are joined.

What does your two-storey extension cost in Harborne?

Guide prices start at £52,000 and run to £135,000 depending on size and specification. A two-storey side extension on a three-bed semi, about 32 m² over two floors: around £68,000–£88,000.

Guide prices for double-storey extensions
Option	Guide price	Good to know
Compact two-storey rear (20–28 m² total)	£52,000 – £72,000	Bigger kitchen below, bedroom or bathroom above
Two-storey side or rear (30–40 m² total)	£68,000 – £98,000	The usual size on a three-bed semi
Large or combined side and rear (45 m²+)	£95,000 – £135,000	More steel, a complex roof and a longer programme

Guide ranges include VAT where it applies. A free survey turns this guide into a fixed, itemised price.

Before you book in Harborne

How long does a double-storey extension take?

Plan on 14–22 weeks on site, depending on size and roof complexity. Before that, allow time for drawings, a planning decision (councils aim to decide householder applications within 8 weeks), Building Regulations drawings and party wall notices. It's worth starting the design well ahead of when you need the space, because the approvals stage can take as long as the build.

How do I book a survey in Harborne?

Send the form on this page, use the guide-price tool or call 0800 088 6248 free. We'll ask a few questions about your two-storey extension and arrange a time to visit.

Is a double-storey extension better value than a single-storey one?

Per square metre, usually yes. Foundations and roofs are the expensive parts of any extension, and on a two-storey build they serve twice the floor area. You'll pay more in total and planning is less certain, but if you need a bedroom as well as downstairs space, building both together normally costs less than two separate projects years apart.

Who approves double-storey extensions in Harborne?

Usually both. Most two-storey extensions need a planning application to Birmingham City Council, and the structural work needs Building Regulations approval from its building control team or a registered building control approver.

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Other home improvements in Harborne

Want a guide figure first? Use our quote tool for your Harborne extension, then book a survey for a fixed price for the agreed specification.