Foundation Gotchas in Ireland — The Six Things That Catch Self-Builders Off Guard
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Skip the soil test, ignore the radon, undercut the edge insulation, assume the slope is OK — six mistakes, six €10k+ fixes.
Six foundation mistakes that catch Irish self-builders: (1) skipping the soil test, leading to over- or under-spec'd foundations; (2) ignoring the radon barrier, which fails the BER test or the BCAR sign-off; (3) skipping the edge insulation, which costs 5–10% of the floor's heat loss; (4) under-spec'ing for a slope, leading to differential settlement; (5) not tanking on a high water table, leading to damp; (6) ignoring the build sequence, leading to access problems for the follow-on trades. Each mistake costs €10k–€30k to fix after the slab is poured. The site investigation (€1,500–€3,000) prevents all of them. Engineer-led foundation design is mandatory under BCAR (SI 9/2014). The Assigned Certifier signs off on the foundation before the walls go up.
TL;DR
Six common foundation mistakes: (1) skipping the soil test, (2) ignoring the radon barrier spec, (3) skipping the edge insulation, (4) under-spec'ing for a slope, (5) not tanking on a high water table, (6) no account for the build sequence.
Each mistake costs €10k–€30k to fix after the slab is poured. The site investigation (€1,500–€3,000) prevents all of them.
Engineer-led foundation design is mandatory under BCAR (SI 9/2014). The Assigned Certifier signs off on the foundation before the walls go up.
When this matters most
You're at foundation design stage or just before pouring the slab.
When this doesn't apply
The slab is poured and cured.
Frequently asked questions
What is the most common foundation mistake in Ireland?
Skipping the soil test. Without a test, the engineer is guessing. A €1,500–€3,000 test can save €10k–€30k in over- or under-spec'd foundations.
How much does it cost to fix foundation problems after the slab is poured?
€10,000–€30,000 for most common mistakes (under-spec'd foundations, missed radon barrier, no edge insulation). Some mistakes (e.g. piled raft needed but strip poured) cost €40,000+ to remediate.
Who signs off the foundation in Ireland?
The Assigned Certifier under BCAR (SI 9/2014). Inspects the foundation before the walls go up. Signs the Certificate of Compliance on Completion (CCC) at the end.
Sources
Building Control (Amendment) Regulations 2014 (SI 9/2014). https://www.gov.ie/
Frequently asked questions
What is the most common foundation mistake in Ireland?
Skipping the soil test. Without a test, the engineer is guessing. A €1,500–€3,000 test can save €10k–€30k in over- or under-spec'd foundations.
How much does it cost to fix foundation problems after the slab is poured?
€10,000–€30,000 for most common mistakes (under-spec'd foundations, missed radon barrier, no edge insulation). Some mistakes (e.g. piled raft needed but strip poured) cost €40,000+ to remediate.
Who signs off the foundation in Ireland?
The Assigned Certifier under BCAR (SI 9/2014). Inspects the foundation before the walls go up. Signs the Certificate of Compliance on Completion (CCC) at the end.
When this matters most
You're at foundation design stage or just before pouring the slab.
When this doesn't apply
The slab is poured and cured.
Where to go next
Branch into
Adjacent decisions at the same stage.