Quantifying overheating in nZEB Irish residential buildings. An analysis of recorded interior temperatures of Irish newbuild and retrofit residential buildings against CIBSE, Passive House and WHO overheating criteria and recorded occupant satisfaction

The prevalence of overheating is presented based on monitored indoor temperatures in 50 Irish low-energy nearly Zero Energy Buildings (nZEB), including 37 passive houses (PH) across rural, town and urban settings and seven typology groupings. Objective overheating standards were used; (i) CIBSE TM59, (ii) Passive House (PH) and (iii) World Health Organisation (WHO) in addition to Occupant Satisfaction Surveys (OSS) and interviews. For newbuilds, 26% overheated according to CIBSE TM59 (required by Irish Building Regulations) and 48% of average temperatures exceeded WHO recommendations at least 10% of the year, and 20% for more than 20% of the year. Only 4% of new PH's failed the PH criteria and only 5% of retrofit failed CIBSE TM59. Some residences failed CIBSE yet passed PH overheating criteria (and vice versa), due to the divergence between the ‘room by room’ analysis of overheating (CIBSE and WHO) compared with building-wide criteria (PH), especially in bedrooms. Poorly installed/commissioned heat pumps and lack of control e.g. little external shading and window restrictors impeded occupants regulation of overheating. A focused national strategy on overheating is recommended given the unprecedented national transformation towards nZEB homes (including at-risk apartments), especially in the context of the warming climate and aging population.