[en] Full text: In 2003, the Radiological Protection Institute of Ireland (R.P.I.I.) undertook the third of three localised radon surveys in Irish homes built since the introduction of the 1997 amending Building Regulations. Introduced in December 1997, these Regulations require that measures be taken at the construction stage to prevent the entry of radon into buildings from the underlying soil, and apply to buildings that commenced construction on or after the 1. July 1998. After Ennis (County Clare) in 2001 and Tralee (County Kerry) in 2002 (Synnott et al. 2004), the area selected in 2003 was the 10-km Irish National Grid Square containing Kilkenny City. As for the two previous surveys, this grid square is designated as a High Radon Area (where 10% or more of all houses are predicted to exceed 200 Bq/m3) and as such, all new homes which commenced construction after the introduction of the 1997 amending Building regulations are required to be fitted with a potential means to extract radon from the substructure (standby radon sump) and with an approved sealed membrane of low radon permeability over the footprint of the building (radon barrier). Between the three surveys, 247 homes were measured over a three-month period using Cr-39 passive alpha track detectors, 166 homes built since the amending Regulations came into force and 81 homes built in the immediate years prior to their introduction. Participating householders were also asked to complete a questionnaire to assess their awareness of the radon preventive measures included in their home at the time of construction. In all three surveys, the results indicate a clear a downward trend in the geometric mean between radon levels measured in new homes and in those built before 1998, between 30% and 50%. However, the results also highlight that the Building Regulations alone cannot guarantee that homes are adequately protected, as radon concentrations above the national Reference Level were found in homes built since 1998. The maximum radon concentrations measured in the Tralee and Kilkenny surveys were even found in the more recently built homes -including one home in Kilkenny with concentrations more than seven times the national Reference Level of 200 Bq/m³. The evaluation of householders awareness of radon preventive measures (questionnaire) showed that overall, between the three surveys, 40 to 45% and 20 to 37% of all respondents were unaware of the presence or absence of a radon sump or a radon barrier in their homes, respectively. Enhanced radon prevention guidance for new buildings was published by the Department of the Environment, Heritage and Local Government in October 2004 taking into account the recommendations made by the R.P.I.I. following the completion of these surveys, in particular the need for radon sump outlets to be clearly identified and radon levels to be assessed when the new dwelling is in use. (authors)