Do I Need Planning Permission for an Extension in Essex?

Most single-storey rear extensions in Essex do not need planning permission. They fall under Permitted Development (PD). But the rules are tighter than people think, and getting it wrong means an enforcement notice and tearing it down at your own cost. Here is the plain-English version.

What you can do under Permitted Development

Single-storey rear extension

• Detached house: up to 8m deep, max 4m high (3m at the eaves within 2m of boundary).
• Semi or terraced: up to 6m deep, same height limits.
• Must be at the rear, not in front of the principal elevation.
• Materials must be similar to the existing house.
• Total extensions and outbuildings can not cover more than 50% of the original garden.

For anything between 3m and 8m (detached) or 3m and 6m (other), you will need to apply for Prior Approval under the Larger Home Extension scheme. Your council notifies neighbours, who have 21 days to object.

Double-storey rear extension

• Max 3m deep under PD.
• Must be at least 7m from the rear boundary.
• Roof pitch must match the existing house.
• Windows on side elevations must be obscure-glazed and non-opening below 1.7m.

Side return or wrap-around

• PD allowed only if it does not extend forward of the principal elevation.
• Width capped at half the original house width.
• Wrap-arounds (rear plus side) usually need full planning. The combination breaks PD rules.

Loft conversion

• Up to 40m³ for terraced, 50m³ for semi or detached added volume.
• No extension above the existing roof line at the front.
• Dormers must be at least 20cm from the eaves.
• Hip-to-gable conversions are PD. Mansards usually are not.

When you definitely need full planning permission

• You live in a conservation area (lots of central Chelmsford, Brentwood, parts of Epping Forest, Maldon).
• The property is listed. Also needs Listed Building Consent.
• Permitted Development rights have been removed by an Article 4 direction (check your title deeds and council planning portal).
• The extension goes forward of the principal elevation (front extensions almost always need it).
• You are in a flat or maisonette. PD does not apply.

Building Control, separate, and always required

Whether you need planning or not, every extension needs Building Control approval. That covers structure, insulation, drainage, fire escape, ventilation. Two routes:

1. Full Plans application. Drawings approved before you start (safer for big jobs).
2. Building Notice. Start within 48 hours notice, inspector visits at key stages.

Budget £600 to £1,500 for Building Control fees on a typical extension.

What it actually costs in Essex (2026)

Extension type	Build cost (labour + materials)
Single-storey rear, 4×4m	£42,000 to £62,000
Single-storey rear, 6×4m	£58,000 to £85,000
Wrap-around or side return	£65,000 to £110,000
Double-storey rear	£75,000 to £130,000
Loft conversion (dormer)	£42,000 to £75,000

That is excluding kitchen, bathroom and finishes. Usually add 15 to 25%.

How we handle planning so you do not have to

• Free site visit and measure-up.
• Architect drawings sorted (we work with two local Essex practices).
• Planning application or Lawful Development Certificate submitted on your behalf.
• Building Control liaison through to sign-off.
• Structural engineer drawings for steels and foundations.

One team. One contact. From "we are thinking about it" to "the keys are yours."

Book a free extension consultation