High fertility rates, a younger population and a resulting high share of households with children were important factors explaining Ireland’s larger households.

Ireland has had a high average household size for 20 years and has had the largest average household size among the countries studied every year since 2011.

A group of countries with higher household sizes included Ireland, Spain, Portugal and Greece.

Between 2005 and 2011, Ireland’s household size declined. However, that decline has stalled in the decade between 2011 and 2021.

“Household Size in Ireland: Stylised Facts and Cross-country Trends” was co-authored by ESRI associate research professor Dr Conor O’Toole and ESRI research officer Dr Rachel Slaymaker. The research was funded by the Department of Housing.

Dr O’Toole said: “Ireland has a greater number of persons per household relative to other European countries mainly due to a younger population. As the population ages, household size is likely to decline once sufficient, and suitable, housing is available.”

He said Ireland’s younger population “naturally drives” household size higher than in other countries.

“There are other differences, from the level of educational attainment to the length of time people are spending in education. You have differences in cohabitation or marital status across countries,” he said.

“The economic factors we’re looking at are unemployment and income. Factors that might affect the change in household size are things like credit market access, the cost of credit or the housing supply.”

According to the report, while Ireland continues to have a high birth rate and a younger population compared to other countries, it will continue to have a higher average household size.

Though the report found an increase in housing supply would reduce average household size, the reduction caused by factors including ageing, marital status and number of children would far outweigh any reduction brought by additional housing.