Part single, part two-storey extensions in Rickmansworth

What we'd confirm first for a project in Rickmansworth.

Postcode districts: WD3
County / area: Hertfordshire, 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: Batchworth (0.7 miles), Croxley Green (1.2 miles), Chorleywood (1.9 miles)
Distance to Watford: about 3.7 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 district WD3 in and around Rickmansworth, along with neighbouring Batchworth, Croxley Green and Chorleywood.

What it costs in Rickmansworth

In the East of England, which includes Rickmansworth, we'd expect a part single, part two-storey extension to cost 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), or £2,060–£2,830 per m² including VAT. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

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 Rickmansworth

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 Rickmansworth homes

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.

The roof junction

Where the single-storey roof meets the two-storey wall you need a sound weathering detail, usually a lead or similar flashing, and enough height for roof lights or a lantern. We set the roof falls and the upstairs window sill heights together so they do not clash.

How we'd run your project

Understand the brief
At your home in Rickmansworth we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
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.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

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

How long does a part single, part two-storey 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 Rickmansworth?

We cover Rickmansworth (WD3) and nearby places including Batchworth, Croxley Green and Chorleywood, plus the rest of Hertfordshire. The first site visit is free.

How much does a part single, part two-storey extension cost in Rickmansworth?

Our guide for the East of England, which covers Rickmansworth, is £2,060–£2,830 per m² including VAT. A typical project with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total) comes to about £74,000–£102,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

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.

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.

Nearby

Other towns near Rickmansworth:

Other extensions in Rickmansworth

All two-storey extension services in Rickmansworth · Part single, part two-storey extensions across Hertfordshire

The quickest next step is a visit. We'll look at your house in Rickmansworth and give you an honest view of the options.