Land and Site Assessment — What Decides a Site Is Buildable in Ireland

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When this matters most

You're still choosing sites, you've gone sale-agreed, or you've just inherited land and don't know if it's buildable.

When this doesn't apply

You already own a buildable site with full planning permission, tests done, and an engineer appointed.

Decision matrix

If: Site is outside the rural settlement boundary and never had planning

Then: Check the county development plan local-needs policy first. Rural housing policy tightened in most counties since 2022.

If: Site has planning permission but it's over 5 years old

Then: It may have lapsed. Check expiry date; renewal is rarely automatic.

If: Site has no public sewer within reasonable distance

Then: You need a Domestic Wastewater Treatment System (DWWTS) with percolation area. Get a percolation test before exchange of contracts.

If: Ground is rock, gravel, or sand (Class 1–2)

Then: Standard strip foundation likely. Cheapest foundation.

If: Ground is clay, silt, made ground (Class 3–4)

Then: Raft foundation likely. Add €15,000–€25,000 to budget.

If: Ground is peat, soft clay, or fill (Class 5+)

Then: Piled raft or driven piles. Add €40,000–€80,000.

Frequently asked questions

How much does a site assessment cost in Ireland?

€1,500–€4,000 for a soil test, percolation test, and water yield test together. Engineers typically charge €300–€600 for a desktop feasibility study on top.

What is a percolation test?

Measures how fast water drains into your soil. EPA Code of Practice sets minimum standards (e.g. T≤90 minutes for soil, ≤30 for subsoil); results dictate which wastewater system your site can take.

Can I build on a site with no planning permission?

Not in nearly any case for a one-off house. Some very limited agricultural and maintenance works are exempt under Schedule 2 of the Planning Regulations. Building a new dwelling is not exempt.

What is ribbon development?

A planning policy: building houses strung along a single rural road. Most county development plans refuse ribbon development outright. If your site is in a ribbon position, planning is very likely to be refused.

How deep does a borehole need to be for a private well?

Site-specific. Typical Irish domestic wells: 30–80 m deep. Yield (litres per minute) is what matters, not depth. Get an EIS test before purchase.

Is radon a problem on rural Irish sites?

Yes, particularly in the southeast (Co. Carlow, Wexford, parts of Wicklow). 1 in 10 Irish homes has elevated radon. Your engineer will specify a radon barrier and possibly a sump.

Sources

EPA, Code of Practice: Domestic Wastewater Treatment Systems (2018, updated 2021). https://www.epa.ie/publications/compliance--enforcement/waste-water/

Geological Survey Ireland, Irish Soil Classification System. https://www.gsi.ie/

Department of Housing, Rural Housing: Sustainable Rural Communities Guidelines for Planning Authorities 2020. https://www.gov.ie/