Conference Agenda

Use of wooden parts in the roofs is common practice for centuries, mainly as rafters or as wooden cladding or sheathing. With increase of energy performance of the roof, use of more and more insulation combined with air and vapor barriers more problems occur.

In last few years started the problems trying to use the evaluated structure of two ply pitched roof as single ply flat roof, which led to the complete decomposition of the sheathing and also to the rotting of wooden rafters. Lately, similar problem occurs also within the pitched roof. Common problem of these roofs is the ignorance of the layers with low water vapor permeability.

This paper deals with case study of the hotel pitched roof, which got huge amount of condensed water in short time and a family house with flat roof, where also wood degradation took part.

The required evaluation of building envelops parts is mandatory by the Slovak standard, but unfortunately lot of authorized engineer are not able to understand the results. Based on the experience from building survey, non-steady simulation in 1D Wufi Pro software was carried out. This confirmed the inappropriate composition, which need complete reconstruction of both roofs.

Surface coatings cannot wholly prevent water penetration and potential damage due to the fungal growth. The goal of the study was comparison of the impact of cracks in outer surface coatings on moisture content (MC) in window frames made of thermally modified (TM) and native Norway spruce comparing results of validated hygrothermal simulations in Delphin for Ljubljana with simulation results for Helsinki. The study also investigates the impact of the inner coating damage and compares results of different orientations of the installed window.

TM spruce has about 4 % lower MC content compared to native spruce in Ljubljana, whereas the calculated difference between both in Helsinki was approximately 3 %. For Ljubljana a 3 mm wide crack in native spruce coatings for the north orientation in Ljubljana poses significant moisture risks, while in Helsinki the upper border was calculated to be already at 1 mm. A 9 mm wide crack in the coatings of TM spruce remains within acceptable moisture content thresholds, even in the presence of coating damage for Helsinki climatic conditions.

For Ljubljana, analysis of the influence of size of inner cracks shows that maximal moisture content in the window profile is generally lower when cracks are present or even if the surface is uncoated. Comparison of different orientations of outside cracks on Norway spruce window frame in Ljubljana shows that for the similar moisture dynamics the crack may be about 2 mm wider on the south side. In contrast, for TM spruce, orientation was proven to be not as important.

Cross-Laminated Timber (CLT) is becoming increasingly popular for mid- and high-rise structures due to its structural and environmental benefits. Despite its advantages, the long-term durability of CLT, especially under wind-driven rain exposure, is a concern. Hygrothermal simulation is commonly used for assessing moisture performance; however, previous studies mainly focused on 1D simulation without considering rain leakage, which is one of the most significant moisture sources causing moisture damages. This study focuses on assessing the hygrothermal performance of 2D CLT connection under rain penetration loads. 2D DELPHIN model was created and validated against experimental data from a field study on a CLT wall in Vancouver. During the field tests, water was injected into the wetting pads placed on the CLT surfaces to simulate real-world rain penetration into the assembly. The model's accuracy was validated by comparing the simulated moisture contents (MCs) at the exterior and interior surfaces of the CLT with the actual measurements from the same locations. The simulation results were in good agreement with the experimental data, showing a mean absolute error (MAE) of 3% at 6 mm from the CLT exterior surface. The validated model was utilized to evaluate the hygrothermal performance of a CLT wall-floor connection under the extreme moisture reference year climatic conditions with rain penetration based on ASHRAE 160. 1% of WDR as the moisture load was deposited on the exterior layer of the CLT surface. Results showed a lower temperature at the floor level, with a MAE of 0.1°C and a maximum difference of 0.4°C compared to that at the wall level, while a higher MC at the floor level with a MAE of 0.14% and a maximum difference of 1%; consequently, a higher mould growth index at the floor level with a maximum difference of 0.4. Furthermore, the moisture levels simulated by the 1-D model exhibited a higher predicted value than those from the 2-D model at the wall level, resulting in a MAE of 0.4% and a maximum difference of 1%.

This study investigates the effect of hysteresis on hygrothermal performance of CLT walls under dynamic climate conditions, with a particular focus on high relative humidity (RH) levels and rainwater leakage. To achieve this, a hygrothermal model for building envelope materials was developed in Python, this model has incorporated hysteresis effect of building materials, solar radiation, and wind-driven rain (WDR) as a key environmental load. The model was validated using experimental data from an 18-month field study on a CLT wall in Vancouver. Without hysteresis, the simulated moisture content (MC) showed mean absolute errors (MAEs) of 0.37% at the exterior surface and 2.12% at the interior side of the CLT layer compared to the measurements. Incorporating hysteresis improved MC predictions, reducing the MAEs to 0.34% (exterior) and 1.85% (interior). Temperature and RH predictions were also well aligned with experimental data, although the inclusion of hysteresis had negligible impact on these parameters. Following validation, a one-year simulation under future climate conditions was conducted to assess the effect of hysteresis under dynamic climate conditions, with particular focus on rainwater leakage. Results indicated that hysteresis had minimal influence when rain penetration was absent. However, when rain leakage occurred, MC discrepancies increased, with the MAE rising to 2.40% and a maximum difference of 7.45% between simulations with and without hysteresis. These findings highlight the importance of considering hysteresis in hygrothermal modeling, particularly in scenarios where rainwater penetration is a critical factor.

Highly insulated external wall assemblies are commonly employed to enhance building energy performance. However, research indicates that these assemblies may lead to moisture-related issues, such as mould growth. Recent studies suggest that the use of highly hygroscopic insulation materials, owing to their higher moisture buffering capacity, may mitigate relative humidity levels and consequently the risk of mould growth. This study investigates the effects of such insulations on mould growth and heat flux through probabilistic hygrothermal simulations. Four insulation types—EPS, mineral wool, wood fibre, and cellulose—are analysed under Stockholm’s climatic conditions. The probabilistic analysis accounts for uncertainties in material properties and boundary conditions, evaluating key parameters on wooden studs, including mould growth, relative humidity, moisture content, and heat flux through insulation layers. Results reveal that high moisture buffering capacity alone does not necessarily enhance resistance to mould growth. Instead, combination of that with other hygrothermal functions emerges as a critical factor. Additionally, increased moisture content in insulation layers correlates with elevated heat flux, thereby reducing the wall assembly’s energy performance. These findings illustrate the necessity of balancing moisture safety, durability, and thermal performance to optimise the design of insulated wall assemblies.

Energy efficiency in the building sector is crucial for reducing environmental impact, with improving the performance of existing buildings being a key focus. A significant strategy involves minimising thermal losses through walls, which is particularly challenging in the retrofitting of historic buildings where external insulation is often impractical due to listed façades. Internal insulation systems offer a solution but must be carefully designed to avoid issues such as moisture accumulation, mould growth, and material degradation. One approach to moisture control is the use of vapour retarders, membranes installed on the interior side of the wall. Among these, smart vapour retarders (SVRs) have shown promise due to their ability to block vapour flow in winter while allowing drying in summer. However, despite their potential, the current knowledge on SVRs remains incomplete and their application in internal insulation systems deserves further investigation.

This study addresses the influence of climate, wall construction, orientation, and indoor conditions on the hygrothermal performance of brick walls with internal insulation and vapour retarders. The aim is to identify scenarios where SVRs are particularly beneficial by varying the parameters which have relevant impact on the wall´s hygrothermal performance. To achieve this, 20,000 configurations are investigated by means of hygrothermal simulation with the software Delphin (Bauklimatik Dresden). The mould growth index behind the insulation is investigated by comparing systems presenting constant and variable vapour retarders with diffusion-open systems. Different insulation materials, such as mineral wool, blown cellulose, expanded polyurethane and calcium silicate are investigated.

The findings reveal that vapour retarders improve performance across all scenarios compared to cases without retarders. SVRs demonstrate particular effectiveness in climates characterised by significant rainfall and moderate temperatures, such as continental and maritime ones. Internal conditions were found to exert a significant influence on wall performance, underscoring the need for case-specific designs. The results highlight that the selection of vapour retarders must consider the unique requirements of each application, offering guidance for their effective integration into retrofitting projects.

This study contributes to a deeper understanding of SVRs’ performances, providing valuable insights for enhancing the energy efficiency and durability of retrofitted historic buildings.