Hygrothermal risk assessment of external wall insulation retrofit to non-traditional wall types in an Irish context, using the Glaser method and a heat, air and moisture transient model

The Climate Action Plan 2019 targets the low-energy retrofit of 500,000 existing Irish homes before 2030.1 Up to 80 per cent of building failures can be attributed to moisture risks.2 The literature indicated that external wall insulation (EWI, ETICS) failures are mostly due to moisture ingress at junctions and interfaces. A hygrothermal risk assessment of EWI on three walls with rendered concrete/concrete blockwork/cavity walls in Dublin, Belfast and Belmullet was undertaken using transient numerical simulation and the Glaser method. The guidance, common practice indicates a preference for Glaser. The initial simulation results were compared to assess the appropriateness of Glaser. Material measurements were undertaken and this data was used in the transient numerical simulations. A parametric study was undertaken using a selection of the initial transient numerical simulations stressed with parameters of 1–2 per cent driving rain at different window positions. The results of the initial transient numerical simulations indicate that most retrofit cases, except on cavity walls, are low risk. All cases assessed using Glaser pass the assessments. The parametric study indicated between 40–67 per cent were high risk depending on the wall types. All cases with mineral wool/mineral render were low risk, while most cases with acrylic render were high risk. The research described in this paper indicates that using the Glaser method for hygrothermal assessment of EWI cannot capture the extent of the risk when buildings are leaking.