Do I Need Planning Permission for an Extension in Northern Ireland?

This is the question that costs people the most money, because the wrong answer is only discovered after the foundations are in. It is also the question where English advice is most dangerous. Northern Ireland has its own planning legislation, its own permitted development order and its own decision makers, and several of the rules people quote confidently from English websites simply do not apply here.

Nothing on this page is legal advice. It is a filter: enough detail to tell you whether you are clearly fine, clearly not, or in the grey zone where you need to ring the council.

Who actually decides

Since 1 April 2015, planning in Northern Ireland has been run by the eleven district councils. Your application goes to Belfast City Council, or Lisburn and Castlereagh, or Ards and North Down, and so on — the council whose area the house sits in. The Department for Infrastructure keeps a role for regionally significant proposals, but a domestic extension is a local application and the council decides it.

That matters in practice. Each council has its own local development plan, its own planning officers and its own interpretation of the grey areas. Two neighbouring councils can take different views on the same detail. When you ring for advice, ring the council — not a national helpline, and not a builder who last did this three councils away.

Northern Ireland does have a shared online planning register where you can view and track applications, which is genuinely useful for seeing what has been approved on your street. But the register is not the decision maker. The council is.

Permitted development: the limits that catch most people

Permitted development is the set of works you can carry out without applying, set out in the Planning (General Permitted Development) Order (Northern Ireland) 2015. The Order has far more conditions than any article can list, but these are the ones that decide most household extensions.

How far you can go out the back

• Terraced or semi-detached house: up to 3 metres beyond the original rear wall.
• Detached house: up to 4 metres.

"Original" means the house as it was first built, not as you bought it. If a previous owner already took 2 metres off the allowance with a sunroom, you have what is left, not a fresh start.

Height

• Maximum 4 metres overall for the extension.
• If any part of the extension is within 2 metres of a boundary, the eaves must not exceed 3 metres.

That second rule is the one that quietly kills flat-roof designs on narrow Belfast plots.

Side extensions

A side extension must be single storey, no more than 4 metres high, and no wider than half the width of the original house. A two-storey side extension is not permitted development. Ever. Do not let anyone tell you otherwise.

The 50 per cent rule

Buildings and extensions must not cover more than half the curtilage — the land around the house, excluding the footprint of the original house itself. Garages, sheds and garden rooms all count. If your garden is already full of outbuildings, your extension allowance may be gone before you start.

The front of the house

Nothing forward of the principal elevation fronting a road. On a corner plot that can mean two elevations, which surprises people. Materials must also be similar in appearance to the existing house.

The English rule that does not exist here

In England there is a prior approval route — often called the larger home extension scheme — that lets householders build rear extensions of up to 6 or 8 metres by notifying the council rather than applying for permission.

Northern Ireland has no equivalent. If you want to go beyond the 3 or 4 metre limit here, you apply for planning permission in the ordinary way. Every year people arrive with an English article and a plan for a 6 metre rear extension, and it is always a full application. Budget the time and the fee for it.

What removes permitted development rights entirely

Conservation areas and areas of townscape character

Northern Ireland uses both designations. Conservation areas are the ones most people have heard of. Areas of Townscape Character, or ATCs, are a Northern Ireland designation covering places with a distinctive built character that falls short of conservation area status — Belfast has a number of them, and so do most of the larger towns.

Inside either, permitted development is cut back. Side extensions and cladding are commonly restricted, and demolition can need its own consent. The boundaries are not obvious from the street: a designation can run down the middle of a road so that one side is inside and the other is not. Check the map, do not assume.

Listed buildings

Northern Ireland grades listed buildings A, B+, B1 and B2, which is a different system from England's I, II* and II. Any work that affects the character of a listed building needs listed building consent from the council, and that includes things you would never expect — replacing windows, altering internal joinery, changing a roof covering. Listed building consent is separate from planning permission and you may need both.

Article 4 directions and planning conditions

A council can issue an Article 4 direction withdrawing permitted development rights across an area. Separately, many newer estates carry planning conditions on the original approval that restrict what you can do — a condition requiring a garage to be kept for parking is very common, and it applies whether or not the work would otherwise be permitted development. Read your deeds and the original approval before you assume.

Flats and maisonettes

Permitted development for extensions applies to houses. If you live in a flat, a maisonette or a converted property, you do not have these rights at all.

How to check properly, before you spend anything

1. Look at the planning register for your street. Approvals and refusals on similar houses tell you more about how your council thinks than any policy document.
2. Ring the council's planning office. Most will give informal guidance on a householder proposal. Some offer a paid pre-application discussion for anything more involved — worth it if the scheme is unusual.
3. Ask for a determination in writing if it is close. If you are relying on permitted development and the margin is small, get the council's view recorded. A verbal "that sounds fine" is worth nothing when you come to sell.
4. Check for a listing or a designation before you draw anything, not after.

What an application involves

A householder application needs drawings — existing and proposed plans and elevations, a site location plan and a block plan. Most people use an architectural technician or an architect; the drawings are also what your builder prices from, so they earn their fee twice.

Northern Ireland operates neighbour notification: the council writes to the occupiers of neighbouring properties telling them an application has been made and inviting comment. Objections do not automatically refuse an application, and they have to raise genuine planning matters — overlooking, loss of light, dominance — rather than the fact that a neighbour would rather you did not.

Processing times are published by each council and vary a good deal. The eight-week target quoted on English websites is not the Northern Ireland figure, and the real-world average in some councils is considerably longer. Look up your own council's published performance before you promise a builder a start date. Application fees are set by regulation and change periodically, so confirm the current householder fee with the council rather than trusting a number in an article.

Planning permission is not building control

These are two separate systems, run by two separate departments, often in the same council building, with two separate applications and two separate fees.

• Planning asks whether the building should exist: its size, siting, appearance and effect on neighbours.
• Building control asks whether it is safe and warm: structure, fire, insulation, ventilation, drainage, stairs.

You can need one, the other, both or neither. A permitted development extension still needs building control approval. A loft conversion that needs no planning permission at all still absolutely needs building control. There is a full explanation in our guide to building control in Northern Ireland.

What it costs once you have permission

Consent is the cheap part. If you want a realistic figure for the build itself, our guide to extension costs in Belfast has 2026 rates per square metre and a worked example, and the extension cost calculator will price your own dimensions from your postcode. If the planning position turns out to be difficult, a loft conversion or a garage conversion may get you the space with a far shorter route through the planning system.

Rules summarised here were reviewed in August 2026. Where they matter to your project, confirm them with your district council.