Home Extension Costs in Ireland: What to Budget (2026)

Building an extension is one of the biggest investments you can make in your home. Get the budget right from the start and you will avoid the stress that comes with unexpected costs halfway through the project.

This guide covers realistic per-square-metre costs for different extension types in Ireland, along with the additional expenses that often catch people out.

Extension Costs Per Square Metre

As a general rule, budget between 2,000 and 3,500 euro per square metre for a standard single-storey rear extension in Ireland. This assumes a basic to mid-range specification including foundation, walls, roof, windows, electrics, plumbing, plastering, and basic finishes.

A typical 20 square metre kitchen extension therefore costs between 40,000 and 70,000 euro. A larger 40 square metre open-plan extension runs from 80,000 to 140,000 euro.

Two-storey extensions cost more overall but less per square metre, typically 1,800 to 3,000 euro per square metre because the foundation and roof costs are shared across two floors.

High-spec finishes such as large-format glazing, underfloor heating, or premium kitchen fit-out can push costs to 3,500 to 5,000 euro per square metre.

Additional Costs to Budget For

The build cost is only part of the total spend. You will also need to budget for architect or engineer fees (typically 8 to 12 percent of build cost), planning permission (65 euro application fee plus drawings), building control compliance, kitchen fit-out if applicable (10,000 to 40,000 euro), landscaping and making good the garden, and temporary accommodation if the disruption is significant.

Always add a contingency of 10 to 15 percent to your budget. Extensions almost always uncover unexpected issues once walls are opened up, particularly in older homes.

Planning Permission

Many single-storey rear extensions up to 40 square metres are exempt from planning permission under current exempted development regulations. However, exemptions come with conditions around height, distance from boundaries, and total site coverage. Always check with your local authority or an architect before assuming your project is exempt.

How Long Does an Extension Take?

A straightforward single-storey rear extension typically takes 10 to 16 weeks from breaking ground to handover. Two-storey extensions take 14 to 22 weeks. Add 8 to 12 weeks for planning permission if required, and 4 to 8 weeks for design and tender.

Getting Quotes

The best approach is to have an architect or engineer prepare drawings and specifications before going to tender. This ensures every builder is pricing the same scope of work, making comparison meaningful. Get at least 3 quotes and check references for similar-sized projects.

Extension vs Moving: Which Makes More Sense?

Before committing to an extension, it is worth running the numbers on moving. In many cases, extending makes better financial sense, but not always.

When extending wins: If you love your neighbourhood, your children are settled in local schools, and you need one or two extra rooms, an extension is usually cheaper than the combined cost of selling (estate agent fees, legal costs, mortgage break fees) and buying (stamp duty, legal costs, moving costs, renovating a new property to your taste). A typical 30 to 40 square metre rear extension at 2,200 to 3,000 euro per square metre costs 66,000 to 120,000 euro, which in most areas is less than trading up.

When moving wins: If you need a fundamentally different type of home (detached instead of semi, larger garden, different area), or if your current property has structural limitations that make extending impractical (narrow site, poor orientation, shared walls on both sides), moving may be the more sensible option.

An architect can advise on what is feasible for your site, and a local estate agent can tell you what comparable properties are selling for. Make the decision based on real numbers rather than assumptions.

Common Extension Mistakes

Underestimating the budget. The build cost per square metre is just the starting point. Add 15 to 20 percent for professional fees (architect, engineer, quantity surveyor), planning application costs (65 to 80 euro for a domestic application), service connections, landscaping, and interior finishing. A 100,000 euro build budget should really start at 115,000 to 120,000 euro to be realistic.

Not hiring an architect. For any extension over 20 square metres, an architect will save you money in the long run through better design, fewer builder queries, and a smoother planning process. Compare architect quotes on QuoteHub.

Ignoring Part L (energy) regulations. All extensions must comply with current building regulations for insulation, glazing, and ventilation. This adds to the cost but also means your new space will be warm and energy-efficient. A BER assessment is required after completion. Visit HomeEnergyGuide.ie for details on energy requirements for extensions.

Not checking for exempted development. Rear extensions up to 40 square metres (subject to conditions) may be exempt from planning permission under SI 600 of 2001. However, the conditions are specific, including height limits, site coverage limits, and distance from boundaries. Get professional advice before assuming you are exempt.