Planning Permission in Ireland — What You Can and Can't Build Without It

So folks, let me give you the short version first.

Most homeowners in Ireland assume that planning permission is the biggest hurdle between them and their project. Get the permission, and the rest follows.

It does not quite work like that.

Planning permission tells you that you are allowed to build something. It does not tell you what it will cost. It does not guarantee your engineer will be happy with the structure. It does not mean your builder is lined up, your spec is written, or your budget is real.

Permission is step one. And it is an important step. But it is only one step. And I have sat across the table from too many families in Dublin and across Ireland who got their permission, fell in love with what they were going to build, and then discovered that the build was €60,000 or €70,000 beyond what they could actually afford.

So. Let me walk you through what you can and cannot build without permission in Ireland, and then — just as importantly — what you need to do alongside the planning process to make sure the project is actually buildable when the permission arrives.

What you can build without planning permission in Ireland

The good news is that a significant amount of residential construction in Ireland is exempt from planning permission. The rules are set out in the Planning and Development Regulations, and they cover a wide range of common projects.

Extensions to the rear of a house. A single-storey extension to the rear of a house can be built without permission up to 40 square metres, provided the total floor area of the house plus the extension does not exceed the original floor area of the house plus 40 square metres. There are height restrictions — generally no higher than the eaves of the existing house — and it must not reduce the private open space to the rear of the house below 25 square metres.

Garden structures. Sheds, garden rooms, and similar structures can generally be built without permission provided they are within certain size limits and set back from the boundary. The rules vary depending on the structure and its use.

Walls and fences. In most cases, walls and fences up to 1.2 metres on a road boundary and 2 metres elsewhere can be erected without permission.

Internal works. Most internal alterations — removing walls, changing layouts, renovating kitchens and bathrooms — do not require planning permission, though they may require other approvals such as Building Regulations compliance or a Disability Access Certificate depending on the nature of the work.

Now. There are exceptions to all of the above. Houses in protected structures, houses in Architectural Conservation Areas, and houses where previous exemptions have already been used up all have different rules. If you are in any doubt at all, check with your local authority or your architect before you start anything.

What does require planning permission

As a general rule, you will need planning permission for:

Extensions that exceed the exempt thresholds — anything over 40 square metres to the rear, or any extension to the front of the house.

Changes of use — converting a house to apartments, converting a commercial building to residential, or any change that materially alters how a building is used.

New buildings — any new dwelling, outbuilding, or structure that does not fall within the exemptions.

Works to protected structures — almost any works to a protected structure require permission, including works that would be exempt on an ordinary house.

Significant alterations to the external appearance of a house — this includes replacing windows with a different style, changing the roof material, or adding dormer windows.

The bit most people miss — permission and cost are two different conversations

Here is the thing I want you to take away from this piece, because it is the thing I see go wrong most often.

Planning permission and construction cost are two separate conversations. And most homeowners treat them as one.

They get the architect. The architect draws up plans. The plans go for planning. And everyone waits — sometimes six months, sometimes longer — for the decision to come back before anyone has a serious conversation about what the build will actually cost.

Then the permission arrives. The family is excited. The project is real. And the cost plan — if anyone does one at all — comes back with a number that is significantly beyond what they had in their heads.

I'll be honest with you. That is a very hard conversation to have. The drawings are done. The permission is in. The family has been imagining this project for the better part of a year. And now they are being told the number does not work.

It does not have to happen that way.

Do the permission and the cost plan in parallel. While the architect is preparing the planning drawings, I can prepare a cost plan based on the proposed scheme. It will not be a final number — the drawings are not detailed enough for that yet — but it will tell you whether the project is in the right territory before you commit to a full set of construction drawings, before you go to tender, and before you fall in love with something you cannot afford to build.

That is the conversation worth having early. Not after.

When the planner says yes but the engineer says no

There is one more scenario I want to mention, because it catches people out more often than you would expect.

Planning permission is granted by the local planning authority. It is a land use decision. It tells you what you are allowed to build in principle.

It does not tell you whether the structure is engineerable. Whether the ground can support what you want to build. Whether the existing structure of your house can carry an additional storey. Whether the drainage on your site can accommodate the increased load.

Those are engineering questions. And the answers to them can materially affect both what you build and what it costs.

I have seen projects where planning permission was granted for exactly what the homeowner wanted — and the structural engineer then came back with a requirement for a significantly more expensive foundation solution because of the ground conditions on the site. The permission was valid. The cost was real. And nobody had flagged it until after the permission was in hand.

Get the engineer involved early. Alongside the architect, alongside the cost plan, alongside the planning application. Not after.

The five questions to ask before you start

Is my proposed project exempt from planning permission? Check the regulations, or ask your architect. Do not assume.

If permission is required, how long will it take? A standard planning application in Ireland takes approximately eight weeks for a decision, but objections, requests for further information, and appeals can extend this significantly.

What is the realistic cost of what I want to build? Commission a cost plan alongside the planning drawings, not after.

Are there any structural or engineering considerations I should know about early? Get the engineer to review the site and the scheme before too much money is spent on detailed drawings.

Do I need any other approvals alongside planning? Building Regulations compliance, Fire Safety Certificates, Disability Access Certificates — depending on your project, there may be additional approval requirements that affect your programme and your cost.

Anyway, that is the short version. The planning system in Ireland is more manageable than most people think — once you know the rules and you have the right people around you at the right time.

Permission is step one. Cost reality is step two. Do both in parallel — it saves months and money. → roryconnollyqs.ie/cost-plan

If I can help in any way, let me know.