Foundation design has to be based on the actual ground conditions, so some form of ground investigation is effectively necessary for every house. On rural sites using an on-site wastewater system, a site characterisation and percolation test carried out to the EPA Code of Practice is a separate and specific requirement of the planning process.
Two different kinds of soil testing come up in Irish house projects and they are often confused. Geotechnical testing establishes soil strength and groundwater for foundation design, and supports compliance with Part A of the building regulations. Percolation testing, part of a site characterisation carried out to the EPA Code of Practice, establishes whether the ground can accept treated effluent from a wastewater treatment system.
A planning authority will normally require the site characterisation report with the application where an on-site wastewater system is proposed. Geotechnical investigation is not usually a planning requirement, but the designer and assigned certifier need it to design and certify the foundations.