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Do I need attenuation for a new house in Ireland?

It depends on the site and the local authority. A single house on a rural site with good percolation often manages run-off entirely by infiltration, while a house connecting to a surface water sewer, or on poorly draining ground, may be required by planning condition to attenuate run-off and restrict the discharge rate.

Attenuation requirements come from two directions: building regulations require adequate surface water drainage, and planning authorities apply development plan SuDS policies through conditions on permissions. Where a condition specifies a maximum discharge rate, some form of storage is usually needed to achieve it.

The practical test is whether the ground can absorb the run-off. Where percolation testing shows good infiltration and there is space clear of foundations and percolation areas, a soakaway may be sufficient on its own. Where it cannot, attenuation with flow control is the standard alternative.

Deciding the surface water strategy

  • Check the planning conditions attached to your permission
  • Check the local authority development plan and any SuDS guidance
  • Carry out percolation testing for infiltration feasibility
  • Identify the available outfall — sewer, watercourse or ground
  • Have the engineer size storage and flow control for the design storm

Sources

Last reviewed 25 August 2026. General information only — not legal or planning advice.

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