Scenario-based approach for the determination of the advantages of the combined carbon and seismic retrofitting strategy
Abstract:
This Master Thesis focused on the comparison of different scenarios for the renovation of existing buildings and the demonstration of the environmental benefits of a combined energy and seismic retrofitting strategy. This scenario-based approach comprised the investigation of seven different scenarios for a case-study, existing unreinforced masonry building located in the city of St. Gallen in Switzerland: the preservation of the building as it is, the demolition and reconstruction of the building, the energy renovation of the building, the carbon renovation of the building, the seismic retrofit of the building, the combined seismic and energy retrofit of the building using conventional materials and the combined seismic and energy retrofit of the building using bio-based materials, comprising timber beams and straw infill panels. A parametric LCA analysis led to the determination of the bio-based combined seismic and energy retrofitting solution comprising timber beams and straw infill panels as the solution corresponding to the highest environmental performance for the building, followed by the the carbon renovation of the building. The major part of the research was the LCA analysis to prove the benefits of the combined retrofitting strategy. The calculations were obtained both manually as well as parametrically with use of Bombyx plugin for Grasshopper in Rhino. On the other hand a simplified nonlinear static analysis procedure was followed to assess the seismic performance of the existing, case-study building. This simplified, force-based in-plane seismic analysis indicates a high seismic performance for the un-retrofitted case-study building. This is attributed to the low seismicity of St. Gallen, the low seismic mass of the building, comprising light timber floor diaphragms, and the thick high-strength brick masonry walls of the building. However, only the in-plane seismic behavior of the building was investigated in this Master Thesis. Moreover, this Master Thesis focused on the force-based seismic assessment of the building and did not include any displacement-based analysis.
The Climate Change and need for increase in renovation rates:
The impact of climate change is inevitable where the global temperature rises are inducing shifts in the earth’s geological dynamics, leading to higher frequencies of earthquakes and volcanic activity (Masih, 2018).Consequently, numerous methodologies are being developed and adopted to mitigate the escalating adverse impacts of climate change. One such approach is the Climate Target Plan 2030, which necessitates an effort within the European Union (EU) to achieve a 60% reduction in Greenhouse Gas (GHG) emissions from the building sector (Commission, 2020b). In Switzerland, the housing sector accounts for 25% of environmental impacts, positioning it as the most significant contributor alongside the food and nutrition (FOEN, 2022). Thus, immediate measures must be implemented to realize the objective outlined by the Federal Council, including halving the emissions by 2030 and achieving net zero GHG emissions by 2050.
Despite the continual construction of new buildings each year, it is crucial not to underestimate the significance of existing structures. In EU, approximately 90% of the building were constructed before 1990s, with the annual rate of the new construction standing at mere 1% (Economidou et al., 2011). Given that 75% of the EU building stock is allocated to the residential sector, it is evident that significant portion of the residential properties have aged and are in need of updates to align with current standards (Pohoryles et al., 2020).
Retrofitting buildings with focus on energy and material efficiency represents means to enhance urban systems, which are crucial for the reduction of emissions and development of climate resilience (Lee et al., 2023). Consequently, a concentrated effort is needed to increase the renovation rate of existing buildings, particularly those constructed during periods with outdated regulations or when seismic standards were non-existent.
Retrofit/renovation opposed to demolition:
There are two primary approaches to managing old buildings: updating their condition or demolishing them and constructing anew. When considering improving the condition of a building, two potential approaches are renovation and retrofitting, with retrofitting involving more extensive modifications to existing structures and systems. Retrofitting aims to prolong the lifespan of a building by altering its physical, functional, architectural and ecological attributes (Scuderi, 2019). Conversely, in renovation strategies for older buildings, energy renovation is often employed to enhance their energy performance. The positive effects of energy renovation, including system replacement and facade insulation, have been recognized for their significant benefits in reducing both Life Cycle Environmental Impacts (LCEI) and Life Cycle Costs (LCC) (Galimshina et al., 2020). On the other hand, demolition involves the complete dismantling of a building followed by reconstruction. Given that 33% of EU waste originates from demolition and construction activities, this approach should be avoided whenever possible (Belleri and Marini, 2016). Additionally, during demolition or decomposition of materials, carbon stored in building components is released back into the atmosphere, resulting in considerable environmental impacts (Göswein et al., 2020). Therefore, demolition should only be considered in cases where a building is in an extremely poor condition and retrofitting or renovation is neither economically nor technically feasible (Margani et al., 2020).
Request for combined retrofitting strategy:
Globally, 39% of emissions come from the construction sector (WGBC, 2019). Currently, only 1% of renovated buildings in the EU undergo energy renovation, with an additional 0.2% significantly reducing their energy consumption (Commission, 2020a). In Switzerland, the operation of buildings accounts for 24% of emissions with 55% attributed to fossil fuel heating system (Priore et al., 2023). Consequently, the combination of high emissions from the sector, low renovation rates and poor energy performance pose challenges to realizing the objectives of the European Green Deal and the 2050 Swiss Energy strategy (Pohoryles et al., 2020;Priore et al., 2023). Traditionally, the prime focus of renovation efforts has been on reducing the energy demand of buildings. Common strategies include facade renovation, upgrading of windows and replacement of building systems with a goal of eliminating the fossil heating systems (Margani et al., 2020). However, concentrating simply on energy demand reduction may not address potential building vulnerabilities to natural hazards such as earthquakes, which are of particular interest for this study. Renovation efforts solely aiming at energy reduction may underestimate not only potential social and economic losses, but also environmental impact resulting from embodied Carbon Dioxide (CO2) emissions associated with seismic risks (Marini et al., 2022). Hence, the primary focus and intention of this research lied in identifying an optimal renovation strategy that simultaneously improves energy and seismic performance while striving to minimize environmental impacts.
Scenario-based approach:
For the research the following scenarios presented in figure 1 were chosen based on prevalent energy renovation and seismic retrofitting methodologies, with the goal of covering all feasible strategies for upgrading existing buildings. Different solutions were assessed according to the complexity of each scenario.
figure 3: solution 1
figure 6: solution 4
The literature findings highlight the significance of system replacement and facade insulation when aiming for improvement of energy efficiency of a building. It also reveals the critical roles played by the selection of system types and insulation materials in reducing carbon emissions (Galimshina et al., 2020, 2021, 2022). Therefore, the solutions for the five scenarios were carefully constructed to take into account all possible actions and their combinations when aiming to improve the existing building.
The main difference is in the selection of materials for the insulation of the building, in the replacement of the existing heating system (which in this case was an oil boiler), the replacement of windows and whether or not the seismic performance will take place.
For the system replacement in this research in the scenarios and their solutions where heating systems are replaced, the air-to-water heat pump was chosen due to its superior Life Cycle Assessment (LCA) results. Moreover, one more aspect that influenced this decision is the scarcity of timber for meeting the energy demand of the Swiss building stock with timber pellet boilers (Galimshina et al., 2022). For that reason timber pellet boilers was not selected for application in this research and instead air-to-water heat pumps were selected.
In the research the assumption was made, based on the literature review, that the bio-based insulation, in this case straw would have significant benefits since products such as timber, hemp and straw contain around 50% of carbon by dry mass. This is the percentage of the carbon present in these organic substances after removal of all the moisture. This resembles the potential for carbon storage to occur in buildings made from these materials. The amount of straw grown in EU is identified as sufficient for covering the needs for use in the building stock and with its application, 3% of the GHG emissions can be stored in the building envelope (Göswein et al., 2020; Pittau et al., 2019). Due to its fast growth, straw has high potential to sequester carbon through photosynthesis (Arehart et al., 2021). Therefore, due to the high availability and environmental benefits of this material, straw insulation was selected as a bio-based insulation option in the analysis.
Combining energy and seismic renovation has been introduced recently and some of the approaches that were already established are textile-reinforced mortar (Bournas, 2018) and exoskeletons (D’Urso and Cicero, 2019) for the safety and structural improvements. However, these approaches are based on materials of high environmental impact. In an attempt to decrease the environmental impact associated with the materials used in the existing seismic and energy retrofit solutions, this study focuses on the use of bio-based materials of low environmental impact, such as timber, for the seismic retrofit of existing buildings.
New construction life-cycle and embodied emissions
When discussing demolition and new construction, this implies that the existing building has reached the end of its life. Consequently, in such case, the embodied emissions associated with the replacement and disposal of the existing structure were added to the total embodied emissions of the new building. A representation of this principle can be seen in the fig. 12.
figure 4: solution 2
figure 7: solution 5
figure 8: solution 6
The existing single-family house was thoroughly analyzed. The exterior walls above ground level held utmost significance as retrofitting measures were focused on them. The structure consisted of a double masonry wall with only 5cm of insulation in the facade. The underground walls remained unaltered, as the renovation efforts prioritized enhancing the building envelope without necessitating extensive construction or disturbance to residents.
In all of the analyzed scenarios and their solutions, the exterior walls were updated to meet the SIA standards for the new construction. Where depending on the solution the concrete and conventional (EPS) insulation or timber and bio-based (straw) insulation were used along with preservation or replacement of the oil boiler to air-to water heat pump.
LCA analysis:
For all of the solutions a separate file was developed which used Bombyx for LCA with Hive for energy calculations. In the file the layers were taken from the created Rhino building model. These layers were later on used to extract areas and geometry information required for the analysis. Subsequently, building components were defined layer by layer, with U-values and LCA properties initially obtained for each component (such as exterior walls, interior walls, floor, roof, etc.). Embodied emission calculations were then performed by aggregating these properties, resulting in the total embodied emissions for the entire building. Regarding operational emissions, the first step involved selection of necessary information for the Hive analysis, including weather files, context, building geometry, windows and shading. Following this, the heating system was defined and electricity source selected, enabling the calculation of heating, cooling and electricity demands, which were then used to derive operational emissions. Finally, the embodied and operational emissions were combined to provide an overview of the total emissions for each solution.
figure 10: parametric LCA
It is important to understand the necessary manual adjustments that were made for the embodied emissions calculations obtained from the LCA analysis in Bombyx. Since in Bombyx the total emissions are considered in all solutions, these had to be readjusted to resemble the real situation. What this entails is that in the case of new construction (solution 2), the embodied emissions resulting from the replacement and end-of-life of the existing structure were included in the embodied emissions calculations. Conversely, for all other solutions involving renovation and combined retrofitting measures (solutions 3-7), the embodied emissions of the existing structure were subtracted from the total embodied emissions. This manual adjustment was necessary to isolate the impact of only the added materials in the facade.
Existing building life-cycle and embodied emissions
In the figure 11 an overview of the life-cycle consideration of the existing single-family house is presented. The typical 60 years period was taken into account where in the first step, at the beginning, the embodied emissions of the existing structure were considered as resulting emissions from the extraction, manufacturing, transportation and installation processes of the construction materials. At the end-of-life of a building, in this case at year 60, there would be embodied emissions resulting from the disposal or recycling of previously used construction materials.
LCA operational emissions adjustments
Given that this research primarily concentrated on the heating system replacement and did not include the use of photovoltaic (PV) systems as renewable energy sources for electricity production in the analysis, only the operational emissions stemming from the heating systems were taken into consideration. Another rationale behind this decision was that within Bombyx, the operational emissions of heat pumps already included the electricity required for their operation, as it was integrated into the calculation of operational emissions for the chosen systems. Therefore, when a heat pump was selected as the heating system and consumer mix was used as the electricity source, there was a potential for double counting of electricity usage, which led to elevated operational emissions. In contrast, for heating sources such as oil boilers that rely on external sources, in this case oil, for their operation, double counting did not occur because the emissions from the oil were considered in the analysis. Therefore, to mitigate potential issues of double counting for heat pumps, only the values for operational emissions from the heating systems were considered and were used for the LCA analysis.
figure 11
figure 12
Retrofit without window replacement
In solutions involving carbon renovation, seismic retrofit, or combined biobased retrofitting without window replacement, the following principle in fig. 13 was employed for calculating embodied emissions. Hereby we are referring to solutions: 4, 5 and 7. Since Bombyx provided total embodied emissions, it was necessary to subtract the embodied emissions of the existing structure from the calculated total embodied emissions. Therefore, the following principle was used: corrected embodied emissions= total embodied in Bombyx - (GHG embodied + GHG replacement + GHG EoL of all building components) For all building components the stated emissions were summed, and in the last step subtracted from the total embodied emissions calculated in Bombyx
figure 13
figure 14
figure 9: solution 7
figure 1
figure 2
Retrofit with window replacement
In energy renovation solutions (3.1 & 3.2) and conventional combined retrofitting solutions (6.1 & 6.2) the same principle was applied as presented in figure 13. The major difference is that, since in these cases the windows were replaced, the replacement and end-of-life emissions associated with windows were subtracted from the sum of embodied, replacement and end-of-life emissions of all the building components. The principle used was therefore: corrected embodied emissions = total embodied in Bombyx - ((GHG embodied + GHG replacement + GHG EoL of all building components except windows)- (GHG replacement + GHG EoL of new windows)) In the last step the obtained number was subtracted from the total embodied emissions calculated with Bombyx for the solution.
figure 5: solution 3
LCA analysis:
It all begins with an idea. Maybe you want to launch a business. Maybe you want to turn a hobby into something more. Or maybe you have a creative project to share with the world. Whatever it is, the way you tell your story online can make all the difference.
Total emissions (kgCO-eq/m2a)
figure 15
Biogenic carbon (kgCO-eq/m2a)
figure 16
Biogenic carbon:
The biogenic carbon content was 13% higher in Solution 7 compared to Solution 4. This difference was primarily be attributed to the presence of structural timber beams in Scenario 7. Due to the greater amount of timber used in solution 7 compared to solution 4, and the higher biogenic carbon potential of timber as defined in the KBOB database compared to straw, this led to better performance for solution 7 regarding the result of lower embodied emissions. However, it is noteworthy that the approach used for the calculation in Bombyx is the -1/+1 approach which underestimates the crop rotation period.
Conclusion:
Sine my personal interests lie in the LCA analysis and as it was the major part of the thesis, I would hereby focus on the conclusion relating to the Life Cycle Assessment analysis. The aim of this Master Thesis was the comparison of different scenarios for the renovation of existing buildings and the demonstration of the environmental advantages of a combined energy and seismic retrofitting strategy compared to other commonly used renovation scenarios. Seven different scenarios have been investigated for a case-study, existing unreinforced masonry building located in the city of St. Gallen in Switzerland: the preservation of the building as it is, the demolition and reconstruction of the building, the energy renovation of the building, the carbon renovation of the building, the seismic retrofit of the building, the combined seismic and energy retrofit of the building using conventional materials and the combined seismic and energy retrofit of the building using bio-based materials, comprising timber beams and straw infill panels. The bio-based combined seismic and energy retrofitting solution (Solution 7) comprising timber beams and straw infill panels led to the lowest environmental impact, according to the results of a parametric LCA analysis. The second best option with respect to the minimization of environmental impact was the carbon renovation of the building (Solution 4). The goal of using the Bombyx tool for early design parametric LCA was proven correct through its adoption in this case study where the results were double checked manually. This reveals the benefits of using the parametric tool for assessment. However, one issue could be the fact that the parametric LCA implies the -1/+1 static method. Even though the variations between this and semi-static method do not seem to vary greatly, it would be advisable to consider dynamic LCA for more detailed analysis. This could be the next step in the analysis process after the narrowing of the options through parametric LCA. Implementation of dynamic approach is important as for the fast-growing bio-based materials, such as straw, the positive radiative forcing at the year 0, due to production and construction, would immediately reach negative value in the first year due to the one year regrowth period. On the other hand, the average period for forests to regrow can be considered to be approximately from 40 to 90 years.
List of the mentioned references:
Arehart, J. H., Hart, J., Pomponi, F., & D’Amico, B. (2021). Carbon sequestration and storage in the built environment. Sustainable Production and Consumption, 27, 1047–1063.
Belleri, A., & Marini, A. (2016). Does seismic risk affect the environmental impact of existing buildings? Energy and Buildings, 110, 149–158.
Bournas, D. A. (2018). Concurrent seismic and energy retrofitting of RC and masonry building envelopes using inorganic textile-based composites combined with insulation materials: A new concept. Composites Part B: Engineering, 148, 166–179.
Commission, E. (2020a). A renovation wave for Europe—Greening our buildings, creating jobs, improving lives. Communication from the European Commission to the European Parliament, the Council, the European Economic and Social Committee, and the Committee of the Regions.
Commission, E. (2020b). Stepping up Europe’s 2030 climate ambition: Investing in a climate-neutral future for the benefit of our people. J. Chem. Inf. Model, 53(9), 1689–1699.
D’Urso, S., & Cicero, B. (2019). From the efficiency of nature to parametric design: A holistic approach for sustainable building renovation in seismic regions. Sustainability, 11(5), 1227.
Economidou, M., Atanasiu, B., Despret, C., Maio, J., Nolte, I., Rapf, O., Laustsen, J., Ruyssevelt, P., Staniaszek, D., Strong, D., et al. (2011). Europe’s buildings under the microscope: A country-by-country review of the energy performance of buildings.
FOEN. (2022). Environment Switzerland 2022 (Tech. Rep.). Swiss Federal Council.
FOEN, F. O. (2023). Earthquakes: Information for specialists. Retrieved December 4, 2024, from https://www.bafu.admin.ch/bafu/en/home/topics/natural-hazards/topic-earthquakes.html
Galimshina, A., Moustapha, M., Hollberg, A., Lasvaux, S., Sudret, B., & Habert, G. (2023). Recommendations for robust renovation strategies of Swiss residential buildings.
Galimshina, A., Moustapha, M., Hollberg, A., Padey, P., Lasvaux, S., Sudret, B., & Habert, G. (2020). Statistical method to identify robust building renovation choices for environmental and economic performance. Building and Environment, 183, 107143.
Galimshina, A., Moustapha, M., Hollberg, A., Padey, P., Lasvaux, S., Sudret, B., & Habert, G. (2021). What is the optimal robust environmental and cost-effective solution for building renovation? Not the usual one. Energy and Buildings, 251, 111329.
Galimshina, A., Moustapha, M., Hollberg, A., Padey, P., Lasvaux, S., Sudret, B., & Habert, G. (2022). Bio-based materials as a robust solution for building renovation: A case study. Applied Energy, 316, 119102.
Göswein, V., Pittau, F., Silvestre, J. D., Freire, F., & Habert, G. (2020). Dynamic life cycle assessment of straw-based renovation: A case study from a Portuguese neighbourhood. IOP Conference Series: Earth and Environmental Science, 588(4), 042054.
Lee, H., Calvin, K., Dasgupta, D., Krinner, G., Mukherji, A., Thorne, P., Trisos, C., Romero, J., Aldunce, P., Barret, K., et al. (2023). IPCC, 2023: Climate change 2023: Synthesis report, summary for policymakers. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee, and J. Romero (eds.)]. IPCC, Geneva, Switzerland.
Margani, G., Evola, G., Tardo, C., & Marino, E. M. (2020). Energy, seismic, and architectural renovation of RC framed buildings with prefabricated timber panels. Sustainability, 12(12), 4845.
Marini, A., Passoni, C., Belleri, A., Feroldi, F., Preti, M., Metelli, G., Riva, P., Giuriani, E., & Plizzari, G. (2022). Combining seismic retrofit with energy refurbishment for the sustainable renovation of RC buildings: A proof of concept. European Journal of Environmental and Civil Engineering, 26(7), 2475–2495.
Masih, A. (2018). An enhanced seismic activity observed due to climate change: Preliminary results from Alaska. IOP Conference Series: Earth and Environmental Science, 167, 012018.
Pittau, F., Krause, F., Lumia, G., & Habert, G. (2018). Fast-growing bio-based materials as an opportunity for storing carbon in exterior walls. Building and Environment, 129, 117–129.
Pittau, F., Lumia, G., Heeren, N., Iannaccone, G., & Habert, G. (2019). Retrofit as a carbon sink: The carbon storage potentials of the EU housing stock. Journal of Cleaner Production, 214, 365–376.
Pohoryles, D., Maduta, C., Bournas, D., & Kouris, L. (2020). Energy performance of existing residential buildings in Europe: A novel approach combining energy with seismic retrofitting. Energy and Buildings, 223, 110024.
Priore, Y. D., Habert, G., & Jusselme, T. (2023). Exploring the gap between carbon-budget-compatible buildings and existing solutions–A Swiss case study. Energy and Buildings, 278, 112598.
Scuderi, G. (2019). Retrofit of residential buildings in Europe. Designs, 3(1), 8.
Silva, A., Castro, J. M., & Monteiro, R. (2020). A rational approach to the conversion of FEMA P-58 seismic repair costs to Europe. Earthquake Spectra, 36(3), 1607–1618.
WGBC. (2019). Bringing embodied carbon upfront: Coordinated action for the building and construction sector to tackle embodied carbon.