Part single, part two-storey extensions in Hemel Hempstead
Adding a part single, part two-storey extension in Hemel Hempstead gives you two new rooms stacked on one footprint. Here's how we'd approach it, what it typically costs and the rules that apply in England.
What we'd confirm first for a project in Hemel Hempstead.
- Postcode districts
- HP1, HP2 and HP3
- 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
- Leverstock Green (0.8 miles), Abbots Langley (3.6 miles), Berkhamsted (5 miles)
- Distance to Watford
- about 7.2 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 Hemel Hempstead (HP1, HP2 and HP3) and the places around it, including Leverstock Green (0.8 miles), Abbots Langley (3.6 miles) and Berkhamsted.
What it costs in Hemel Hempstead
For budgeting in Hemel Hempstead, 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. 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 Hemel Hempstead
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 Hemel Hempstead homes
Where to put the two-storey part
The two-storey section usually works best away from the closest neighbour, with the single-storey part on that boundary side. We test a few positions against neighbours' windows, the upstairs layout and the roof shape before choosing the one to take forward.
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
Look at the house
We start in Hemel Hempstead with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Get it approved
Once you're happy with the design we submit it to the council for Hemel Hempstead and deal with any questions from the planning officer.
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 and sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.
Questions about part single, part two-storey extensions in Hemel Hempstead
Which postcodes do you cover around Hemel Hempstead?
We cover Hemel Hempstead (HP1, HP2 and HP3) and nearby places including Leverstock Green, Abbots Langley and Berkhamsted, plus the rest of Hertfordshire. The first site visit is free.
Do I need planning permission for a part single, part two-storey extension in Hemel Hempstead?
Hemel Hempstead 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.
How much does a part single, part two-storey extension cost in Hemel Hempstead?
Our guide for the East of England, which covers Hemel Hempstead, 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.
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.
Nearby
We also cover places near Hemel Hempstead, including:
Other extensions in Hemel Hempstead
- Rear
- Side
- Wraparound
- Over a garage
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Hemel Hempstead · 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.