Potential Retrofit Research Articles

Data-driven optimization reveals the impact of Urban Heat Island effect on the retrofit potential of building envelopes

The urban heat island (UHI) effect significantly impacts building energy consumption, but its effect on energy retrofit potential remains unclear. Here, we propose a data-driven surrogate optimization framework to assess the energy-saving potential of improving building envelope thermal performance in 101 public buildings in Shenzhen. The framework integrates batch building energy modeling, ensemble learning surrogate model training, and multi-objective optimization. The potential changes in building loads resulting from different parameter combinations are defined as energy-saving potential. We use the Urban Weather Generator to adjust typical meteorological year data and account for UHI effects in energy modeling. The results indicate that neglecting the UHI effect in Shenzhen overestimates the potential for building energy retrofitting by approximately 25.2 % (office buildings: -8.96 %, commercial buildings: 60.7 %). Among the nine thermal retrofitting parameters, the heat transfer coefficient of windows contributes the most to the energy-saving potential. Considering the UHI effect or not leads to significant differences in retrofitting strategies and optimal retrofitting parameter configurations. These findings underscore the importance of considering the UHI effect and interactions between buildings in energy retrofit modeling and decision-making processes to formulate precise retrofit strategies and schemes.

How green can it be? A methodology for calculating green roof retrofit potential in Valencia

Cities are accountable for more than 70% of global CO2 emissions and consume around 65% of the world's energy. In the pathway towards urban decarbonisation, nature-based solutions rise as a promising opportunity. They improve a city's resilience, stabilise temperatures and capture CO2, both mitigating climate change effects and adapting to them. This paper presents a novel methodology to assess the potential effects of green roof retrofit in urban areas, selecting suitable buildings for greening and estimating their decarbonising capacity. The proposed method combines the use of Geographic Information Systems (GIS) and artificial vision algorithms to select the roofs. Once selected, direct carbon sequestration and energetic savings are estimated based on empirical results. This methodology is successfully applied to the L'Illa Perduda neighbourhood of Valencia (Spain) as a case study. The GIS analysis shows that about 50% of the roofs' surface could be greened, directly absorbing around 350 tCO2yr−1 and reducing the energetic emissions of the neighbourhood in about 100 tCO2yr−1 by improving the insulating envelope of the buildings. The artificial vision computation selected 38% of the surface of the neighbourhood residential buildings.

Exploring seismic fragility and strengthening of masonry built heritage in Lisbon (Portugal) via the Applied Element Method

Although mainland Portugal has been spared from large magnitude earthquakes in recent years, it faces a threat due to the presence of several active fault systems. In such a framework, Portuguese pre-code masonry construction is believed to be the most vulnerable in the existing building stock. Given the lack of information on earthquake damage to this stock, the use of detailed numerical models is a viable strategy to comprehend its seismic behavior. This paper provides an updated fragility characterization of Lisbon pre-code masonry buildings based on their seismic assessment through the Applied Element Method. To limit the computational time, a promising pushover strategy, known as Incremental Ground Acceleration, was adopted. After the characterization of the current fragility, two retrofit layouts based on piers strengthening were modeled and assessed for the building stock whose seismic capacity does not meet expected demand. The aim of the paper is to derive updated fragility curves for the Lisbon region to support risk analysis incorporating the latest hazard studies and to offer insights into potential retrofit interventions.

Energy transition in the retail sector: Revealing decision-making behaviours for energy efficiency retrofits of Dutch shopping centres

Shopping centres hold significant energy retrofit potential in the retail sector. However, their complex multi-stakeholder governance structure complicates decision-making for Energy Efficiency Retrofits (EER). Although literature identifies some barriers linked to EER, they are often scattered and not identified within a process perspective that considers their contextual complexities. This study addressed this gap by examining stakeholders’ behaviours, barriers, and relations during EER decision-making processes, to detect stakeholders’ needs to catalyse the energy transition. Qualitative research was conducted on three representative Dutch shopping centres case studies. The cross-case analysis uncovered the decision-making process for EER and new barriers attributed to this building typology. Amongst other, detected barriers can be attributed to limitations with governmental and internal regulations, lifecycle conflicts, proposed interventions being out of scope, and existing technical challenges. The study also revealed causal relationships among stakeholders, showcasing varying interpretations of barriers and highlighting the roles of owners, property managers, and public authorities in overcoming them. Furthermore, the findings indicate the key role that different contextual variables play in the EER decision-making process, such as ownership type, governance structure, and leasing structure. This study offers insights and recommendations for shopping centre owners, property managers, and policymakers, to support them in navigating the energy transition of the retail building stock. Key recommendations include decentralizing decision-making, optimizing governance structure, streamlining sustainability advisors, and acknowledging the collaborative roles of property managers and policymakers in providing effective and holistic solutions.

Sustainable energy solutions: Well retrofit analysis and emission reduction for a net-zero future in the Intermountain West, United States of America

To achieve net-zero emissions by 2050, we need economic means of sequestering carbon dioxide (CO2) and reducing greenhouse gas emissions (GHG). We analyze the sequestration potential of the Intermountain West (I-West) region, US, as a primary energy transition hub through analysis of wellbore retrofit potential and emission reduction in both fugitive gas abatement and flare gas. We selected the I-West region due to its abundant energy sources and oil and gas production legacy. Preliminary analysis hints that well retrofits can breathe new life into a well at a fraction of the cost of a new drill. With millions of potential candidates in the US, even a modest fraction (1% or less) suitable for retrofit could accelerate the shift to large-scale CO2 sequestration. Fugitive gas, the unintentional release of wellbore gases such as methane, is a significant emissions source. Through conservative analysis, it is estimated that wellhead leakage alone may account for 5 million tonnes of carbon dioxide equivalent (CO2e) emissions. We conclude by assessing the CO2 emissions from flaring, which is the burning of associated gas during well operations, conservative analysis indicates flaring contributes another 2 million tonnes of CO2 emissions to the region. We find that with targeted retrofit and better controls on emissions sources, the I-West region can make a significant impact in the nation's push to become net-zero. This study outlines economic feasibility and actionable items to achieve the critical reductions in emissions and increases in sequestration necessary to attain net zero.

Assessing the Energy Performance and Retrofit Potential of the 1980–1990s’ Residential Building Stock in China’s Jiangsu Province: A Simulation-Based Study

The building operation sector in China represents 22% of the national energy consumption and 22% of the carbon emission, of which urban residential buildings accounted for 24% in 2019. Such figures for the housing sector are projected to increase sharply in the near future, while China aims to peak CO2 emissions by 2030 and reach neutrality before 2060. To reduce the impacts of the urban housing sector and address the energy use and waste generated by large-scale demolition and reconstruction, the central government started promoting the energy retrofit of urban residential buildings, raising such policies to the national strategic level. Jiangsu Province is one of the most urbanised, with a rapid growth in the energy consumption of residential buildings. The Multi-Danyuan and Single-Danyuan Apartment built in 1980–1999 are the most representative residential types in its urban areas. While still adequate functionally, they were designed and built to low energy standards and show significant potential for energy retrofit. Nonetheless, their current performance and energy-saving potential are under-researched, while more detailed and reliable data would be critical to support retrofit design and policy making. This study investigates and characterises the typical use and energy performance of the two building types. Additionally, seven measures and six retrofit scenarios were identified based on the optimal energy reductions and regulations from selected countries. The simulations indicate that, without intervention, the energy consumption of the typical urban residential buildings can reach 122 kWh/m2 under the typical high-energy user scenario. By selecting a set of effective energy-saving measures, the operational energy use for heating and cooling can be reduced by up to 52.4%. Current local standards prove cost-efficient, although less effective in reducing energy use compared to international best practices, indicating potential improvements to the contribution of building retrofit towards achieving the national carbon reduction goals.

Post-Fracture Stiffness and Residual Capacity Assessment of Film-Retrofitted Monolithic Glass Elements by Frequency Change

The primary goal of safety films for glass in buildings is to retrofit existing monolithic elements and prevent, in the post-fracture stage, any fall-out of shards. Their added value is that—as far as the fragments are kept bonded—a cracked film-glass element can ensure a minimum residual mechanical and load-bearing capacity, which is strictly related to the shards interlocking and debond. To prevent critical issues, such a mechanical characterization is both important and uncertain, and requires specific methodologies. In this regard, a dynamic investigation is carried out on fractured film-bonded glass samples, to assess their post-fracture stiffness trends and its sensitivity to repeated vibrations. The adopted laboratory layout is chosen to assess the effects of random vibrations (220 repetitions) on a total of 12 cracked specimens in a cantilever setup (with 0.5–5 m/s2 the range of randomly imposed acceleration peaks). By monitoring the cracked vibration frequency, the film efficiency and corresponding residual bending stiffness of cracked glass samples are quantified as a function of damage severity, with a focus on fragments interlock. Quantitative experimental estimates are comparatively analyzed and validated with the support of finite element (FE) numerical models and analytical calculations. As shown—at least at the small-scale level—a progressive post-fracture stiffness reduction takes place under repeated random vibrations, and this implicitly affects the residual load-bearing capacity of glass members. Most importantly, for the tested configurations, it is shown that the cracked vibration frequency is minimally affected by crack geometry, and follows a rather linear decrease with the number of imposed random impacts (up to an average of ≈20 for each sample), thus confirming the retrofit potential and efficiency in providing some mechanical capacity through fragments interlock.

Assessing multifunctional retrofit potential of urban roof areas and evaluating the power and carbon benefits under efficient retrofit scenarios

Green roof installations and photovoltaic (PV) systems are widely employed roof retrofits that aid cities in mitigating climate change impacts, while avoiding the need for increased land utilization. By integrating PV systems with vegetation on urban roofs, a photovoltaic-green (PV-Green) system can be achieved for multifunctional use of the roof space, thereby simultaneously achieving PV and greening benefits. However, current research solely based on one retrofit type cannot meet the requirement for assessing the multifunctional retrofit potential of urban roofs. In this study, an assessment method is proposed to identify and quantify the multiple retrofit potential of urban roofs by integrating roof attributes (slope, orientation, and area), roof type (gable or flat), solar attributes (radiation and irradiation duration), and biogeochemical simulation. Moreover, three roof retrofit scenarios, Scenario 1 (S1): maximization of PV-Green roofs, Scenario 2 (S2): maximization of PV economic benefits, and Scenario 3 (S3): maximization of public subjective well-being through roof greening, were designed to allocate the use of urban roof spaces and evaluate their respective potential power and carbon benefits at the city scale. Using Shanghai's downtown as an example, the results showed that 85,722 roofs (or 7310.86 ha) were available for multifunctional use. S1 revealed that applying PV-Green roofs can increase the additional green biomass by 0.74 × 107 kg C/yr compared to only installing PV roofs. Moreover, S1 produced the highest power output of 2.31 × 1010 kWh/yr to meet 15.4% of Shanghai's electricity demand. S2 identified 609 flat roofs and 70,527 gable roofs that were uneconomical for PV system installation. This indicated that the solar radiation received by most gable roofs was insufficient to cover the installation cost. S3 offered a biomass production of 1.48 × 107 kg C/yr and increased carbon stocks in Shanghai by 0.87%. This assessment method provides urban planners and policymakers with an analytical tool to optimize the use of urban roof spaces, thereby enhancing urban livability and sustainability.

Tapping the potential of anammox upgrading in full-scale wastewater treatment plants through biofilm-enhanced anammox and denitrification

Implementing the Anammox process at a large scale remains a significant challenge. However, this study presents a potential approach for upgrading full-scale wastewater treatment plants (WWTPs) to incorporate the Anammox process in treating ammonium-rich wastewater. The research focuses on a WWTP at a duck breeding farm that utilizes an anaerobic/microaerobic/anoxic/oxic (A/M/A/O) process. With 83% removal of total nitrogen, the contribution of anammox and denitrification nitrogen removal in the entire process was 52% and 31%, respectively. The study tracks the changes in water quality and analyzes the potential of simultaneous Anammox-denitrification processes to mitigate nitrate accumulation. Porous carriers were introduced into the primary anaerobic tank (Anaerobic T1) and the primary microaerobic tank (Microaerobic T1) and were harvested on the 90th day. The results revealed that the specific Anammox activity (SAA) of the microaerobic biofilm reached 252.06 mg N/g VSS·d, which was 6.0 times and 3.7 times higher than that of suspended sludge and anaerobic biofilm, respectively. The microaerobic biofilm demonstrated the capacity for simultaneous Anammox-denitrification, with anammox and denitrification rates of 65.35 and 36.3 nmol N/g·h, respectively. These rates were significantly higher than those observed in the anaerobic biofilm and suspended sludge. Furthermore, the main partial denitrification bacteria identified were Ignavibacterales UTCHB1 (57.75%) and Trichococcus (5.12%), which contributed nitrite to Candidatus Brocadia (1.54%). The findings highlight the importance of creating a suitable microenvironment using porous carriers, which facilitates the Anammox pathway for nitrogen removal in biofilms. This approach presents a potential retrofitting and upgrading strategy for existing WWTPs.

National building stock model for evaluating the impact of different retrofit measures

In this study, a methodology was developed to evaluate different retrofit strategies, which allows an estimation of the current and future thermal space heating demand of the approximately 1.8 million residential buildings in Switzerland. The approach is based on a building stock dynamics model that considers new buildings, replacement buildings, demolitions, as well as past and current rates of energy-related retrofits. Different potential retrofit strategies are applied to evaluate their impact on reducing space heating demand. The results show the effectiveness of the distinct retrofit strategies in reaching the target reduction and emphasize the differences in the resulting annual retrofit rates. The simulated specific retrofit rates can serve as a basis for developing building retrofit measures at the national level, as well as for informing the next generation of regulations.

Flexure Strengthening and Analysis Using CFRP Composite and Reactive Powder Concrete

There are many cases of carbon fiber-reinforced polymer (CFRP) and reactive powder concrete (RPC) in structural repair and reinforcement, but there are not many related theoretical and experimental discussions. Therefore, the purpose of this research is to focus on the experiment and theoretical calculation of the flexural strengthening of concrete beam specimens. The study was primarily separated into two parts. In the first part, the laboratory tests of flexure strengthening by using CFRP and two reactive powder concretes (RPC1 and RPC2) are used to evaluate the effect of strengthening concrete beams. Secondly, the test value of the maximum flexure failure load of the strengthening specimen using RPC or CFRP and its theoretical value calculated by the transform section method or the ultimate strength method are discussed and compared with their reinforced effect. The test results show that the RPC and CFRP display excellent repair and retrofit potential. The RPC reinforcement material with a thickness of 2 cm and a steel fiber content of 1.0% is approximately equal to the reinforcement effect of three layers of CFRP. In particular, the RPC reinforcement effect is good, and the bonding interface is not damaged. The transform section method could be used to analyze and calculate the maximum flexure failure load of the RPC strengthening concrete beam. The transform section method and ultimate strength method cannot accurately analyze the maximum flexure failure load of the CFRP-strengthening concrete beam.

Optimal ship lifetime fuel and power system selection under uncertainty

Ship designers face increasing pressure to comply with global emission reduction ambitions. Alternative fuels, potentially derived from bio-feedstock or renewable electricity, provide promising solutions to this problem. The main challenge is to identify a suitable ship power system, given not only uncertain emission requirements but also uncertain fuel and carbon emission prices. We develop a two-stage stochastic optimization model that explicitly considers uncertain fuel and carbon emission prices, as well as potential retrofits along the lifetime. The bi-objective setup of the model shows how the choice of optimal power system changes with reduced emission levels. Methanol and LNG configurations appear to be relatively robust initial choices due to their ability to run on fuel derived from different feedstocks, andtheir better retrofittability towards ammonia or hydrogen. From a policy perspective, our model provides insight into the effect ofthe different types ofcarbon pricing mechanismson a shipowner’s decisions.

Performance-based seismic resilience and sustainability assessment of coastal RC bridges in aggressive marine environments

Corrosion-induced deterioration of material properties can noticeably affect the seismic performance of coastal reinforced concrete (RC) bridges in aggressive marine environments, causing significant adverse economic and environmental consequences post extreme events. This study systematically investigates the time-dependent seismic performance, resilience, and sustainability of coastal RC bridges. For that purpose, a three-dimensional (3D) nonlinear finite element (FE) framework is developed and combined with the formulation of performance-based earthquake engineering (PBEE) and an economic input-output life cycle assessment (LCA) approach. Seismic resilience and robustness of the coastal RC bridges are subsequently evaluated in terms of the post-earthquake repair cost, repair time, and carbon footprint quantified by CO2. Within this framework, additional analyses are conducted to explore possible retrofit measures, including the use of fiber-reinforced polymer (FRP) reinforcement on the sustainability and resilience of the retrofitted RC bridges. For the presented scenario, it is shown that wrapping bridge columns with FRP composites can effectively increase the moment capacity, thus improving resilience and sustainability by reducing as much as 650 Mg of CO2 for this specific bridge. Overall, the derived insights highlight the need for sustainability, resilience, and potential retrofit analysis of coastal RC bridges in seismically active regions affected by corrosion-induced deterioration.

Exergy and performance analysis of low GWP and Non-flammable HFO based refrigerant mixtures as alternatives to R134a

R1234yf and R1234ze(E) can be potential retrofits for the conventional refrigerants used in domestic refrigerator provided their flammability is controlled. In this study, the inerting effect of the dilutants R125, R134a, R227ea and R245fa on R1234yf and R1234ze(E) based ternary mixtures is studied theoretically. R152a, R161 and RE170 are used as the secondary refrigerants with R1234yf and R1234ze(E) based ternary mixtures. Minimum inerting concentration (most important parameter that decides the flammability of the mixture) is estimated with thermal balance method (TBM) and modified thermal balance method (MTBM) for the selected mixtures. The calculated MIC values are compared with 86 experimental data points (both binary and ternary) available in the literature. It is calculated that TBM and MTBM predicted the minimum inerting concentration values (for a majority of the mixtures) within ±30% and ±8% respectively when compared with the experimental data. The COP ratios of the non-flammable mixtures (that are proposed with MTBM) are estimated and is found to be maximum at a volumetric cooling capacity ratio close to 0.8. It is also calculated that the exergy efficiency varied between 0.54 to 0.64 for the low GWP mixtures (M1 to M5) proposed in this study.

A Survey of Environmental Performance Enhancement Strategies and Building Data Capturing Techniques in the Nigerian Context

The need to improve the performance of Nigeria’s office buildings is due to, energy challenges, increasing population, changing user needs, and climate change. With the expansion of several Nigerian cities, existing buildings constitute a significant portion of the building stock, and improving their environmental performance could be more cost-effective than reconstruction. The use of simulation packages to assess alternative retrofitting enhancement scenarios is a straightforward approach. However, in Nigeria it is often challenging to get appropriate information to facilitate this type of evaluation; many buildings were not built to their original specifications, and when available, the records are often in a poor state due to deterioration. Studies that aimed at enhancing a building’s performance hardly stated the acquisition of the required building information. This paper investigates current practices and future possibilities of improvement measures and data capturing of existing buildings using a questionnaire survey of 133 building professionals in Benin City. The inter-relationship between energy efficiency, the environment, and building design with a high potential for meaningful retrofit to mitigate energy inefficiencies is known but not fully utilized. The collected thought on current practices signifies the need for developing a more economical and reliable methodology for data capturing and evaluation.

Experimental Investigation on Aging and Energy Savings Evaluation of High Solar Reflective Index (SRI) Paints: A Case Study on Residential Households in the GCC Region

Energy-efficient retrofitting of building envelopes is necessary to reduce global carbon emissions and to reach net-zero goals. Cooling energy demand-dominated countries in the GCC region require simple and effective strategies to reduce building sector energy loads. One such approach is using high solar reflective index (SRI) paints to retrofit building roofs and walls. However, the hot and desert conditions of the region pose a barrier to maintaining consistent radiative properties throughout their life cycle. To this extent, research is limited in the region. The novelty of this work is to qualitatively assess the aging characteristics of high SRI or cool paints and estimate the energy savings for their application in residential buildings. The work encompasses comprehensive lab, pilot, and real-scale experimental studies combined with theoretical modeling for dynamic evaluation. Dynamic simulations enabled to determine the time-dependent aging effect on the energy savings performance of the building retrofitted with cool roof and wall paints. A case study on a townhouse in UAE showed annual energy savings of 34% considering cool roofs, walls, and window films. Aging studies showed SRI reduction of 36% and 25%, respectively, for cool roofs and walls during the first 3 years. The corresponding energy-saving reductions ranged from 31 to 44% for the white roof to dark wall colors. Using the initial values of SRI in energy models overestimates saving by 10% per year. Considering the aging effects, this work provides insights into cool paint retrofit potential on energy, economic savings, and CO2 reductions for four major cities in the GCC region.

Approximating optimal building retrofit solutions for large-scale retrofit analysis

Coordinated large scale building retrofit is one of the most effective approaches not only to reduce the environmental footprint of existing buildings but also to assure that climate goals can be met. Existing bottom-up retrofit approaches become infeasible or lack in terms of accuracy and/or computational cost especially when the scale of application increases in size. Hence, the aim of this paper is to propose and develop a bottom-up approach for large-scale building retrofit with the use of a scalable building-level surrogate retrofit model. To ensure scalability and generalization to large areas, we use artificial neural networks. The developed approach consists of a set of artificial neural networks trained on building archetypes, aiming to predict near-optimal building retrofit solutions for all residential buildings in Switzerland. This is achieved with a small set of inputs, and within a short run time. In order to validate the developed approach, we compare it with a conventional mixed building simulation and optimization approach. The surrogate model computes near-optimal building retrofit solutions, with an average coefficient of determination of 0.91 and an average f1 score of 0.89. To illustrate the advantages of this model, we perform a large-scale retrofit analysis of a case study in Geneva municipality. Such a surrogate model is capable of providing insights into the overall retrofit potential of large areas and thus shall support reaching energy emission reduction targets of existing residential buildings.

Building energy retrofit simulation for exploring decarbonization pathways in a community-scale food-energy-water-waste nexus

• A food-energy-water-waste nexus analysis can aid in low carbon city design • System dynamic modeling analysis synthesizes low carbon city initiative. • Scenario planning helps identify decarbonization pathways for prioritization. The retrofit of existing buildings at a community scale can provide a huge opportunity to reduce the community's energy consumption and subsequent greenhouse gas (GHG) emissions in support of the United Nations agenda for net-zero emissions and decarbonization. This study demonstrates a community-scale food-energy-water-waste nexus through 6 scenarios (A1–A6) by highlighting decarbonization pathways with system dynamics modeling. Several potential retrofit alternatives are proposed for analyzing building energy consumption, energy requirements for rooftop or greenhouse crop production, and potential energy and water savings from renewable energy harvesting. Such a nexus analysis is designed to integrate (1) building energy consumption, (2) waste management and water consumption, and (3) GHG emissions based on life-cycle assessment to prioritize scenarios. The incorporation of solar photovoltaic (PV) systems (i.e., rooftop, parking lot, parking garage, and floating solar PV) sustains approximately 72% of net energy demand (scenario A3), while the integration of all solar, wind, and anaerobic digestion alternatives provides around 41% of net energy demand (scenario A6). It is vital to emphasize decarbonization pathways through the use of renewable energy by 2030 in scenario A5 (i.e., solar and wind energy) and A6, both of which avoid energy consumption from the utility grid and result in 250% total carbon emissions offset.

Pathways to improving the school stock of England towards net zero

A disaggregated (school-level) analysis of the retrofit potential of primary and secondary schools of England is presented, using data from a highly detailed database of the energy use and characteristics of the school stock. The overall carbon emissions reduction potential for the stock is explored under different packages of retrofit measures, as well as how the rollout of those measures between the present and 2050 might shape the pathways towards net zero. Even with a fixed set of assumptions about what measures are implemented and at what rate, it is shown that decisions about the deployment process can greatly affect the annual and cumulative emissions of the overall stock over the coming decades. Under certain scenarios, decisions about the criteria used to define the school retrofit order can result in a doubling of cumulative emissions by 2050, or impact whether the interim 2035 target is met. <em><strong>Policy relevance</strong></em> The performance of England’s primary and secondary schools, and how it might improve in the context of long-term carbon emissions reduction targets, is shown. The paper quantifies how decisions about the deployment of retrofits determine the pathways that the stock will take towards net zero. The analysis shows considerable emissions reductions are feasible, through a mix of building envelope improvements, conversion to electric heating, rooftop photovoltaics and aided by projected improvements to the grid. However, the results show that—even with a high deployment rate (650 schools/year to retrofit all schools by 2050)—the approach taken to deploying those retrofits (<em>i.e.</em> the policies and guidance that dictate which schools are prioritised for improvement) will determine the long-term performance of the overall stock and whether or not interim emissions targets can be met.

Can We Retrofit Suburban Arterials?

Problem, research strategy, and findings The multilane arterial roadway is a central feature of post–World War II (WWII) suburbs that challenges efforts to create more transit-oriented regions. Retrofitting suburbs is an important planning goal, but research examining the urban form of arterials and their potential for transformation has been scarce. We analyzed four suburban corridors in the Toronto (Canada) region developed during different periods of suburbanization. We found that the walkability of corridors declined as modernist planning ideas were more fully implemented, and then walkability increased as new urbanist ideas began to influence planning in the 1990s. Over time, however, the retrofit potential declined across all corridors studied, with patterns of lots and development becoming ever more static. Understanding these patterns is important to developing successful strategies for retrofitting suburban arterials. Takeaway for practice Arterial roadway corridors present potential to bring transit-oriented, walkable urban places near large areas of automobile-dependent suburbs and should be a primary focus for retrofitting research and practice. We present here a set of metrics that rely on readily available data, are not complex to carry out, and produce mapping and visualization that is legible and allows comparison across corridors. We suggest that local governments should be routinely studying and evaluating the potential for retrofit and intensification of all such corridors within their jurisdiction. Planners should seek to develop approaches to managing future corridor development to permit greater adaptability in response to future economic, transportation, and climate changes and vulnerabilities.