Choose Your Foundation — Your Engineer Picks, Your Soil Decides, Your Budget Pays
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When this matters most
You're at detailed design and need to commit to a foundation type. Or you're existing stock and considering subfloor replacement.
When this doesn't apply
Foundation is already poured and cured. You're in stages 6+ of this site.
Decision matrix
If: Soil is Class 1–2 (rock, gravel, dense sand)
Then: Strip foundation. €120–€180/m² footprint.
If: Soil is Class 3–4 (firm clay, silt, sand with clay)
Then: Raft foundation. €180–€260/m².
If: Soil is Class 5+ (peat, soft clay, made ground, fill)
Then: Piled raft or driven piles. €280–€450/m².
If: Site is sloped >2 m across footprint
Then: Stepped strip or raft with retaining. +€40–€80/m².
If: Site has a high water table
Then: Raft with water management + tanking. +€30–€60/m².
If: Radon is high (Co. Carlow, Wexford)
Then: Add radon barrier and sump. +€8–€15/m².
Frequently asked questions
How much does a foundation cost per m² in Ireland?
€120–€450/m² of footprint depending on soil class. A 150 m² house on a strip foundation = €18,000–€27,000; piled raft on the same footprint = €42,000–€67,500.
Do I really need a soil test?
Yes. Without it your engineer is guessing, and you're carrying the risk. €1,500–€3,000 for the test can save €30,000–€60,000 in over-spec'd or under-spec'd foundations.
What is a raft foundation?
A reinforced concrete slab that spreads the building load across the entire footprint. Cheaper than piling for moderate soils; faster than strip+wall for variable soils. Most BER A1 self-builds use raft because of subfloor insulation integration.
What is a piled raft?
Piles driven or bored to firm bearing strata, then a reinforced concrete slab capping them. Required when soil near the surface cannot support the building.
Do I need a radon barrier?
Yes, on every new build in Ireland since 1998. Most are a 1,200-gauge polythene membrane. In high-radon areas (Carlow, Wexford) add a radon sump and extract fan.
Sources
Building Regulations 2023, Technical Guidance Document A (Structure), Department of Housing. https://www.gov.ie/
Irish Geological Survey, Irish Soil Classification System. https://www.gsi.ie/
Related guides
- Foundation Cost by Soil Class in Ireland — The €/m² by Class 1 to Class 5+
- Foundation Depth in Ireland — 900 mm, 1.2 m, or Below Frost Line
- Foundation for a Timber Frame House in Ireland — Raft Is the Standard
- Foundation Gotchas in Ireland — The Six Things That Catch Self-Builders Off Guard
- Piled Raft Foundation in Ireland — For Peat, Made Ground, and Soft Clay Sites
- Radon Barrier in Ireland — Where It's Needed, What It Costs, and the Carlow-Wexford High-Risk Map
- Raft Foundation in Ireland — The All-Rounder for Class 3–4 Ground and Subfloor Insulation
- Strip Foundation in Ireland — When It Works, What It Costs, and What the Engineer Will Check
- Subfloor Insulation in Ireland — PIR, EPS, or Mineral Wool, and What Part L 2022 Demands
- Suspended vs Solid Floor in Ireland — Timber Suspended, Solid Slab, or Beam-and-Block