Contingency Budget for a Self-Build in Ireland — Why 10% Is the Minimum and 15% Is Safer
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10% contingency is the minimum. 15% is safer. Covers rotten steel, soil surprises, upgrade costs, VAT miscalculations.
10% contingency is the minimum (€45k–€68k on a 180 m² house). 15% is safer. Covers rotten steel in the foundation, soil surprises, upgrade costs, VAT miscalculations, weather delays, and the unknown unknowns. Most self-build cost overruns are site-specific (€20k+ on slope, access, services) and client-driven (€5k–€15k on upgrades mid-build). Hold the contingency in a separate account. Don't spend it on upgrades without thinking. It's there for the unforeseen. Most self-builders who finish on budget credit the contingency for any surprise; those who don't have the cash to absorb the surprise.
TL;DR
10% contingency is the minimum (€45k–€68k on a 180 m² house). 15% is safer. Covers rotten steel, soil surprises, upgrade costs, VAT miscalculations.
Most self-build cost overruns are site-specific (€20k+ on slope, access, services) and client-driven (€5k–€15k on upgrades mid-build).
Hold the contingency in a separate account. Don't spend it on upgrades without thinking. It's there for the unforeseen.
When this matters most
You're shaping the budget envelope.
When this doesn't apply
The build is finished and the retention is released.
Frequently asked questions
How much contingency do I need for a self-build?
10% of build cost is the minimum. 15% is safer. For a 180 m² house: €45k–€68k (10%) or €68k–€103k (15%).
What does contingency cover?
Rotten steel in the foundation, soil surprises, upgrade costs, VAT miscalculations, weather delays, and the unknown unknowns. Most self-build cost overruns are site-specific and client-driven.
Where should I hold the contingency?
In a separate savings account. Don't mix it with the build budget. Don't spend it on upgrades without thinking — it's there for the unforeseen.
Sources
SCSI, Construction Cost Guide 2026. https://www.scsi.ie/
Frequently asked questions
How much contingency do I need for a self-build?
10% of build cost is the minimum. 15% is safer. For a 180 m² house: €45k–€68k (10%) or €68k–€103k (15%).
What does contingency cover?
Rotten steel in the foundation, soil surprises, upgrade costs, VAT miscalculations, weather delays, and the unknown unknowns. Most self-build cost overruns are site-specific and client-driven.
Where should I hold the contingency?
In a separate savings account. Don't mix it with the build budget. Don't spend it on upgrades without thinking — it's there for the unforeseen.
When this matters most
You're shaping the budget envelope.
When this doesn't apply
The build is finished and the retention is released.
Where to go next
Watch out for
Common mistakes, hidden costs, gotchas.