House Extensions in Galway: Planning Permission and Building Regulations Basics

Extending is often the most sensible way to get the kitchen, living space or extra bedroom a family actually needs, without taking on the cost and upheaval of moving. The building work is the part homeowners picture, but the questions that decide whether a project runs smoothly usually come earlier: does it need planning permission, and what will it have to comply with once it is built? Here is a plain-English overview for Galway homeowners.

Exempted development: the 40 square metre rule

Irish planning regulations allow certain domestic extensions to be built without planning permission. The best-known limit is 40 square metres of floor area to the rear of the house — but that figure comes with conditions attached, and it is the conditions that catch people out.

In broad terms, the exemption applies to extensions at the rear, not the front or side facing a public road. Where the house has already been extended, any previous extensions count towards the same total, so a house with a 20 square metre extension from a previous owner has far less headroom than the number suggests. First-floor extensions are much more tightly limited than ground floor, and a minimum area of private open space must remain at the back of the house. There are also rules on window positions overlooking neighbouring properties.

Apartments, duplexes and protected structures are treated differently again, and a house in an Architectural Conservation Area or with a condition attached to its original permission may have had exemptions removed.

When you will need permission

You will generally need to apply for planning permission if the extension goes over the exempt floor area once past work is counted, extends to the front, changes the use of the building, or involves a protected structure. Bigger projects, garden rooms used as habitable accommodation, and anything where you are unsure of the site history are all worth checking properly.

The useful thing to know is that you do not have to guess. Galway City Council and Galway County Council both take Section 5 declaration requests, where you describe the proposed works and the council issues a formal decision on whether they are exempted development. It costs a fraction of a planning application and gives you something in writing. If there is any doubt at all — especially on a house that has been extended before — that written answer is far cheaper than discovering the problem when you go to sell.

Building regulations apply either way

This is the point most often missed: planning permission and building regulations are two separate systems. An extension that needs no planning permission still has to be built in compliance with the Building Regulations. They cover structure, fire safety, ventilation, drainage, sound, conservation of fuel and energy, and access.

In practice that shapes real decisions on site — foundation and structural design, how the new roof and walls are insulated and detailed, where drains run and how they connect, ventilation and smoke alarms, and the glazing and U-values in the new windows and doors. Extensions also come with paperwork under the building control regulations, including a commencement notice to the local authority before work starts, with heavier certification requirements above the 40 square metre threshold.

Where the windows and doors come in

On most extensions the rear wall is largely glass, so the glazing specification carries a lot of the comfort and energy performance of the finished room. Frame material, glazing spec and the door style all matter: a large sliding or bi-fold system needs the right structural opening designed in from the start, not fitted around afterwards. Our guide to patio doors and sliding systems covers the options in more detail, and the uPVC vs aluminium vs aluclad comparison explains where each frame material earns its place.

A sensible order of work

Start with what you want the space to do, then check the site history — original permission, any previous extensions, boundary distances and remaining garden area. Get clarity on exemption before designs are finalised, either through a professional or a Section 5 declaration. Then move to design and specification, and only then to build.

Doing it in that order means the design is shaped by what is actually allowed on your site, rather than being reworked after the fact.

KRB Construction & Windows Ltd builds extensions and supplies and fits windows and doors across Galway City and County Galway, along with the surrounding counties. If you are weighing up an extension, get in touch or request a quote with a few details about the house and what you have in mind. This article is general guidance — always confirm the planning position for your own property with your local authority or a planning professional.