Freeze-thaw risk in solid masonry : are moisture reference years able to represent real climate conditions?

Today, there is no consensus on the selection method of representative exterior boundary conditions when performing HAM (Heat Air Moisture) simulations on building envelopes. Many existing methods to select moisture reference years (MRY) fail to provide an acceptable validation in terms of quantified risk assessment. Although new methods have been suggested during the past few years, the influence of several parameters on the selection of “critical years” in long-term datasets still needs to be assessed. The objective of this paper is to validate the application of MRY’s to evaluate freeze-thaw risk in retrofitted solid masonry. Furthermore, the influence of the chosen wall assembly, damage criterion, preconditioning and start date of the evaluation period on the ranking of critical years is assessed, using a 31-year meteorological dataset of Brussels. Results indicate that for a given wall assembly and freeze-thaw criterion, as well as a smart start date of the evaluated period, single year simulations entail a similar ranking of critical years as the corresponding year in the 31-year simulation. The number of critical freeze-thaw cycles only varies between 0 - 2 cycles (0 - 2.9%). However, changing the wall assembly and damage criterion, alters the top 5 ranking of critical years substantially

Freeze-thaw risk in solid masonry : are ‘hygrothermal response based‘ analyses mandatory when studying the sensitivity of building envelopes to climate change?

The 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) reports important evolutions in the climate system. These changes are likely to affect the durability of the built environment. Although many contemporary studies investigate the future energy efficiency of buildings, research on the impact of climate change on the hygrothermal behaviour and degradation of building envelopes is rather scarce. Using climate projections, we studied the advantage of ‘hygrothermal response based‘ analyses over ‘climate based‘ analyses when assessing the impact climate change on façades. This paper presents a sensitivity study on solid masonry wall assemblies, before and after internal retrofitting, using three RCP (Representative Concentration Pathways) projections of the ALARO-0 Regional Climate Model at the grid point of Brussels (BE). The findings suggest the necessity of a ‘hygrothermal response based‘ analysis to study the sensitivity of the building envelope to climate change. Moreover, the largest sensitivity is observed for RCP 8.5, the scenario having the highest projected greenhouse gas concentrations by the end of the century

Factorial study on the impact of climate change on freeze-thaw damage, mould growth and wood decay in solid masonry walls in Brussels

Previous studies show that climate change has an impact on the damage risks in solid masonry facades. To conserve these valuable buildings, it is important to determine the projected change in damages for the original and internally insulated cases. Since historical masonry covers a wide range of properties, it is unknown how sensitive the climate change impact is to variations in different parameters, such as wall thickness, brick type, etc. A factorial study is performed to determine the climate change impact on freeze-thaw risk, mould growth and wood decay in solid masonry in Brussels, Belgium. It is found that the critical orientation equals the critical wind-driven rain orientation and does not change over time. Further, the freeze-thaw risk is generally decreasing, whereas the change in mould growth and wood decay depends on the climate scenario. Knowing the brick type and rain exposure coefficient is most important when assessing the climate change impact. For freeze-thaw risk and wood decay, it is found that simulating one wall thickness for the uninsulated and one insulated case is sufficient to represent the climate change impact. Finally, the effects of climate change generally do not compensate for the increase in damage after the application of internal insulation

Decay of building facades may increase due to climate change

Building envelopes are sensitive to climate conditions. Changes to the climate conditions may alter the hygrothermal behaviour of building envelopes, and thus their performance in terms of deterioration. Therefore, it is important to assess the impact of climate change on damages in building envelopes. We performed 35.000 hygrothermal simulations of solid masonry walls over 10 locations across Europe. We included a range of parameter variations (e.g. masonry thickness, walls with/without interior insulation, brick type etc.). The climate change signal per location and damage mechanism results in a distribution, meaning that not all parameter combinations result in the same climate change signal. For example, there may be an increase in freeze-thaw damage for some parameter combinations, and a decrease for other combinations at the same location. Here, we presented the 90th percentile of the climate change signal. In this way, 90\% of the cases have a smaller or negative climate change signal. Based on the results, some damage risks are projected to increase, whereas others remain constant. Furthermore, the impact of climate change is not the same for different damage mechanisms and/or locations over Europe. Especially in the north of Europe, the risk on moisture-related damages is projected to increase. The results in this study are based on one model (i.e. the REMO regional climate model), and one scenario of projected greenhouse gases (i.e. RCP 4.5). Future studies should focus on more models and scenarios

Decision framework to select moisture reference years for hygrothermal simulations

The dominant degradation agent in facades is exposure to moisture. Damages resulting from long-term moisture exposure are typically evaluated through hygrothermal simulations. These simulations are computationally expensive. Therefore, a Moisture Reference Year (MRY), i.e. one year representing the moisture stress of the climate, is often used instead of simulating damages with the long-term climate itself. Usually, the methods to select MRYs were developed for specific wall types and damages. Up to now, no guideline exists to select one of these methods for particular cases. Therefore, we evaluated 21 existing MRY methods, and we developed a decision framework on how to select appropriate climate data for hygrothermal simulations. This paper presents the comparison between long-term simulations and simulations using MRYs for solid masonry walls in Brussels. The wall assemblies are analysed with and without interior insulation for 16 parameter variations each. A number of MRYs are able to represent the risk on freeze-thaw damage and wood decay, but the best performing MRYs vary between the different damages. Further, the decision framework consists of 5 levels, with each level requiring less computational power at the cost of its precision. It is recommended to perform long-term simulations whenever possible. Second best is to select an MRY with respect to a long-term simulation for a reference case. For large studies, a climate-based MRY accounting for the expected damage mechanisms could be considered as a first estimate of the results. In this study, the decision framework was successfully tested for solid masonry walls in Brussels

Decay of building facades may increase due to climate change

Building envelopes are sensitive to climate conditions. Changes to the climate conditions may alter the hygrothermal behaviour of building envelopes, and thus their performance in terms of deterioration. Therefore, it is important to assess the impact of climate change on damages in building envelopes. We performed 35.000 hygrothermal simulations of solid masonry walls over 10 locations across Europe. We included a range of parameter variations (e.g. masonry thickness, walls with/without interior insulation, brick type etc.). The climate change signal per location and damage mechanism results in a distribution, meaning that not all parameter combinations result in the same climate change signal. For example, there may be an increase in freeze-thaw damage for some parameter combinations, and a decrease for other combinations at the same location. Here, we presented the 90th percentile of the climate change signal. In this way, 90\% of the cases have a smaller or negative climate change signal. Based on the results, some damage risks are projected to increase, whereas others remain constant. Furthermore, the impact of climate change is not the same for different damage mechanisms and/or locations over Europe. Especially in the north of Europe, the risk on moisture-related damages is projected to increase. The results in this study are based on one model (i.e. the REMO regional climate model), and one scenario of projected greenhouse gases (i.e. RCP 4.5). Future studies should focus on more models and scenarios

A comprehensive framework to select climate data for hygrothermal simulations : application on solid masonry walls in Brussels

Moisture is a major agent of material degradation in building facades. The long-term degradation risks of building components are often evaluated by means of hygrothermal simulations for both new constructions as well as renovation. Due to the high computation load of these simulations, a Moisture Reference Year (MRY) (i.e. one year representing the moisture stress on the façade) is often used instead of simulating the long-term climate itself. In the past, a number of methods were developed to select MRYs, but they do not perform equally well for different wall types, materials, damage mechanisms etc. Today, a guideline to select an MRY method that is suitable for a specific study does not exist. Therefore, we developed a framework to select proper climate data for hygrothermal simulations. This paper presents the 5 levels of the framework, and its application on solid masonry walls in Brussels. The 5 levels account for the available resources, but result in a different level of detail. The optimal approach, yet computationally expensive, remains to simulate the long-term climate. Second best, an MRY is selected from one long-term simulation of a reference case, and that MRY is used in the remaining simulations. On the other hand, the ‘one-fits-all’ MRY needs the lowest computational requirements, but it is uncertain whether the ‘one-fits-all’ MRY actually represents the long-term moisture stress on the building. To conclude, the framework was successfully tested on solid masonry walls with and without interior insulation in Brussels