Two-storey extensions for detached houses in Hemel Hempstead

Before you start in Hemel Hempstead, here's what applies.

Postcode districts: HP1, HP2 and HP3
County / area: Hertfordshire, England
Price region: East of England
Guide price: £88,500–£119,000 (£2,110–£2,830 per m²)
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension 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 two-storey extension for a detached house

This service suits you if you own a detached house and want a substantial amount of extra space, whether a side extension over a drive, a rear extension into the garden or a wraparound. You get a survey of the whole plot, options that compare layouts and costs, the approvals your nation needs, structural design and the build, carried out by vetted teams working under S&K.

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 £88,500–£119,000 for a two-storey extension for a detached house with a 3 m × 7 m footprint on two floors (42 m² of new floor space). That's based on £2,110–£2,830 per m² including VAT for the East of England. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
Essential	£1,940–£2,610 per m²	£81,500–£109,500
Standard	£2,110–£2,830 per m²	£88,500–£119,000
Premium	£2,530–£3,400 per m²	£106,500–£143,000

Planning and building regulations in Hemel Hempstead

In England, a two-storey rear extension on a detached house can be permitted development within 3 m of the original rear wall and at least 7 m from the rear boundary, with matching roof pitch and materials, outside protected areas. Any two-storey side or wraparound extension needs planning permission, costing £548 (or £575 for applications made from 8 December 2026), with a decision due within 8 weeks of validation.

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

Choosing the best side

On a detached house you can often extend on either side or the rear. We look at orientation for daylight, where the stairs and landing are, the distance to each boundary, drains and trees, so the extension goes where it adds the most useful space.

Keeping it subordinate

Large detached houses can take a large extension, but councils still expect it to look secondary to the main house. A lower ridge, a modest set-back at the front and matching materials keep the proportions right, even on a wide plot.

How we'd run your project

Understand the brief
At your home in Hemel Hempstead we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Questions about two-storey extensions for detached houses in Hemel Hempstead

Do I need planning permission for a two-storey extension for a detached house in Hemel Hempstead?

Hemel Hempstead is in England, so England planning rules apply. Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

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.

How much does a two-storey extension for a detached house cost in Hemel Hempstead?

Our guide for the East of England, which covers Hemel Hempstead, is £2,110–£2,830 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £88,500–£119,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

How big an extension can a detached house take?

It depends on the plot, the boundaries and local design policy rather than a fixed limit. Under permitted development in England, extensions must not cover more than 50% of the land around the original house. With planning permission, the council judges size on proportion, neighbours and the character of the area.

Can I extend a detached house on both sides?

Sometimes. With planning permission, a council may accept extensions on both sides if the house stays well proportioned and keeps gaps to the boundaries. It is more common to extend on one side and the rear, or with a wraparound. We look at the plot as a whole before suggesting more than one extension.

Nearby

Close to Hemel Hempstead? We work across the area, including:

Other extensions in Hemel Hempstead

All two-storey extension services in Hemel Hempstead · Two-storey extensions for detached houses across Hertfordshire

Ready to talk it through? Call us or send the form and we'll arrange a visit to your home in Hemel Hempstead.