Incomplete resistance; mould growth and built in furniture in a 1930’s Dublin clinker concrete apartment building.

Steady state and dynamic simulations tools based on current ISO standards play a crucial role in designing thermal envelopes that are robust and minimise risks of interstitial and surface condensation. These tools, when supplemented by environmental and material data from site, can be used to analyse building failure in a forensic way. In this case study issues of mould and surface condensation observed in 1930’s social housing apartments after a 1990’s service and fabric upgrade were investigated using ISO standards. The results show the roles of IWI, reductions in ventilation and the installation of cabinetry in impacting critical levels of surface temperature. Peer-review under the responsibility of the organizing committee of the ICMB23.


ISO
International Organisation for Standardisation IWI Internal Wall Insulation fRsi Temperature Factor CRA Condensation Risk Analysis Rsi/Rse Interior/Exterior Surface resistivity WUFI Wärme Und Feuchte Instationär Δ P Vapour pressure difference, inside to outside (Pa)

Introduction/Background
In the 1990's apartments in Dublin's Oliver Bond House were partially internally drylined with 38mm mineral wool and service alterations which reduced room ventilation.83% of respondents in a recent (2021) self-reported resident survey from this housing scheme confirmed having issues with damp and mould and 57.8% reported having been told that conditions were their fault and responsibility.These 396 apartments spread over 16 blocks in the city centre were constructed in 1938 of in situ cast 'Clinker' concrete, with external staircase and gantry access to each level Two case study apartments were selected for temperature and relative humidity monitoring, each a 2 bed, east orientated, mid floor unit with 2 working adult occupants..This study aimed to investigate the impacts of the partially applied IWI and reductions to ventilation.The study found that bespoke calculations for surface resistance (Rsi) were limited due to the linearisation of convective and radiative co-efficient values.Elevated values for Rsi in Austrian and German building codes [1] better reflected the impact of furniture and built-in units on surface temperature than those offered by EN 6946 [2] or EN 13788 [3].

Methodology
Site investigation, material and environmental data was applied to three standards, EN 13788, EN 10211 [4] (using Psitherm) and EN 15026 [5] (using WUFI).Internal Temperature and humidity data was used to calculate the fRsi.minand max values and the Humidity Class of the internal spaces.These Classifications were subsequently modelled in WUFI where the impact of differing levels of surface resistivity was also simulated.Thermal modelling software was used to calculate fRsi for the original and refurbished construction, comparing the impact of surface resistivity as well as the impact of modelling with measured versus calculated values.

Figure 2. (a) Humidity classification based on Delta P values in Apartment 205;
The fRsi.max results based on external climate data (Met Eireann) and recorded temperature and humidity for July-December showed different results for each apartment.The humidity class for all spaces was highly elevated, being either class 4 (e.g canteen/sports hall) or class 5 (e.g.brewery/laundry) illustrating the impact of reductions to the ventilation.These classes were incorporated into WUFI simulations but did not lead to critical levels of surface humidity.The thermal models revealed that in many locations the addition of IWI lowered the critical surface temperature and highlighted the impact of missing insulation, lack of IWI into reveals etc.Both WUFI and Psitherm modelling indicated the significant impact Rsi has on surface temperature.A mould risk was clearly identified in WUFI when combining the humidity class and elevated surface resistance and risk was confirmed in WUFI Bio for the internal surface of the IWI.Further site inspection confirmed the lowest internal surface temperatures were found at the back of wardrobes and around cabinetry, and a greater correlation between the measured/observed temperatures and thermal models was found where the 0.5 & 1.0 m 2 K/W values were used.
Table 1.Thermal model results showing impact of interior surface resistance on surface temperature, fRsi and u-value.

Conclusions
The installation of IWI lead to a lowering of critical surface temperatures and increased the risk of condensation and mould.Changes made by the landlord (to services/fireplace/boilers) and by the tenants (installing cabinets) have increased the internal moisture loads to critical levels.Rsi values offered by EN 13788 and EN 6946 did not properly account for the impact on built-in cabinetry on surface temperatures (and fRsi) as recorded and observed on site.Surface resistivity has greatest impact where thermal transmittance is high, in poorly insulated buildings so the impact of cabinetry should be considered more by designers in the areas of refurbishment and conservation, where currently fit out is not seen as impacting on fabric, being solely 'decoration'.This research also highlights the issue of giving advice on U-Value targets or limits as the calculations in figure 2 give significantly different U-Value results for the same wall build up using differing Rsi values only.

Figure 1 .
Figure 1.(a) photo of external access and external stair tower; (b) Thermal model through deck access, pre-refurb, showing ceiling temperature of 13.87°C.