Piled Raft Foundation in Ireland — For Peat, Made Ground, and Soft Clay Sites
On this page
Piled raft on Class 5+ ground: €280–€450/m². Piles transfer the load to a firm bearing stratum below the poor soil.
A piled raft foundation in Ireland is required when the soil near the surface cannot support the building. Piles are driven or bored to a firm bearing stratum, then a reinforced concrete slab caps them. €280–€450/m² of footprint. A 150 m² house: €42,000–€67,500. The site investigation (€1,500–€3,000) confirms the depth of poor soil and the bearing stratum. Engineer-led design is mandatory — piles must be designed and signed off by a chartered engineer with pile-driving experience. Common on infill sites in former bogs, made ground on reclaimed land, and any site with more than 2 m of soft clay or peat over rock. Building Regulations 2023 TGD-A (Structure) governs the structural rules.
When this matters most
Your site has Class 5+ ground (peat, made ground, fill) or significant fill that won't support a raft.
When this doesn't apply
Your site has Class 1–4 ground. A strip or raft is cheaper.
Sources
Building Regulations 2023, TGD-A (Structure). https://www.gov.ie/
Frequently asked questions
How much does a piled raft cost in Ireland?
€280–€450/m² of footprint. For a 150 m² house: €42,000–€67,500. Includes piles and the capping slab. Engineer design is mandatory.
When is a piled raft needed?
Class 5+ ground: peat, made ground, soft clay, fill. Common on infill sites in former bogs, reclaimed land, and any site with more than 2 m of poor soil over rock.
How deep are piles in Ireland?
Site-specific. Typically 4–15 m for residential. Driven piles are faster; bored piles are quieter. Engineer specifies depth based on the site investigation.
When this matters most
Your site has Class 5+ ground (peat, made ground, fill) or significant fill that won't support a raft.
When this doesn't apply
Your site has Class 1–4 ground. A strip or raft is cheaper.
Where to go next
Next decision
The next step in your build sequence.
- 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 →
- Raft Foundation in Ireland — The All-Rounder for Class 3–4 Ground and Subfloor Insulation →
- Subfloor Insulation in Ireland — PIR, EPS, or Mineral Wool, and What Part L 2022 Demands →
Branch into
Adjacent decisions at the same stage.
Watch out for
Common mistakes, hidden costs, gotchas.
- Foundation Cost by Soil Class in Ireland — The €/m² by Class 1 to Class 5+ →
- Foundation Gotchas in Ireland — The Six Things That Catch Self-Builders Off Guard →
- Radon Barrier in Ireland — Where It's Needed, What It Costs, and the Carlow-Wexford High-Risk Map →
- Strip Foundation in Ireland — When It Works, What It Costs, and What the Engineer Will Check →
Compare with
Alternative approaches worth knowing.