Roof Coatings Research Articles

Thermal Performance of Becool-Roof Coating in Reducing Heat Gain on Fisherman’s Settlement of Gorontalo City

Abstract Tanjung Kramat in Gorontalo, Indonesia is a village fostered by the department of Architecture, Universitas Negeri Gorontalo. The village is home to around two hundred families whose majority job is fishing. The people suffer from the uncomfortable condition of tropical coastal environment due to the high air temperature, humidity, and wind speed. Not to mention people in Gorontalo prefer to cover their upper structure using metal zincalume roof since they are more affordable. The highly thermal conductivity roof accounts for excessive heat gain to the house. Through a CSR program by Becool, the villagers received Cool Roof Coating to reduce heating and mitigate global warming. Before and after painting measurements of roof surface temperatures, radiant temperatures, and ground air temperatures are conducted. After the application of the coating, the analysis shows a positive result as the roof surface temperature is reduced by about 20ºC, followed by an improvement in ground air temperature by an average of 0.8ºC. The cool roof coating has succeeded in improving the neighborhood of Tanjung Kramat village.

Assessing Energy Savings: A Comparative Study of Reflective Roof Coatings in Four US Climate Zones

Assessing Energy Savings: A Comparative Study of Reflective Roof Coatings in Four US Climate Zones

The effects of cool roofs on health, environmental, and economic outcomes in rural Africa: study protocol for a community-based cluster randomized controlled trial

BackgroundHigh ambient air temperatures in Africa pose significant health and behavioral challenges in populations with limited access to cooling adaptations. The built environment can exacerbate heat exposure, making passive home cooling adaptations a potential method for protecting occupants against indoor heat exposure.MethodsWe are conducting a 2-year community-based stratified cluster randomized controlled trial (cRCT) implementing sunlight-reflecting roof coatings, known as “cool roofs,” as a climate change adaptation intervention for passive indoor home cooling. Our primary research objective is to investigate the effects of cool roofs on health, indoor climate, economic, and behavioral outcomes in rural Burkina Faso. This cRCT is nested in the Nouna Health and Demographic Surveillance System (HDSS), a population-based dynamic cohort study of all people living in a geographically contiguous area covering 59 villages, 14305 households and 28610 individuals. We recruited 1200 participants, one woman and one man, each in 600 households in 25 villages in the Nouna HDSS. We stratified our sample by (i) village and (ii) two prevalent roof types in this area of Burkina Faso: mud brick and tin. We randomized the same number of people (12) and homes (6) in each stratum 1:1 to receiving vs. not receiving the cool roof. We are collecting outcome data on one primary endpoint - heart rate, (a measure of heat stress) and 22 secondary outcomes encompassing indoor climate parameters, blood pressure, body temperature, heat-related outcomes, blood glucose, sleep, cognition, mental health, health facility utilization, economic and productivity outcomes, mosquito count, life satisfaction, gender-based violence, and food consumption. We followed all participants for 2 years, conducting monthly home visits to collect objective and subjective outcomes. Approximately 12% of participants (n = 152) used smartwatches to continuously measure endpoints including heart rate, sleep and activity.DiscussionOur study demonstrates the potential of large-scale cRCTs to evaluate novel climate change adaptation interventions and provide evidence supporting investments in heat resilience in sub-Saharan Africa. By conducting this research, we will contribute to better policies and interventions to help climate-vulnerable populations ward off the detrimental effects of extreme indoor heat on health.Trial registrationGerman Clinical Trials Register (DRKS) DRKS00023207. Registered on April 19, 2021.

Factors to Consider in Developing Conceptual Scopes of Repair for Common Low-Slope Roofing Assemblies

Forensic engineers are commonly asked to develop conceptual scopes of repair as part of their work. Many factors impact these recommendations, including building codes, construction feasibility, manufacturer assessment, and installation requirements. In addition, the conditions present on and within the existing roof surfaces can limit the repairability of a commercial roof assembly such that removal and replacement of the entire roof section is the appropriate or only feasible repair option. This paper will focus on common limitations to be considered when developing a conceptual scope of repair for common commercial roof systems, including single-ply membranes, built-up roofing, metal panel roofing, spray polyurethane foam roofing, and the application/maintenance of roof coatings. It will also discuss an assessment methodology that can assist in developing a broader understanding of the condition of the roof surfaces.

Green hydrogen production using bifacial solar photovoltaics integrated with high-albedo roof coating & micro-inverter

Green hydrogen is a key factor for the decarbonization of the energy sector and to foster the clean energy transition but has the highest cost when compared to grey and blue hydrogen. This is due to the high cost of the generation of energy from renewable sources and the efficiency of the water electrolyzer. Future innovative energy technologies are needed to boost the power production from solar PV systems, reduce the cost of renewable electricity and enhance hydrogen production from electrolyzers. The main objective of this study is to investigate green production enhancement using a bifacial solar PV system integrated with cool roof technology (high-albedo roof coatings). The best-reflecting surface needs to be determined to maximize the power output from the bifacial solar PV system and the green hydrogen production. The originality and novelty of this study lie in the fact that it integrates innovative technologies such as bifacial solar PV and building cool roofs in order to boost the power generation output and green hydrogen production. The experimental set-up is composed of bifacial solar PV, a building roof with high solar reflective material, a microinverter, an electrolyzer, a metal hydride hydrogen tank, and an integrated data acquisition system. The results show that the green, grey, and white reflecting surfaces exhibit the albedo of 16.76 %, 17.87 % and 24.45 % respectively resulting in 17.26 %, 19.72 % and 28.47 % enhancement in power production by bPV as compared to reference mPV. Further, whiteboard, patterned wallpaper and cool roof paint coating are assessed and have shown 24.09 %, 29.66 % and 30.27 % rear side irradiance on the bPV as compared to the front side, resulting in 28.10 %, 31.30 % and 33.02 % increase in energy generation. The results conclude that cool roof paint outperforms the others and enhances the power output of bPV by 33.02 % resulting in 30.26 g of H2 production as compared to 22.75 g by mPV under the same conditions. Hence, cool roof paint improves the energy production of bPV solar resulting in high production of H2.

An Analysis of the Influence of Cool Roof Thermal Parameters on Building Energy Consumption Based on Orthogonal Design

An analytical hierarchy model of the impact of solar reflectance, thermal emittance, heat transfer coefficient, and heat storage coefficient on building energy consumption was established through the implementation of orthogonal design experiments. The EnergyPlus software (v9.0.1) was utilized to simulate building energy consumption across diverse climatic regions in China, providing essential benchmarks for the orthogonal design. The results of the range analysis consistently indicate that, barring regions characterized by extremely cold climates, solar reflectance emerges as the predominant factor exerting an influence on building energy consumption. As geographical latitude increases, the impact of the heat transfer coefficient becomes progressively larger, while the weight of thermal reflectance concurrently diminishes. Drawing upon the principles rooted in the gradient refractive rate theory and the concept of atmospheric window radiation, a range of high-reflectance and high-emittance cool roof coatings in various colors were meticulously developed. A spectrophotometer was employed to precisely quantify their reflectance properties, and simulations were subsequently conducted to scrutinize their energy-saving characteristics. The results demonstrate that the cool roof coatings that were developed using the methodology described in this paper exhibit substantial enhancements in reflectance, with increases of 0.24, 0.25, 0.37, and 0.35 for the yellow, red, blue, and green cool roofing materials, respectively, in comparison to conventional colored coatings. Under typical summer conditions, these enhancements translate to significant reductions in roof temperatures, ranging from 9.4 °C to 14.0 °C. Moreover, the simulations exploring the cooling loads for the roofs of differing colors consistently revealed remarkable energy savings. These savings were quantified to be 4.1%, 3.9%, 5.5%, and 5.4%, respectively, when compared to conventional coatings of the corresponding colors. These findings offer valuable insights into strategies for optimizing the energy efficiency of buildings through the application of high-reflectance cool roofing materials.

Algae biofilm induced surface erosion of acrylic coatings

A major factor influencing failures of water-based elastomeric roof coatings is extended exposure to ponding water, biofilm development, attachment, and damage. Development of improved coatings is slow due to outdoor exposure tests that can take years. The goal of this work is to develop accelerated test methods and to understand the mechanism of biofilm-induced damage of coatings. Two model acrylic coatings on TPO substrates were exposed to lab-controlled accelerated growth of biofilm (algae) in ponding water to learn about coating damage before and after subsequent wet-dry cycles. Three distinct damage features in sequence were observed: (1) pit formation on the coating surfaces, (2) the biofilm mud-cracking induced coating surface damage upon drying, and (3) erosion (surface cracks) of coating in the mud-cracked region over the wet-dry cycles. Drying of adequately bonded biofilm to the coating and the thickness of the biofilm are the critical factors that govern the erosion on the coating surfaces. The effect of the wet-dry cycle time period was studied with respect to the surface erosion of the coatings. The mechanisms of biofilm-induced erosion during wet-dry cycling are postulated based on the mechanics and experimental observations. A new accelerated testing methodology for evaluating long-term roof coating performance is proposed.

A Systematic Analysis of Phase Change Material and Optically Advanced Roof Coatings Integration for Athenian Climatic Conditions

Energy retrofit solutions that concern a building’s roof structure play a significant role in the enhancement of a building’s thermal behaviour. This study investigates the integration of phase change materials (PCMs) with cool coatings (CCs) or thermochromic coatings (TCCs), namely, a PCM roof, a PCM-CC roof, and a PCM-TCC roof, as alternative and novel tactics for the simultaneous control of solar heat transfer and solar heat reflection. An energy simulation analysis with the DesignBuilder tool is conducted for a one-story residence and the climatic conditions of Athens. The simulation results indicate that, compared to the existing concrete roof construction, the PCM roof, PCM-CC, and PCM-TCC roof systems demonstrate energy savings that reach up to 13.55%, 16.04%, and 21.70%, respectively. The systematic analysis reveals that the increase in PCM’s thickness leads to an increase in the total electricity savings of the buildings, but in the case of PCM-CC and PCM-TCC roof systems, they merely effect the cooling thermal loads. The mean phase transition temperature that favours the cumulative electricity savings is 28 °C in the case of PCM and PCM-TCC roof systems and 35 °C in the case of PCM-CC roof systems. The methodology of this study allows the design of efficient, integrated roof systems with advanced thermal and optical properties as energy retrofit solutions for Mediterranean climatic conditions.

Study of the influence of local materials insulation on cooling loads of a house made of breeze block or laterite in a dry tropical climate

In this paper, we study the influence of local materials for insulating roof and fiber-reinforced mortar coatings on cooling loads of a home in dry tropical climate. The wall of the housing is made of cinderblock or laterite and the insulating material of a roof panel is made with lime (24%), cement (6%), water (50%) of vegetable fibers hibiscus sabdariffa (16%), tree widespread in Burkina Faso and sugar cane bagasse (4%). This panel roof insulation and the fiber-reinforced mortar were characterized at the Laboratory of Physics and Chemistry of the environment by the hot plate method. The building is modeled in TRNSYS using climate data from the city of Ouagadougou. The results obtained show that in the warmer months of the year, that is to say in March and April, the relative differences between heat gains configurations the configurations “breeze block-coating mortar and roof not insulated” and ‘laterite- fiber-reinforced mortar coating and insulated roof’ vary between 15.6 % and 16.8 %. Configuration ‘laterite- fiber-reinforced mortar coating and insulated roof allows a reduction of annual heat gains of 15.5% compared to the configuration ‘breeze block-coating mortar and roof not insulated’.

The Impact of Roof Coating and Solar PV System in the Tropical Region of Ghana

Adding PV module to roof has impacts on building`s electricity energy consumption. The aim of this paper is to assess the energy consumption performance of buildings by integrating solar Photovoltaic (PV) system into buildings with roof coating. An experiment was conducted to verify the efficient outcome of PV module using a building from the Anaji area of Takoradi in the Western region of Ghana. A framework energy model was proposed to analyse the integrated contribution of coating and PV performance using PVSOL. The temperature of the coated roof surfaces underneath the PV panels were significantly lower than that of the exposed roof in the daytime. The system integrated energy efficiency for flat and tilted overhead PV roofs are 63.35 % and 62.73 %, respectively. Using the mean absolute percentage error (MAPE) performance criterion, the monthly energy savings for coated roofs with solar PV is 28.86 kW or GH¢ 340.21; while the monthly energy savings for coated roofs without PV is 25.91 kW or GH¢ 303.00. Overall, the proposed integrated coated roof with PV outperforms the coated roof without PV. Validating the model, the mean relative errors (MRE) were all below 10%, while the accuracy of Power-Added Efficiency (PAE) were all beyond 95%. Thus, the proposed integrated roof coating and solar PV model for optimizing energy consumption is reliable.

Exploring energy-efficient building solutions in hot regions: A study on bio-phase change materials and cool roof coatings

Creating low-energy buildings in arid, hot desert climates like Kuwait poses significant challenges. This research examines the potential of Bio-PCMs and cool roof coatings as energy-saving methods in three hot climate locations, using both experimental and computational approaches. Two identical portable cabins were meticulously constructed, and their thermal properties were analysed under two different cooling conditions. These cabins offer a unique testing ground for various energy-saving techniques, as their thermal similarity has been experimentally confirmed. A six-zone model was developed in TRNSYS software to study Bio-PCM integrated walls. The findings for the desert climate of Kuwait and subtropical climate of Rockhampton, Australia, demonstrated the best performance with autoclaved aerated concrete block walls, achieving energy performance indices of 761.7 and 496.3 kWh/m2/year, respectively. Bio-PCMs integration in three positions within walls and roof were examined, which were yielded energy savings of 22%, 23%, and 53% in Kuwait, Australia, and India, respectively, while experimental results on two cool roof methods, cool roof paint and aluminium foil roof, indicated that energy savings proved to be negligible. Incorporating insulation materials via sandwich panels in buildings can substantially enhance energy efficiency in Kuwait and Australia, with observed reductions of 35.7% and 43.8% compared to autoclaved aerated concrete blocks from simulation results. However, in tropical climate of Kodaikanal, India, energy consumption were increased dramatically by 126.2% when sandwich panels were used. This study offers valuable insights into optimal wall materials and energy-saving strategies, such as cool roof methods, insulation and Bio-PCM, for use in various hot climates.

Fabrication and Characterization of Carbon Nanofibers Coated Expandable Thermoplastic Microspheres-Based Polymer Composites

Background: Thermoplastic expandable microspheres (TEMs) are spherical particles that consist of a polymer shell encapsulating a low boiling point liquid hydrocarbon that acts as the blowing agent. When TEMs are heated at 80-190 °C, the polymer shell softens, and the hydrocarbon gasifies, causing the microspheres to expand, leading to an increase in volume and decrease in density. TEMs are used in food packaging, elastomeric cool roof coatings, shoe soles, fiber and paper board, and various applications in the automotive industry. It is noted that TEMs are known by their brand name ‘Expancel’, which is also used to refer TEMs in this paper. Objective: The objective of this work was to develop and characterize forms prepared from TEMs with/without carbon nanofibers (CNFs) coatings to study the effect of CNFs on structural, thermal, and mechanical properties. Method: Sonochemical method was used to coat TEMs with various weight percentages (1, 2, and 3%) of CNF. Neat foam (without CNF) and composite foams (TEMs coated with various wt.% of CNF) were prepared by compression molding the TEMs and TEMs-CNF composites powders. Thermal and mechanical properties of the neat and composite foams were investigated. Result: The mechanical properties of the composite foam were notably improved, which is exhibited by a 54 % increase in flexural modulus and a 6% decrease in failure strain with the TEMs-(2 wt.% CNF) composite foam as compared to the neat foam. Improvement in thermal properties of composite foam was demonstrated by a 38% increase in thermal stability at 800ºC with the TEMs-( 1 wt.% CNF) composite foam as compared to the neat foam. However, no change in the glass transition of TEMs was observed with the CNF coating. SEM-based analysis revealed that CNFs were well dispersed throughout the volume of the TEMs matrix, forming a strong interface. Conclusions: Straightforward sonochemical method successfully triggered efficient coating of TEMs with CNFs, resulting in a strong adhesion interface. The mechanical properties of composite foams increased up to 2% of CNFs coating and then decreased with the higher coating, presumably due to interwoven bundles and aggregation of CNFs, which might have acted as critical flaws to initiate and propagate cracking. Thermal properties of foams increased with the CNFs coating while no change in glass transition temperature was observed due to coating.

Analysis of the Dome-Chamber’s Openness in Persian Historical Mosques

The dome, one of the most stable forms of roof coatings, has passed many of its evolution stages in the dome-chambers of Iranian mosques. From the Seljuk era, when the first dome-chambers were seen, to today, the extent of the openness of the dome-chamber space to the adjacent space—shabestans and the porches—has changed a lot. This research seeks to answer the questions of why and how openness has happened and what factors have influenced their intensity. Since there may be different answers to these questions at different periods, the physical properties of the domes were studied in terms of measurable variables, both in the general context and in each period. For this purpose, 51 dome-chamber mosques were selected from Seljuk to Qajar periods, with variation in physical characteristics. The research method is a combination of content analysis method, comparative study and logical reasoning based on the descriptive and correlational statistics. As a result, it has been shown that structural constraints related to the extent and magnitude of the dome-chamber, are considered the main reasons for deciding how much and how to open the dome-chamber’s walls in different periods and that as the ratio of the span to the wall thickness increases, the openness of the walls decreases to the same extent. Also, the architecture of seljuk and safavid mosques are more similar than the other periods, possibly due to the common religious characteristics that affected them both.

Novel superhydrophobic NIR reflective coatings based on Montmorillonite/SiO2 composites for Energy-saving building

In recent years, cool building materials have received increasing attentions due to their superior energy-saving efficiencies. In this work, novel self-cleaning cool coatings based on fluorocarbon resin-montmorillonite (MMT)/SiO2 composites were prepared for energy-saving buildings. The intercalation modification of MMT improved the dispersion stability of MMT in organic solvent. Surface modification of MMT and SiO2 particles by fluoroalkyl silane (FAS) produced hydrophobic particles. Fluorocarbon resin was used as a binder. With the assistance of the micro/nano structure of montmorillonite/SiO2 composites and low surface energy of FAS and fluorocarbon resin, superhydrophobic state of the MMT/SiO2 composite coatings can be achieved. The maximum contact angle of the MMT/SiO2 composite coatings was as high as 163.5°. The superhydrophobic composite coatings exhibited superior self-cleaning property and good mechanical durability. Furthermore, the NIR solar reflectance of the superhydrophobic montmorillonite/SiO2 composite coatings ranged from 0.77 to 0.85. The composite coatings reduced the heat box’s inside temperature of by 5.9℃. Therefore, the integration of high NIR reflectance property and superior self-cleaning property makes montmorillonite/SiO2 composite coatings good candidates as self-cleaning cool roof coatings for energy-saving buildings.

Modeling the effect of roof coatings materials on the building thermal temperature variations based on an artificial intelligence

This paper presents the benefits of applying the artificial neural networks technique to model the building indoor temperature variations caused by implementing roof coatings. Four of the most common roof coating used in Mexican constructions were considered. The study evaluated test cells at outdoors and instrumented them to measure the indoor temperature variation. The environmental parameters solar radiation, wind speed, ambient temperature, and relative humidity were also monitored. The results showed the viability of modeling the thermal behavior generated by the roof coatings with an accuracy greater than 90%. It implies the ability to predict internal temperatures based on the physical properties of the material and environmental variables, being a feasible tool in the search for thermal comfort for buildings in the region. In addition, the results of the sensitivity analysis identified to what extent to improve the optical properties of the material impact on the heat transferred to the interior.

Temperature-adaptive radiative coating for all-season household thermal regulation.

The sky is a natural heat sink that has been extensively used for passive radiative cooling of households. A lot of focus has been on maximizing the radiative cooling power of roof coating in the hot daytime using static, cooling-optimized material properties. However, the resultant overcooling in cold night or winter times exacerbates the heating cost, especially in climates where heating dominates energy consumption. We approached thermal regulation from an all-season perspective by developing a mechanically flexible coating that adapts its thermal emittance to different ambient temperatures. The fabricated temperature-adaptive radiative coating (TARC) optimally absorbs the solar energy and automatically switches thermal emittance from 0.20 for ambient temperatures lower than 15°C to 0.90 for temperatures above 30°C, driven by a photonically amplified metal-insulator transition. Simulations show that this system outperforms existing roof coatings for energy saving in most climates, especially those with substantial seasonal variations.

Impact of light-colored paint materials on discomfort in a building for hot-dry climate

India is a tropical country with diverse climates, and thermal adaption plays a significant role in sustaining thermal comfort in non-conditioned buildings. Indoor air temperature is taken as the main parameter for thermal comfort in buildings, which is very high in western India and creates uncomfortable for occupant. Thermal comfort is a primary need inside the buildings from a human health perspective. Roof structure and the color of the exterior surface affect the thermal comfort of the buildings in a hot-dry climate. Roof contributes maximum heat gain towards the outdoor temperature wave amplitude and time lag in non-conditioned buildings during summer. Three commercially available reflective paints or coatings were selected and used in the simulation to assess the performance of a non-conditioned building. In this paper, we present the evaluation ofthe discomfort index (DI) and Tropical Summer Index (TSI) for the summer season (April and May).The comfort hours achieved using cool roof coatings were 12–17 hours more than the base case or conventional roof used in a hot-dry climate. The tropical summer index (TSI) was found adequate within its comfort range (27.5 °C) for roofs with surface coatings than a base case roof slab.

Laboratory scale characterization of cool roof paints: Comparison among different artificial radiation sources

A series of cool coatings realized with three pigments displaying YIn0.9Mn0.1O3-ZnO stoichiometry and different colors (Ochre, Cyan Blue, and Deep Blue) was deposited on AA5005 aluminum substrate. Coatings were investigated by vis/NIR spectrophotometry. The color was evaluated according to CIE-1976L*a*b* method. The innovative approach of this study aims to compare the effectiveness of three different radiation sources (incandescent infrared emitting lamp, tungsten halogen one, and xenon arc one) to properly assess the thermal reflective performance of cool roof coatings. These thermal evaluations were compared with the performances obtained by natural sunlight exposition. In this way was individuated the best sun simulator in terms of temperature and spectral emission, matching NIR reflectance response of the investigated cool roof materials. Considering these two last points the best solar simulator results the xenon arc lamp. Using this radiation source the Deep Blue coating is the best performing coating, as cool surface coating; the other two coatings show promising results.

Effect of Aging on Solar Reflectance of White Cool Roof Coatings: Natural Weathering and the Influence on Building Energy Needs for Different Climate Conditions in Brazil

The use of cool materials on the building envelope is one of the most cost-effective ways to increase indoor thermal comfort conditions in hot climates and decrease the cooling energy needs. Despite the benefit of reducing cooling loads, researches have demonstrated that aging of roof coatings changes the initial solar reflectance (SR), which influences the long term building thermal and energy performance. Thus, this work presents preliminary natural weathering tests performed on samples of nine white coatings exposed to natural weathering for one year in the city of Sao Carlos, Brazil. Solar reflectances were measured with a spectrophotometer before and after exposure, every 3 months, for identifying the effect of aging along the time. The findings showed changes of 13% to 23% on SR after one year of natural weathering, with higher decrease on SR for rougher surfaces. The cleaning process restored from 90% to 100% of the original SR, which means maintenance can be an effective solution to restore the initial SR. Simulations indicated that roofs with higher solar reflectance increase indoor thermal comfort conditions and decrease the cooling energy need for buildings in hot climates, but the aging of white coatings increased the cooling energy needs along the time

Development of a new spectral selectivity-based passive radiative roof cooling model and its application in hot and humid region

Radiative sky cooling has attracted worldwide attention due to its passive cooling potential with zero energy input. Daytime cooling materials with outstanding spectral properties are developing rapidly. Using these new cooling materials as roof coatings can become one of the most prominent radiative cooling methods integrated with buildings. Current existing models and numerical tools are not able to incorporate the spectral selectivity of radiative cooling materials and local precipitable water vapor, thus failing to accurately predict roof thermal performance. To this end, the paper newly develops a spectral selectivity-based passive radiative roof cooling model to integrate full spectral properties of emerging cooling materials and consider precipitable water vapor-induced atmospheric radiation for precise evaluation of roof cooling performance. A field experiment was carried out to validate the developed model. The mean bias errors (MBEs) of the model in the prediction of rooftop temperatures were found less than 4.6%, verifying the sufficient accuracy of the new model in characterizing roof temperature variations. After validation, the developed model was used to investigate the potential benefits of radiative cooling as a rooftop strategy in the hot and humid region of Hong Kong. The whole year on-site weather data were collected as the model input. Compared to the baseline coating, the reductions in monthly cumulative roof thermal transfer values by applying a porous polymer cooling coating are 18.5–22.3, 33.7–40.5 and 2.9–3.5 kWh/m2 for residential concrete-based, industrial galvanized steel-based, and standard-compliant commercial multilayered roofs, respectively. For the above three roofs, the radiative cooling coating is able to save the annual roof-induced cooling electricity of 54.7–76.6, 97.4–136.4, and 8.8–12.2 kWh/m2, corresponding to the cooling cost saving of 71.8–100.5, 127.8–179.0, 11.5–16.0 HK$/(m2·yr), respectively. The new spectral selectivity-based radiative roof cooling model can be widely employed to accurately evaluate the utilization of daytime radiative coolers as a rooftop strategy in improving building thermal and energy performance.