Do You Need Planning Permission for an Extension in Jersey?

Short answer: in Jersey, almost certainly yes.

House extensions are the single most common reason islanders come to us, and they are also where the gap between UK expectations and Jersey reality is widest. The permitted development rights that let homeowners in England add a rear extension without an application are much narrower here. Assume you need permission, and treat it as good news if you turn out not to.

What the planners are actually assessing

An extension application is not judged on whether the drawing is attractive. It is judged against policy tests, and knowing which ones are coming is most of the work.

Scale and dominance. Does the extension read as subordinate to the original house, or does it overwhelm it? This is the test most homeowner-designed schemes fail, because the brief was “as much space as possible”.

Overlooking and privacy. Where do the new windows look? A first-floor window facing a neighbour’s garden or window is the most reliable way to attract both an objection and a refusal.

Daylight and overshadowing. What does the extension do to the neighbour’s light, particularly on tight urban plots in St Helier?

Character and materials. Does it sit properly with the existing building and the street? In a conservation area this test gets much sharper.

Site-specific constraints. Flood zone, listing, proximity to a boundary, drainage, trees, the green zone.

The constraints that decide your maximum size

Before anyone draws anything, these determine what is achievable:

• Whether the property or any structure on it is listed
• Whether you are in a conservation area
• The zoning of the site under the Island Plan — the built-up area behaves very differently from the green zone
• The boundary relationships — distances to neighbouring windows and gardens
• Whether a previous permission removed permitted development rights
• Flood risk designation

We check all of these at the free consultation, before you spend money on a design that the site will not carry.

Types of extension, and what each tends to raise

Single-storey rear — the most common, and usually the most straightforward. Main issues are depth relative to the neighbour and impact on their light. See single-storey extensions.

Two-storey — raises overlooking and dominance in a way a single storey does not. Nearly always needs careful window positioning. See double-storey extensions.

Side — often constrained by the gap to the boundary and by whether infilling the gap closes an important view or rhythm in the street. Party wall issues are common. See side extensions.

Wraparound — combines the issues of rear and side, and is more likely to trip the dominance test. See wraparound extensions.

Kitchen extension — usually a single-storey rear in planning terms, but with drainage and ventilation implications that matter at bye-law stage. See kitchen extensions.

The States also publish a decision tool for extensions and conservatories.

Planning permission is not enough to build

This is the part that surprises people most. Planning permission establishes that the development is acceptable in principle. It does not say your extension is buildable.

For that you need building bye-law approval under the Building Bye-Laws (Jersey) 2007 — a separate application, assessed against technical standards for structure, fire, insulation, drainage and ventilation. Your extension will also need structural design: beams over new openings, foundations, lintels.

Most planning agents produce planning drawings, get you permission, and then produce a minimal bye-law set. Your builder cannot price from either, so you pay for a third set of construction drawings.

We produce construction-standard drawings from the outset, and the structural engineering is in-house rather than subcontracted. See bye-law drawings for extensions.

What it costs to build

We do not quote build costs — that is your builder’s job — but for budgeting, get quotes from at least three Jersey builders, and get them against a drawing set detailed enough that all three are pricing the same thing. Pricing from a vague planning drawing produces three numbers that cannot be compared.

Start with the site, not the drawing

Book a free consultation. We visit, measure, check the constraints, and tell you what is realistically achievable before you commit. If the scheme you have in mind will not get permission, you will hear that from us first rather than from a case officer three months later.