What is a side extension?
A side extension builds into the space beside a semi-detached or detached house, often over a driveway or side passage. It can be single-storey, for a utility room, downstairs toilet or study, or two-storey to add a bedroom above.
How much does a side extension cost in Hatfield?
In Hatfield, a side extension typically costs £1,800–£2,800 per m² of floor area, including VAT at 20% (standard rate). For a typical 28 m² project that is roughly £50,500–£78,500. Prices across the East of England are typically 6% above the UK average for this kind of work, which is reflected in the range for Hatfield. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (20 m²) | £36,000–£56,000 |
| Typical project (28 m²) | £50,500–£78,500 |
| Larger project (39 m²) | £70,000–£109,000 |
| Rate per m² | £1,800–£2,800 |
Your quote will depend mainly on:
- Boundary walls and access for materials
- Roof design and tile matching
- Internal fit-out of the new rooms
- Steel work where the side wall is opened
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a side extension in Hatfield?
Whether you need planning permission depends on your house and its location in England. In England a single-storey side extension can be permitted development if it is no more than 4 metres high and no wider than half the width of the original house. Side extensions of more than one storey always need planning permission, as do side extensions in conservation areas, National Parks and National Landscapes.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
On a typical side extension we handle:
- Planning drawings and application
- Building control completion
- Electrics, heating and plastering
- Walls, roof and windows to match the house
- Structural calculations
- Foundations and drainage alterations
How long does it take?
Allow 10 to 16 weeks on site depending on size and storeys. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Hatfield
Across the East of England, 1930s and post-war semis, newer estates and rural cottages all feature, each with different extension and loft options.
From AL10 outwards, we take on projects throughout Hatfield and the surrounding parts of Hertfordshire.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about side extensions in Hatfield
How long does a side extension take in Hatfield?
Typically 10 to 16 weeks on site depending on size and storeys. Design and approvals beforehand usually take 3 to 4 months.
How close to the boundary can I build?
You can build up to the boundary, but the eaves height near it is limited under permitted development, and planning officers often want a gap at first floor. If you build on or near a shared boundary, party wall rules may apply.
Can a side extension go over a drain?
Often yes, with a build-over agreement from the water company or by rerouting the drain. We check this during the survey.
How much does a side extension cost in Hatfield?
In Hatfield, a side extension typically costs £1,800–£2,800 per m² of floor area, including VAT at 20% (standard rate). A typical 28 m² project comes to roughly £50,500–£78,500. Your fixed price depends on the survey and drawings.
Can I build a side extension without planning permission?
In England a single-storey side extension can be permitted development if it is no more than 4 metres high and no wider than half the original house, and the house is not in a conservation area or similar protected land. Two-storey side extensions always need planning permission.