House extensions in Ireland are becoming increasingly popular, but many homeowners remain uncertain about whether planning permission is needed. If you’re considering adding more space to your home, understanding the legal requirements is crucial. In this guide, we’ll walk you through the planning permission process for house extensions in Ireland, what exemptions exist, how to apply, and what pitfalls to avoid.
What Is Planning Permission in Ireland?
Planning permission is formal approval from your local authority allowing you to carry out construction, alterations, or extensions to your home. Its purpose is to ensure any development complies with zoning laws, environmental standards, and aesthetic guidelines.
There are two main types:
- Full planning permission – for detailed plans of proposed work.
- Outline planning permission – approval in principle, with details to follow.
Do I Always Need Planning Permission for a House Extension in Ireland?
Not always. Many small-scale house extensions in Ireland do not require planning permission, thanks to rules around “exempted development”. However, there are strict criteria you must meet.
House Extensions in Ireland: When Planning Permission Is Not Required
1. Rear Extensions up to 40 Square Metres
If your extension is at the back of the house and the combined floor area of all extensions since 1964 is under 40 square metres, planning permission is usually not required.
Conditions include:
- The extension must be at the rear of the house.
- The total floor space (new + existing extensions) must not exceed 40 m².
- It must not reduce private open space at the back of the property to less than 25 m².
2. Height Restrictions
- Max height for pitched roof: 4 metres
- Max height for flat roof: 3 metres
- Two-storey extensions must not be taller than the original house.
3. Distance from Boundaries
- Extensions above ground floor level must be at least 2 metres from any boundary.
- Windows on upper floors must avoid overlooking neighbours’ properties.
4. Conservatories, Garages, and Sheds
- Conservatories are treated like extensions.
- You can build a garage, shed, or greenhouse without permission if:
- It’s to the rear or side of the house.
- It’s under 25 m², and
- It doesn’t reduce open garden space below 25 m².
5. Front Porches
You can build a front porch without planning permission if:
- The area is under 2 m².
- It’s more than 2 metres from a public road.
- It complies with roof height rules.
When You Do Need Planning Permission for a House Extension in Ireland
1. Extending Beyond 40 Square Metres
If the total floor space of your extension(s) exceeds 40 m² (even cumulatively), you must apply for planning permission.
2. Side or Front Extensions
Extensions that project beyond the side or front building line usually require planning permission, regardless of size.
3. Two-Storey Extensions
Even if within the 40 m² limit, two-storey extensions are more strictly regulated and often need approval, especially due to potential impact on neighbouring properties.
4. Protected Structures and Conservation Areas
If your house is a listed or protected structure, or located in an architectural conservation area, you’ll almost certainly need planning permission—even for small changes.
5. Material Change of Use
If the use of a part of your home changes (e.g. converting a garage into a home office or business), planning permission may be needed depending on the nature and scale of the change.
Applying for Planning Permission for House Extensions in Ireland
Step 1: Pre-Planning Consultation
Before submitting an application, it’s wise to meet with a planning officer in your local authority. They’ll advise whether your proposal aligns with development plans.
Step 2: Submit Application
You’ll need:
- Completed planning application form
- Detailed drawings of the proposed extension
- Site layout plan
- Location map
- Newspaper notice and on-site notice
Step 3: Pay the Application Fee
As of 2025:
- House extension: €34
- Building a new house: €65
Step 4: Public Consultation Period
Neighbours and other interested parties can submit objections or observations within 5 weeks of the application being lodged.
Step 5: Decision Timeline
Most decisions are issued within 8 weeks, unless further information is requested.
Building Regulations and Compliance
Even if your extension is exempt from planning permission, you must still comply with Irish building regulations. These govern safety, ventilation, insulation, and structural standards.
You may also be required to submit a Commencement Notice to Building Control before starting work, depending on the size and scope of your project.
What Happens If You Build Without Planning Permission?
Carrying out development that needs planning permission without approval is a serious offence. You could face:
- Fines up to €5,000
- Legal enforcement
- Demolition orders
- Difficulties selling the property
You may apply for retention permission afterwards, but approval is not guaranteed and fines may still apply.
Key Takeaways: Planning Permission for House Extensions in Ireland
Scenario | Planning Permission Required? |
Rear extension under 40 m² | No |
Side or front extension | Yes |
Two-storey extension | Usually yes |
Extension exceeds 40 m² total | Yes |
Protected structures / listed homes | Yes |
Garage converted for business use | Yes |
Internal conservatory (rear) under 40m² | No |
Final Thoughts
Before starting any house extensions in Ireland, always ask: Do I need planning permission? If your project fits the exemption rules, you may proceed, but stay mindful of building regulations. For larger, more complex, or visible extensions, applying for planning permission is not just required—it’s the best way to future-proof your property.
For peace of mind, contact your local planning authority or consult a qualified architect or planning consultant. A well-informed approach can save you money, time, and legal hassle down the line.
If you’re looking for expert help with planning, designing, and building your home extension, OS Holding is here to guide you every step of the way. As one of Dublin’s most trusted building contractors, we specialise in stress-free home renovations and extensions—delivering on time, on budget, and to the highest standards. Get in touch with us today to start your dream home project with confidence.
