Hygrothermal risk assessment of retrofit of external insulated facade systems (EIFS) to non-traditional wall types in an Irish context using the glaser method and numerical modelling

Up to 80% of building failures can be attributed to moisture [1]. Failure in EIFS is usually due to moisture ingress at interfaces. The Irish Government seeks ambitious levels of EIFS retrofit but, to date, is not support this in guidance provided. An hygrothermal risk assessment of different EIFS on three non-traditional wall types, in Dublin, Belfast and Belmullet, was undertaken using transient numerical simulation and Glaser method calculations. Whereas the Glaser simulations show no risk, the transient numerical simulations show a significant impact of location, driving rain and the kind of physical failures that commonly occur. Cases with mineral wool and mineral render are low risk, most cases with acrylic render were high risk. The case for updating guidance to reflect the scale and urgency of the retrofit programme planned is clear.


Introduction and Aim
A UK white paper published in 2016 indicates that up to 80% of building failures are due to moisture [1].Large scale failures due to poorly-specified or -built EIFS retrofits have occurred in some countries.Related literature has indicated the main outcome to be excessive moisture ingress [2][3].

Methodological Approaches.
A review on the literature of building failures relating to moisture ingress through EIFS was conducted to establish the likely causes and extent of these failures.The guidance around hygrothermal risk assessment, including the updated code of practice BS5250:2021, was reviewed to establish how this is dealt with in Ireland, UK and further afield.Irish agrément certificates were reviewed and EIFS certificate holders were interviewed for their practice.
Initial numerical simulations were performed using WUFI Pro ® 6.5 in accordance with established modelling conventions [5,6].These were compared with the results of the Glaser method using Build Desk U ® 3.4 to compare results and establish if the Glaser method were appropriate.A parametric study was also undertaken, a selection of numerical simulations were stressed with 1% and 2% driving rain at different window positions to reflect potential water ingress.To increase the accuracy of the simulation results, some testing of the hygrothermal properties of a commonly-used block called 'no-fines' concrete block was undertaken.Some fully-tested material files were provided by an EIFS manufacturer.Both sets of material data were then input into the simulations.

Research Findings -EIFS failures and hygrothermal simulation
The findings from the research indicates that moisture-related failures in EIFS as installed occurs at the interfaces and junctions: window jambs and sills are particularly vulnerable.This can be attributed to a combination of a lack of design and assessment in the drawing office, and poor oversight and workmanship on site [3,4].Practical improvements were proposed.
The findings from the Glaser simulations indicated that 100% of cases passed the assessment.In the initial numerical assessment, where no joint failure at window jambs was allowed, the results indicate the risks are low risk cases, except for rendered block cavity walls where EPS insulation fills the cavity.Depending on the location, between 22-75% of these cavity wall cases were high risk.In more exposed climates driving rain leads to heightened moisture in the outer masonry leaf, which has difficulty drying to the relatively vapour tight layers of insulation enclosing it.
A further step was to parametrically assess the impact of joint failure at window jambs.Table 1, indicates that 40% of the cases on the mass concrete wall were high risk, 67% of the cases on the cavity wall were high risk and 50% of cases on the single leaf concrete block wall were high risk.In all cases studied, those with mineral wool and mineral render are all deemed low risk.Most of the cases with acrylic render are deemed high risk, as only one of 18 cases had the capacity to cope with moisture ingress.
This research has indicated that the use of the Glaser method for the hygrothermal assessment of EIFS cannot capture the extent of risk, especially when buildings are leaking.Figure 1.0 indicates a 30-year numerical simulation of three different EIFS retrofit cases, on the three wall types, as highlighted on Table 1.At least one of the three may need to be replaced after nine years as the moisture in the MW (with acrylic render), reaches moisture content (95% RH and rising) likely to lead to degradation and even spalling.The use of new virgin materials to potentially replace this EIFS system, before its expected life span [5], will increase carbon emissions which completely defeats the purpose of undertaking a retrofit designed to reduce carbon emissions.

Conclusions
This research has indicated that there are varying degrees of risk with EIFS retrofit.A "one size fits all approach" is not appropriate for the hygrothermal assessment of EIFS in most of the cases simulated.A more robust approach to hygrothermal assessment and guidance is required.The failure to do this may result in the replacement of significant EIFS systems before their expected life span has ended thus increasing carbon emissions and costs, defeating the purpose of undertaking this type of retrofit.

References
[1] May N, Sanders C. Moisture in buildings: an integrated approach to risk assessment and guidance 2016:31.

Table 1 .
Parametric Study Figure 1.WUFI Output Graph RH% at Centre of Insulation Layers -30yrs