Part single, part two-storey extensions in North Watford

What we'd confirm first for a project in North Watford.

Postcode districts: WD24 and WD25
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: Watford (1.8 miles), West Watford (1.9 miles), Abbots Langley (2 miles)
Distance to Watford: about 1.8 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 WD24 and WD25 in and around North Watford, along with neighbouring Watford, West Watford and Abbots Langley.

What it costs in North Watford

For budgeting in North Watford, allow around £74,000–£102,000 for a part single, part two-storey extension with a 6 m × 4 m ground floor and a first floor over half of it (36 m² in total). That's based on £2,060–£2,830 per m² including VAT for the East of England. The fastest way to a firmer number is a free site visit, after which we price the design stage in writing.

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 North Watford

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 North Watford 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

Start at your house
We come to your home in North Watford, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering North Watford.
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 part single, part two-storey extensions in North Watford

Who handles building regulations for a project in North Watford?

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.

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

Our guide for the East of England, which covers North Watford, 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.

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

North Watford 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.

Which side should the two-storey part go on?

Usually the side furthest from the nearest neighbour's windows, so the single-storey part sits nearest them and keeps their light. Other factors are where the stairs land upstairs, which room needs the extra space and where drains run. We sketch options at the design stage and explain which is most likely to be approved.

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

We also cover places near North Watford, including:

Other extensions in North Watford

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

Want a figure first? Try our guide price tool, then book a free visit to firm it up.