There is no single fixed national distance; the local authority's development plan and flood risk assessment requirements determine setbacks from a stream, and the planning authority will also consider access needed for maintenance and any arterial drainage or flood risk designations. Works within or near a watercourse can also require separate consent, so a hydrological or flood risk assessment is often needed.
Ireland does not have one uniform statutory setback distance that applies to every stream nationwide; instead, how close a house can be built depends on the local authority's development plan policies, the specific flood risk assessment for the site, and whether the watercourse is subject to any arterial drainage scheme or maintenance requirements under the Office of Public Works (OPW). Many development plans include a general policy requiring a buffer strip, commonly in the range of several metres, to be kept free of new buildings alongside rivers and streams, both to allow for maintenance access and to reduce flood and pollution risk, but the exact figure varies by council and by the watercourse's classification.
Under the national planning guidelines on flood risk (commonly known as 'The Planning System and Flood Risk Management'), local authorities must apply a sequential approach that steers new development away from areas at risk of flooding, and sites near watercourses often fall within flood zones that trigger a site-specific flood risk assessment as part of the planning application. This assessment considers the stream's flood extent, the effect of the proposed building on flood flow, and whether adequate mitigation, such as raised floor levels or a buffer setback, is achievable.
Separately, carrying out works in, under, or within a certain distance of a river or stream (such as culverting, bank works, or a new crossing) may require consent from the OPW where an arterial drainage scheme applies, or notification to the local authority under drainage or planning legislation, independent of the setback distance for the house itself.