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Digging out a basement

Digging a new basement under a house, or lowering an existing basement floor, costs €3,000 to €6,000 a m². It needs a structural engineer's design, usually underpinning, and often planning permission.

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  • €3,000 to €6,000a m² to dig and build
  • €50,000underpinning alone on one 60 m² basement
  • Engineerdesigns every dig-out
  • Planningusually needed for a new basement

How a basement is dug

  1. Investigation. Trial holes and a look at the foundations, the ground and the water table. The engineer designs the temporary support and the new walls.
  2. Permission. Planning, where it's needed, and a Commencement Notice to the council before work starts.
  3. Underpinning. The walls are supported in short sections, one pit at a time, so the house never loses its footing.
  4. Digging. Spoil leaves by conveyor and skip. Access for it is often the hardest part on a terrace.
  5. The box. Reinforced concrete walls and floor, waterproofing to BS 8102, drainage and a sump.
  6. Fit out. Light wells, stairs, insulation, ventilation, electrics and the finish.

Lowering an existing floor

Going deeper than the foundations means underpinning the walls. On one 60 m² basement lowered in Dublin 4, the underpinning alone cost about €50,000. Sometimes the foundations sit just below the old floor, and the floor can't be lowered all the way to the walls: a low ledge is left round the edge instead.

On a period house, talk to a conservation architect and a structural engineer before you talk to a builder.

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Questions we get asked

How much does it cost to dig out a basement in Ireland?

€3,000 to €6,000 a m² for the dig and the structure. The engineer's design and the ground decide where in that range it lands.

Do I need planning permission to dig a basement?

Usually, for a new basement. Ask the council, or apply for a section 5 declaration if you're not sure. See planning permission.

Can you dig a basement under a terraced house?

Sometimes, but it's the hardest case: shared walls, the neighbours' foundations and no side access for the spoil. An engineer's survey answers it.

Is it cheaper to add a basement when building a new house?

Yes. Digging an open site is far easier than working under a standing house. Self-builders can design the basement in from the start.

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