A Comprehensive Review of Life Cycle Assessment (LCA) Studies in Roofing Industry: Current Trends and Future Directions

Highlights

Main findings:

• There is significant variability in LCA methods and impact categories in roofing studies.
• Only a few studies have examined roofing components at the urban scale.

Implications of the main finding:

• Standardized LCA methods are needed for consistent assessments in the roofing industry.
• More urban-scale LCA studies are needed to better understand the environmental impact of roofing materials.

Abstract

The building sector is crucial in keeping the environment healthy, mainly because of its energy and material usage. Roofs are one of the most important components to consider, as they not only shield the building from the elements but also have a big impact on the environment. The paper provides a state-of-the-art review of the life cycle assessment (LCA) application in the roofing industry. The review examines three main focus areas: (1) LCA of different roofing materials, (2) LCA of roofing systems, and (3) whole-building LCA. Key takeaways from the literature review demonstrate that there is significant variability in LCA methods and impact categories assessed across roofing studies. Only a few studies have explored the complete urban scale in LCA assessments of roofing components. Future research can include utilizing the potential of LCA at urban scales, which can offer a full understanding of the environmental impacts associated with roofing materials in urban settings.

1. Introduction

The roofing industry plays a pivotal role in the built environment, providing protection, thermal insulation, and aesthetic appeal to structures worldwide. As sustainability becomes increasingly imperative across all sectors, the construction industry is under heightened scrutiny to minimize environmental impacts while maintaining performance and durability [1,2]. Life cycle assessment (LCA) emerges as a powerful tool to evaluate the holistic environmental footprint of roofing materials, systems, and entire buildings, facilitating informed decision-making and fostering sustainable practices within the industry. Product Category Rules (PCRs) play a crucial role in ensuring consistency and transparency when conducting LCAs for roofing products and systems. PCRs are a set of specific rules, requirements, and guidelines for developing Environmental Product Declarations (EPDs), which communicate the environmental performance of a product or system based on LCA results. Several PCRs have been developed in the roofing industry to standardize the LCA methodology and reporting for various roofing materials and systems. For instance, the Metal Construction Association (MCA) has published a PCR for metal roof and wall cladding products, which provides guidelines for conducting LCAs and developing EPDs for these products. Similarly, the European Resilient Flooring Manufacturers’ Institute (ERFMI) has developed a PCR for roofing and waterproofing membranes, including EPDM (Ethylene Propylene Diene Monomer) and other single-ply roofing materials. These PCRs typically outline the system boundaries, functional units, data requirements, impact categories, and other methodological aspects that should be followed when conducting LCAs for the respective roofing products or systems. Adhering to these PCRs ensures consistency in the LCA approach, enabling fair comparisons between different roofing options and facilitating the development of reliable EPDs. Core rules for environmental product declarations of construction products and services”) provide overarching guidelines for developing PCRs and EPDs in the construction sector, including roofing products and systems. Aligning these standards further enhances the credibility and comparability of LCA studies and EPDs in the roofing industry.

2. Materials and Methods

This comprehensive review aims to synthesize the existing body of LCA studies within the roofing sector, delineating current trends and identifying potential future directions. The review is structured into three primary sections, each focusing on distinct aspects of the roofing life cycle: material production, roofing system installation and operation, and the comprehensive evaluation of entire buildings (Figure 1). By categorizing LCA studies into these sections, the aim is to provide a structured overview that elucidates the environmental impacts associated with different stages of a roofing product’s life cycle.

The first section presents a detailed examination of LCA studies about roofing materials. Roofing materials encompass a diverse range of options, including but not limited to asphalt shingles, metal roofing, clay and concrete tiles, and green roofing systems [3]. Each material possesses unique characteristics that influence its environmental performance across various life cycle stages, from raw material extraction and manufacturing to end-of-life disposal or recycling. By critically analyzing LCA studies within this context, the aim is to elucidate the comparative environmental profiles of different roofing materials and identify opportunities for optimization and innovation. The second section delves into LCA reviews focusing on roofing systems. Unlike individual roofing materials, roofing systems encompass a combination of materials, components, and installation methods tailored to specific climatic, structural, and aesthetic requirements. Consequently, assessing the environmental impacts of roofing systems entails a more complex analysis, considering factors such as system design, installation practices, maintenance requirements, and end-of-life considerations. Through a systematic review of LCA studies in this domain, the goal is to discuss the environmental implications of different roofing system configurations and highlight opportunities for enhancing sustainability throughout their life cycles. The final section expands the scope to encompass whole-building LCA studies within the context of roofing. Buildings represent intricate assemblies of various components, with the roof playing a crucial role in the overall environmental performance of the structure. Whole-building LCAs offer a holistic perspective by considering the interconnectedness of building elements and their cumulative environmental impacts over the entire life cycle. By synthesizing findings from whole-building LCA studies, one can broaden the environmental implications of roofing choices within the context of sustainable building design and construction.

Overall, this review paper provides a comprehensive synthesis of LCA studies in the roofing industry, offering valuable insights into current trends, methodological approaches, and areas for future research. By synthesizing the key insights and trends from the existing literature, the review highlights areas where further research is needed to address gaps and improve the understanding of the environmental impacts associated with roofing systems. This comprehensive analysis provides valuable guidance to support the development of more sustainable roofing solutions.

3. Results

3.1. LCA Studies Examining Individual Roofing Materials

Life cycle assessment (LCA) studies are vital for understanding how different building materials impact the environment. This section looks closely at the environmental analysis of different roofing materials using LCA studies. Each roofing material has its features depending on its manufacturing, life, and disposal.

Bhyan et al. [4] discussed the LCA of lightweight and sustainable construction materials, focusing on the environmental impacts of different building materials used in a residential case study in Jaipur, India. The study used a two-story residential building with an 800 m² built-up area as a case study. They evaluated three material typologies: traditional stone, conventional burnt red clay bricks, and modern precast concrete components. The LCA was conducted using One Click LCA software, considering the cradle-to-gate stages of material production, transportation, construction, maintenance, replacement, and end-of-life. The results showed that the precast concrete construction had the highest embodied carbon emissions of 428 kg CO₂-eq./m³. Stone construction had emissions of 225 kg CO₂-eq./m³, and brick construction had the lowest emissions of 137 kg CO₂-eq./m³. The authors emphasized the importance of considering LCA in material selection and building design to promote sustainability in the construction industry. It suggests using materials with lower environmental impacts, such as bricks, over precast concrete components. Another LCA study [5] investigated the primary energy demand, global warming potential (GWP), and water demand of various building materials. The study found that ceramic tiles, fiber cement roofs, and conventional insulation materials like expanded polystyrene (EPS) and polyurethane foam had the highest environmental impacts. The authors proposed more sustainable options, which included quarry tiles over ceramic for paving, natural insulation like rock wool and cork, and wood products that have negative GWP due to CO₂ absorption during growth. It was noted that the cement production was energy-intensive, so using concrete with high cement content increased impacts compared to materials mixed with gravel. Vaz and Sheffield [6] conducted a preliminary LCA to estimate the greenhouse gas (GHG) emissions associated with the manufacturing, utilization, and disposal of atactic polypropylene (APP)-modified asphalt membrane roofs. The study used LCA software GaBi 4.4 to model the product’s life cycle stages based on data from the manufacturer. The results showed that the manufacturing stage accounted for 69% of total GHG emissions, with fuel-based raw materials like asphalt and polypropylene responsible for 70–80% of CO₂ emissions. The disposal stage accounted for significant methane emissions (84%) due to the landfill disposal of products. The overall GHG emissions were estimated at 75.2 kg CO₂-eq., with carbon dioxide (63.4%) and methane (36%) as the major contributors. The authors concluded that compared to other roofing membranes, the APP-modified asphalt membrane had lower emissions.

Several studies were conducted to quantify the environmental impact of cooling roof material and roof tiles. Sravani et al. [7] conducted a comparative life cycle assessment (LCA) study to evaluate the environmental impact of different passive cooling roof materials for a residential building in India. The study used the One Click LCA tool integrated with a BIM model of a two-story residential building in Tirupati, India. The results showed that for the existing building without any insulation (Case 1), the total carbon dioxide equivalent (CO₂-eq.) emissions were 433,579 kg. By replacing the conventional red clay bricks with autoclaved aerated concrete (AAC) blocks for wall insulation (Case 2), the CO₂-eq. emissions decreased by 6.06% to 407,532 kg. The study concluded that wall and roof insulation can reduce CO₂ emissions by 1–6%, as well as other environmental impacts like acidification, eutrophication, and ozone depletion potentials, compared to an uninsulated building. On a similar note, another study [8] evaluated the environmental sustainability of clay roofing tiles by comparing two manufacturing practices—semi-conventional and modern—using the LCA approach. The authors considered a cradle-to-gate study, excluding use and end-of-life phases. Life cycle inventory data were collected through site visits, measurements, and industry contacts. The authors used ReCiPe and IPCC methods for impact assessment in SimaPro software. The results showed that the firing process contributed the highest global warming potential (GWP) in both practices, with 19.2 kg CO₂-eq. for modern (due to LPG usage) and 1.84 kg CO₂-eq. for semi-conventional (due to biomass usage). The study concluded that the modern manufacturing practice has higher environmental impacts compared to semi-conventional, particularly in terms of global warming, human health, and resource depletion impacts, primarily due to the use of LPG as fuel, and highlighted the need for technological improvements and sustainable energy solutions to reduce these impacts. The study by Binh et al. [9] evaluated the environmental impacts of different roofing materials: sheet metal, concrete tiles, and clay tiles, using an LCA approach in Western Australia. It was noted that the sheet metal had the highest carbon footprint of 9.85 t CO₂-eq., with 96% from raw material acquisition. Concrete tiles were found to have a footprint of 9.33 t CO₂-eq., with 51% from raw materials and 43% from manufacturing. Clay tiles had the lowest footprint of 4.39 t CO₂-eq., with 76% from manufacturing (natural gas combustion) and 10% each from raw materials and transportation. The authors found that using the recycling approach, sheet metal and concrete tiles’ footprints were reduced by 73% and 45%, respectively, while clay tiles had a negligible reduction, as waste was crushed for other applications.

Kayan and Ashraf [10] investigated the embodied carbon emissions associated with repairing Singgora roof tiles on heritage buildings in Malaysia. The research integrated embodied carbon and LCA approaches to evaluate the environmental impact of maintenance interventions on three case studies of heritage buildings with Singgora roof tiles. The authors quantified the embodied carbon emissions within the cradle-to-site boundary, including material processing, manufacturing, and transportation emissions for the repair materials, and expressed functional units as embodied carbon per m² (kg CO₂-eq./kg/m²) for repairing 1 m² of roof surface area with Singgora tiles. The results showed that the emissions for Case Study 1, Case Study 2, and Case Study 3 were 1.775668.8 kg CO₂-eq. for 100 repairs, 172714.6 kg CO₂-eq. for 200 repairs, and 1376954.4 kg CO₂-eq. for 50 repairs, respectively. Hafner and Schäfer [11] conducted a comparative LCA study of different timber and mineral building designs for residential buildings in Germany and Austria. The study evaluated the global warming potential (GWP) expressed over a 50-year lifespan for various timber (cross-laminated timber, timber frame, prefabricated) and mineral (brick, sand-lime brick, concrete) building designs. The results showed that for single/two-family houses, timber buildings had 9–48% lower GWP than functionally equivalent mineral counterparts over the full life cycle. An eight-story timber building with a reinforced concrete staircase core was found to have only 9% lower GWP than its mineral counterpart, representing the lower bound of the analyzed multi-story cases. Souza et al. [12] conducted a comparative life cycle assessment of ceramic versus concrete roof tiles in the Brazilian context. The study compared the environmental impacts across the full life cycle, from raw material extraction to manufacturing, transportation, use, and end-of-life disposal. The results showed that ceramic tiles had lower impacts on climate change, resource depletion, and water withdrawal compared to concrete tiles. It was noted that the key contributors to the impacts of ceramic tiles were transportation (climate change, resource depletion) and wood combustion (human health, ecosystem quality). For concrete tiles, major impact sources were cement production (climate change) and transportation (human health, ecosystem quality, resource depletion). The study highlighted the opportunities to reduce impacts, such as using renewable energy for concrete production and improved filtration for ceramic tile manufacturing emissions.

Other studies [13,14] used the LCA methodology to assess the environmental cost of a bitumen anti-root barrier on a green roof at the University of Calabria in Southern Italy. Maiolo et al. [13] aimed to evaluate the sustainability of using bitumen membranes as an anti-root layer before and after the operational phase of the green roof. The impact assessment using the ReCiPe Endpoint and Impact 2002+ methods showed that the damage category with the greatest weight was Resources, linked to raw material extraction processes and the use of non-clean energy sources. The authors identified CO₂ as the most important emission, contrasting with the primary function of green roofs to reduce climate change impacts in urban areas. The study by Ma et al. [14] demonstrated an LCA analysis of a 60-story high-rise office building with a reinforced concrete and steel composite structure in Chicago. The results showed the total embodied carbon was 5.7 × 10⁷ kg CO₂-eq. The product stage dominated 81% of the total embodied carbon, with concrete production contributing 55% and steel production 24% during this stage. It was further noted that for other impact categories like acidification and eutrophication potentials, concrete contributed around 60% during the product stage. The study concluded concrete is the primary driver of environmental impacts, especially embodied carbon, in high-rise building structures. The life cycle carbon emissions of recycled fine aggregate (RFA) concrete were evaluated by considering the effects of RFA replacement ratio, compressive strength, and transportation distance [15]. The authors found that increasing the RFA ratio reduces the compressive strength but also lowers the emissions from material production. The authors developed an analytical model relating RFA ratio, compressive strength, and emissions, showing that the detrimental effect of RFA on strength reduction outweighed the emissions benefit. Sensitivity analysis found the water–cement ratio was the most influential factor on emissions, followed by the RFA ratio and transportation distance.

Another study [16] investigated the environmental impacts of materials used in green roof layers, focusing on the production of polymers like low-density polyethylene (LDPE) and polypropylene (PP) used for root barriers, drainage, and water retention layers. It was illustrated that producing 1 kg of non-recycled LDPE releases 2 kg of CO₂, while 1 kg of non-recycled PP releases 1.7 kg of CO₂. The authors suggested that using recycled polymers can reduce these emissions, but they still have environmental impacts from additives, acids, and other substances used in the recycling process. It was recommended to consider the full life cycle impacts of green roof materials, not just their operational benefits, to ensure they are truly environmentally sustainable solutions. Rincón et al. [17] investigated the environmental performance of using recycled rubber crumbs from tires as the drainage layer in extensive green roofs compared to conventional pozzolana gravel drainage layers and conventional flat roofs. The authors found that in the production phase, the green roof with recycled rubber had a 20% higher environmental impact than a non-insulated conventional roof, mainly due to the dismantling process of tires to obtain the rubber crumbs. However, in the operational phase, the green roof with recycled rubber provided 13% energy savings for cooling and 6.7% savings for heating compared to the green roof with pozzolana gravel. Compared to a non-insulated conventional roof, the recycled rubber green roof had 19.5% cooling energy savings and 5.9% heating energy savings. The recycled rubber green roof had similar annual energy use to an insulated conventional roof but provided 14.8% cooling energy savings. Overall, using recycled rubber instead of pozzolana reduced the operational phase environmental impact by 7.8% while giving a second life to waste material. The authors recommended recycled rubber as an environmentally beneficial drainage layer for extensive green roofs. An LCA study was conducted by Bozorg Chenani et al. [18] to evaluate the environmental impacts associated with different layers and substrate compositions in extensive green roof systems. The study analyzed two substrate compositions: (1) a mixture of crushed brick (80%), expanded clay (10%), and compost (10%); and (2) a mixture of pumice (70%), compost (15%), and sand (15%). The production phase results showed that substrate 1 had significantly higher impacts than substrate 2 across most categories, with the use of expanded clay being the main contributor to impacts like marine ecotoxicity for substrate 1. For substrate 2, compost production was the primary impact source. Further, excluding expanded clay from substrate 1 (substrate 3) and considering zero impacts from compost (substrate 4) resulted in the lowest impacts for six out of nine categories compared to other green roof layers. The results demonstrated that during the usage phase, green roofs were estimated to provide benefits like reducing acidification based on a previous Chicago study, though results were sensitive to this assumption for a different climate. A study by Takano et al. [19] focused on comparing different LCA databases for building materials and components. The results showed that there were significant differences in the greenhouse gas (GHG) emission values calculated using the various databases, with percentage relative differences ranging from −25% to 33% compared to the reference EcoInvent database. The authors found that the databases with more comprehensive, transparent data and clear statements on underlying assumptions/methods tend to improve the comparability of LCA results. The authors demonstrated the importance of data availability, representativeness, and transparency in LCA databases to ensure reliable environmental assessments, especially for complex products like buildings composed of many materials.

A summary of LCA studies investigating the environmental impact of individual roofing materials is summarized in

Table 1. Review of LCA studies examining individual roofing materials.

Year	Location	Focus	Key Findings	Ref.
2023	India	Lightweight Construction Materials	The study compared traditional stone, burnt clay bricks, and precast concrete, with bricks having the lowest emissions.	[4]
2011	Spain	Different Bricks and Tiles	The study highlighted the high environmental impacts of ceramic tiles, fiber cement roofs, and insulation materials.	[5]
2014	United States	Atactic Polypropylene (APP)-Modified Asphalt Membrane Roofs	The manufacturing stage contributed most to GHG emissions, and APP-modified asphalt had lower emissions.	[6]
2022	India	Passive Cooling Roof Materials	Insulation reduces CO2 emissions, and different roofing materials have varying impacts.	[7]
2020	Sri Lanka	Clay Roofing Tiles	The study highlighted the environmental sustainability of clay roofing tiles compared to other practices.	[8]
2019	Western Australia	Roofing Materials	Concrete tiles had the highest carbon footprint, while clay tiles had the lowest footprint.	[9]
2023	Malaysia	Singgora Roof Tiles	Embodied carbon emissions for repairing Singgora tiles on heritage buildings were quantified.	[10]
2017	Germany, Austria	Timber and Mineral Building Designs	Timber buildings have lower GWP than mineral counterparts, especially in single/two-family houses.	[11]
2015	Brazil	Roof Tiles	Ceramic tiles have lower impacts on climate change, resource depletion, and water withdrawal compared to concrete tiles.	[12]
2018	Southern Italy	Bitumen Anti-Root Barriers	Bitumen membranes have high environmental costs, mainly due to CO2 emissions, contrasting with green roof benefits.	[13]
2024	United States	High-rise Building Structures	Concrete contributes significantly to embodied carbon in high-rise buildings, especially during the product stage.	[14]
2022	China	Recycled Fine Aggregate Concrete	Increasing the recycled fine aggregate ratio reduces emissions, but it affects compressive strength.	[15]
2012	Canada	Green Roof Layers	The production of polymers for green roof layers has significant CO2 emissions.	[16]
2014	Spain	Recycled Rubber Crumbs	Recycled rubber as a drainage layer reduces the operational phase’s environmental impact compared to conventional materials.	[17]
2015	Finland	Extensive Green Roof Systems	The selection of substrate components is crucial for minimizing environmental impacts in extensive green roof systems.	[18]
2014	Finland	Different Roofing Materials	Significant differences exist in GHG emissions across databases, highlighting the importance of data transparency.	[19]

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3.2. LCA of Roofing Systems

While the previous section reviewed LCA studies focusing primarily on assessing the environmental impacts of individual roofing material options, it is also important to evaluate complete roofing system assemblies. An LCA of full roofing system assemblies can capture the combined impacts from all these elements over the complete life cycle. A roofing system LCA can also shed light on areas for design optimization, such as minimizing excess materials or enhancing end-of-life reuse. This section demonstrates the findings from LCA literature that have evaluated various roofing systems and assemblies across different building types and climates.

Several studies performed the LCA studied on different green roof systems [20,21,22]. Scolaro and Ghisi [20] investigated the life cycle environmental impacts of different green roof layers and materials. The study compared alternative green roof compositions, i.e., varying the materials used for the root barrier (polyethylene and PVC), a protection layer (light and heavy non-woven polypropylene), drainage layer (recycled and virgin high-impact polystyrene), water retention layer (recycled textile fibers and rock wool), and lightweight soil components (perlite, peat moss, peats, coal ash, and zeolite). The authors found that the polyethylene root barrier had lower impacts than PVC in all impact categories. Further, the recycled high-impact polystyrene drainage layer had lower impacts than virgin material, and recycled textile fibers for the water retention layer had lower impacts than rock wool in all categories. Among lightweight soil components, zeolite had the highest impact (49–90%) in almost all impact categories, while coal ash accounted for over 60% of eutrophication and non-renewable energy use. The authors recommended using recycled materials and a simple green roof design to reduce environmental impacts. Peri et al. [21] conducted an LCA study of an extensive green roof system installed on a research building in Sicily, Italy. The study focused on evaluating the environmental impacts associated with the growing medium (substrate) used in the green roof. The substrate analyzed in the study was a mixture of inert volcanic materials (lapillus, pumice, and zeolithe) and organic materials (peat, compost, and NPK slow-release organic fertilizers) with a thickness of 15 cm. The production phase was modeled using primary data from suppliers and the Ecoinvent database. The end-of-life phase assumes the disposal of inert materials in a landfill. The LCA results showed the production of fertilizer used for maintenance was the most significant contributor to eutrophication and terrestrial ecotoxicity impacts, while disposal of the growing medium and bitumen in landfills during end-of-life had the highest impacts on human toxicity and marine aquatic ecotoxicity. The study highlighted the importance of obtaining accurate data on substrate composition and maintenance practices to conduct a comprehensive LCA of green roof systems. Brachet et al. [22] investigated the impact assessment of different roof systems, i.e., conventional roofs, extensive green roofs, semi-intensive green roofs, and intensive green roofs. The study used a functional unit of 1 m² of roof area with a 40-year lifespan and conducted a cradle-to-grave LCA. The authors modeled roof components and processes based on data from literature and databases like EcoInvent and AGRIBALYSE. They used ReCiPe 2016 and Impact World+ methods to assess ecosystem damage and calculated indicators like global warming, acidification, eutrophication, ecotoxicity, land use, and water consumption The results showed that for all roof systems, “ex situ” biodiversity (affected outside construction site) was 10 times more impacted than “in situ” biodiversity. Conventional roofs had the highest total biodiversity loss, and the intensive green roof had the lowest impact (37% lower than conventional roofs per ReCiPe).

Berardi et al. [23] investigated the state-of-the-art analysis of the environmental benefits of green roofs. The authors reported that green roofs reduce roof surface temperature by 12–30 °C and ambient air temperature by 0.5–3 °C compared to conventional roofs. Further, increasing soil depth by 10 cm resulted in an increase in thermal resistance by 0.4 m²K/W for dry clay soil. It was noted that green roofs reduce daily surface temperature variation from 45 °C for conventional roofs to only 6 °C. In summer, green roofs can decrease heat gain by 60% compared to conventional roofs. The results demonstrated that increasing vegetation density improved the energy performance benefits of green roofs across different cities. Kosareo and Ries [24] conducted a comparative life cycle assessment of green roofs versus conventional roofs. It was depicted that for the extensive green roof, the energy use reduction from improved insulation was the critical factor in determining its lower environmental impact compared to a conventional roof. The authors found that the extensive green roof had an expected lifespan of 45 years, which is three times the 15-year conventional roof lifespan. It was noted that over the full life cycle, the extensive green roof had the lowest environmental impacts across impact categories like acidification, eutrophication, and global warming potential when accounting for reduced operational energy use. Vacek et al. [25] conducted an LCA study to evaluate the environmental impacts of four semi-intensive green roof (SIGR) assembly configurations, with a focus on the growing medium layer. The study analyzed (1) a common assembly with intensive substrate and dimple drainage, (2) assembly 1 with added extruded polystyrene (XPS) insulation, (3) assembly 1 with mineral wool replacing substrate, and (4) mineral wool panels as near-total substrate replacement with thin extensive substrate layer. The results revealed that assembly 2 with XPS insulation had the highest impacts in categories like global warming potential due to the energy-intensive XPS production. Assembly 4, with mineral wool panels, had the highest impacts on acidification and eutrophication potentials, attributed to the mineral wool production process. The authors emphasized the importance of carefully selecting substrate components and insulation materials to minimize environmental impacts over the green roof life cycle.

An LCA approach to evaluate the environmental impact of different modular roof systems (precast hollow-core concrete, composite, steel, and wood) for a large-span industrial building in Calgary, Alberta, was presented by Alshamrani [26]. The author analyzed a 65,000 sq. ft. industrial building using LCA (ATHENA software) tools. The LCA indicated the precast roof system had the highest global warming potential (GWP) of 28.3 million kg CO₂-eq. over 30 years, primarily from the operating stage (90% of total). The wood roof system had the lowest GWP of 3.5 million kg CO₂-eq., around 88% lower than precast. The steel roof system had the second-lowest GWP of 6.1 million kg CO₂-eq., 78% lower than precast. The authors concluded that the wood and steel roof systems demonstrated substantially lower energy consumption, greenhouse gas emissions, and environmental impacts compared to precast and composite roofs across all life cycle stages. Shafique et al. [27] provided an overview of LCA studies on green roofs to evaluate their environmental impacts and identify sustainable design practices. The authors conducted a systematic literature review, analyzing 53 research articles published between 2006 and 2019 that applied LCA to green roof systems. They found that the most LCA studies on green roofs were conducted in Europe (54%), followed by the USA (15%), Canada (9.4%), and China (5.7%). The most common functional unit was roof area (m²), and the typical lifetime analyzed was 30–50 years. SimaPro was the most widely used LCA software (30%), followed by CML2000 (21%), ReCiPe (13%), and IMPACT 2002+ (13%). Global warming potential and ozone depletion potential were the most frequently evaluated environmental impact categories. Roy et al. [28] conducted an LCA analysis of steel roofing systems, including ancillary items like gutters and flashings, for a residential house in New Zealand. The functional unit was taken as 1 m² of steel roofing covering for a high wind zone over 60 years. The system boundary included production, transportation, end-of-life, and recycling potential stages. The results showed that for 1 m² over 60 years, the total global warming potential was 10.6 kg CO₂-eq., with production contributing 9.97 kg CO₂-eq. It was noted that steel roofing contributed the most to acidification, eutrophication, and abiotic resource depletion impacts.

Balasbaneh et al. [29] conducted an LCA and life cycle cost (LCC) analysis for different wall and roof designs of residential buildings in Malaysia over a 50-year lifespan. The authors evaluated five alternative wall schemes (W1–W5) and four roof combinations (R1-R4) using SimaPro 8.3 LCA software and LCC analysis. The results for walls showed that the timber wall scheme W5 (wooden post and beam covered by steel stud) had the lowest environmental impact, releasing 1320 kg CO₂-eq over its lifetime. For roofs, the wood truss with concrete roof tiles had the lowest emissions of 3840 kg CO₂-eq. The comprehensive review by Vijayaraghavan [30] on green roofs delved into the benefits, challenges, and components essential for their successful implementation. The study underscored the importance of selecting appropriate vegetation and substrates, which significantly influence stormwater management, energy savings, and the mitigation of urban heat island effects. It highlighted the diverse range of materials explored for use in substrates, including low-cost, lightweight options like crushed bricks and biochar aimed at optimizing water retention, nutrient filtering, and plant growth support. Carretero-Ayuso and García-Sanz-Calcedo [31] compared different roof construction systems using LCA techniques, considering environmental impacts like embodied energy, CO₂ emissions, and waste generation, as well as socio-economic factors such as cost, labor time, maintenance requirements, and execution risk. The results showed that for embodied energy use, flat roofs with concrete slabs had the highest values, while pitched tile roofs were in the mid-range. CO₂ emissions followed a similar pattern, with flat roofs having the highest emissions. The waste generation was noted to be the highest for pitched tile roofs and lowest for most flat roofs.

El Bachawati et al. [32] conducted a cradle-to-gate LCA analysis comparing the environmental impacts of a traditional gravel ballasted roof (TGBR), white reflective roof (WRR), extensive green roof (EGR), and intensive green roof (IGR) for a building in Lebanon. They quantified impacts across 15 LCA categories like global warming potential, ozone depletion, ecotoxicity, and resource depletion. The results showed that for TGBR, the major contributors were rebar, concrete, and pebbles due to emissions from production processes like mineral extraction and fossil fuel use. For WRR, rebar, concrete, and thermal insulation were the sources with the highest impact. For EGR and IGR, the main contributors were rebar, concrete, waterproof membrane, thermal insulation, and perlite (for IGR) due to extraction and production processes. Pakdel et al. [33] conducted a cradle-to-gate LCA comparing the embodied energy and CO₂ emissions of a traditional Iranian construction system (TTM) and a contemporary construction system (CSM) for a school building in Yazd, Iran. The LCA quantified the environmental impacts across the material production, construction, and operational use. The authors reported that in the material production phase, TTM had lower embodied energy (1032 GJ) and CO₂ emissions (66 tonnes) compared to CSM, with 2456 GJ and 167 tonnes of CO₂, respectively, due to TTM’s use of natural materials like adobe and mud. In the construction phase, TTM again had lower energy use (18 GJ) and emissions (1.1 tonnes CO₂) versus CSM at 112 GJ and 7 tonnes CO₂, attributed to TTM’s simpler construction techniques. For operational energy use over 50 years, CSM consumed 5844 GJ for HVAC, lighting, and hot water, while TTM only used 1032 GJ for lighting and hot water since it relies on passive cooling/heating. Susca [34] proposed an enhancement to the LCA methodology by incorporating the effect of surface albedo on climate change. The study developed a time-dependent climatological model to quantify the impact of surface albedo variation on global warming potential (GWP) in terms of CO₂-eq. The model provided a time-dependent equivalence between a 0.01 increase in surface albedo per square meter and the corresponding decrease in CO₂ equivalents. For a 50-year time horizon, a 0.01 increase in surface albedo decreases CO₂ equivalents by 2.45 kg.

Carvalho et al. [35] investigated the carbon footprint associated with a 0.52 kWp mono-crystalline silicon (mono-Si) photovoltaic ceramic roof tile system compared to a traditional photovoltaic panel system. The study showed that the mono-Si photovoltaic roof tile system had a carbon footprint of 1160 kg CO₂-eq., and the traditional photovoltaic panel system had a slightly lower carbon footprint of 950 kg. The study concluded that while the traditional panel system had a slightly lower carbon footprint, building-integrated photovoltaic (BIPV) roof tiles could be favored from an architectural perspective by harmonizing with the surroundings. Pierobon et al. [36] conducted a cradle-to-gate LCA comparing the environmental impacts of a hybrid cross-laminated timber (CLT) office building to a reinforced concrete building in the U.S. Pacific Northwest. The results showed that the hybrid CLT building achieved an average 26.5% reduction in global warming potential compared to the concrete building when excluding biogenic carbon emissions. The total primary energy demand was similar between building types, but the non-renewable (fossil) energy use was 8% lower for the hybrid CLT building. The authors highlighted the environmental benefits of using hybrid CLT construction for mid-rise non-residential buildings in the U.S. Pacific Northwest region, especially in reducing global warming impacts through lower embodied emissions and carbon storage in wood. Islam et al. [37] conducted an analysis of different roofing and flooring designs in residential buildings in Australia. The LCA results showed that the operation phase contributed the highest greenhouse gas (GHG) emissions (53–68%) and cumulative energy demand (CED) (52–64%) across all designs evaluated. The construction phase had the second-highest impact, contributing 31–44% of GHG emissions and 31–43% of CED, and the maintenance phase contributed 4–6% of GHG emissions, 5–6% of CED, and 20–36% of water use.

Pons Fiorentin et al. [38] conducted a comprehensive review of LCA studies on green roofs. For most of the studies (75%), the authors found that impact assessment methods like ReCiPe, CML, and IMPACT 2002+ were used. Climate change was the most commonly assessed impact category across all studies, with 60% of studies relying solely on secondary data from databases, while 40% used a mix of primary and secondary data. Further, a quantitative analysis of 31 green roof occurrences from 16 studies showed a wide range of climate change impacts per m² of green roof area, and the key contributors were found to be the green roof materials (drainage, substrate, vegetation layers) and life cycle stages like construction. The review highlighted the variability in LCA methods applied to green roofs and the need for standardization and primary data to improve the reliability of results on their environmental performance. Costa et al. [39] systematically reviewed LCA and carbon footprint (CF) studies of wood-based panels. The authors found that 37 studies applied LCA up to the impact assessment phase, 6 focused only on climate change/CF, and 1 used the ecological footprint method. Additionally, 60% of studies relied solely on secondary data from databases like Ecoinvent, while 40% used a mix of primary and secondary data. System boundaries varied, with 48% cradle-to-grave, 25% cradle-to-use, 13% cradle-to-gate, and 15% cradle-to-manufacturer. Gargari et al. [40] evaluated the environmental impacts of four different green roof solutions compared to a standard clay-pitched roof using LCA analysis. The study assessed different green roof types, i.e., extensive with high-density (HD) and low-density (LD) growing medium and intensive with HD and recycled growing medium. The results showed that green roofs generally have 20–30% lower depletion of abiotic resources such as fossil fuels, 5–6% lower ozone depletion potential, and around 5% lower impacts like acidification and eutrophication potential compared to the clay-pitched roof. For intensive green roofs, the growing medium accounted for 7–15% of global warming potential, 15–20% of acidification potential, and 20–25% of eutrophication potential. Further, using recycled materials like bricks in the growing medium (as in the intensive green roof with recycled medium) significantly reduced impacts like acidification and global warming potential.

H. Wu et al. [41] conducted a life cycle carbon emissions assessment for building decoration of an office building case study. The total carbon emissions during the building decoration life cycle were reported as 1654 tons CO₂-eq., with an intensity of 82.7 kg CO₂-eq./m². The materials’ embodied impact stage contributed the highest emissions at 600.3 tons CO₂-eq. (36.3%), with flame-retardant plates, square steel, cement mortar, and ceramic tiles being the major contributors. Finally, the operation stage accounted for 49.0% of total emissions. The authors emphasized the importance of reducing carbon emissions from the material production and operation stages for sustainable building decoration. Ji et al. [42] investigated the LCA of six roof-waterproofing systems [asphalt (C1), synthetic polymer-based sheet (C2), improved asphalt (C3), liquid applied membrane (C4), metal sheet with asphalt sheet (N1), and liquid applied membrane with asphalt sheet (N2)] for a reinforced concrete building using an architectural model. The results showed that considering only materials and energy demands for waterproofing systems per square meter during the construction phase, higher greenhouse gas (GHG) emissions were generated in the order of C1 > N2 > C4 > N1 > C2 > C3. Further, when considering the entire life cycle including construction, maintenance, and deconstruction, the amount of GHG emission was in the order of C4 > C1 > C3 > N2 > C2 > N1, with N1 being the most environmentally friendly. The authors pointed out the importance of considering the full life cycle, including maintenance requirements, when selecting a roof waterproofing system to minimize environmental impacts like GHG emissions. Another study [43] conducted an LCA analysis of a mass timber residential building using cross-laminated timber (CLT) and a functionally equivalent concrete residential building in China. The study aimed to quantify the potential environmental benefits of using CLT as an alternative to concrete. The results showed that timber buildings achieved a 25% reduction in global warming potential compared to concrete buildings, primarily due to lower impacts from material production. The authors concluded that the lighter mass of materials offset the higher transportation impacts, resulting in lower greenhouse gas emissions for the timber building.

Morau et al. [44] conducted an LCA study to evaluate the environmental impacts of extensive and intensive green roof systems implemented in a low-income country in the global south. The study analyzed the impacts of different layers and materials used in green roofs, including the production, transportation, and use phases. The authors found that non-treated and imported materials like cement, virgin plastics, and soil have higher environmental impacts compared to recycled or locally sourced materials. The substrate layer, comprising soil and organic fertilizers, significantly contributes to impacts, especially for intensive green roofs, due to larger quantities required, and using natural fertilizers like poultry manure instead of synthetic fertilizers could help reduce the impacts for the substrate layer. Napolano et al. [45] assessed the environmental impacts of three alternative flat roof systems (reinforced concrete, steel, and polystyrene) to replace an existing wooden flat roof on a residential masonry building using LCA. The study considered the construction, use, maintenance, and end-of-life phases over a 60-year lifetime. For the construction phase, concrete was found to be the main material used across all options (>60% by weight), followed by light concrete, bricks, and steel. The LCA results showed the polystyrene option had the lowest environmental impacts across most categories due to the benefits of polystyrene recycling. Katebi et al. [46] evaluated the environmental impacts of different roof systems using LCA. The authors assessed several roof types, i.e., concrete slab, Uboot concrete slab, concrete beams with polystyrene blocks, chromite beams with polystyrene blocks, concrete beams with clay blocks, chromite beams with clay blocks, and concrete beams with concrete blocks. It was noted that the Uboot concrete slab roof had the highest environmental impacts across global warming potential (15% higher than other roofs), eutrophication potential (17.4–18.7% higher), and acidification potential (15.8% higher). Chippagiri et al. [47] presented an LCA study of a sustainable prefabricated housing system using a cradle-to-site approach based on a small-scale experimental model. The study aimed to evaluate the environmental implications of the proposed system, which incorporated various sustainable alternatives in the mix designs. The authors used locally available agro-industrial waste called co-fired ash (CFA) as a partial replacement for fine aggregates in concrete and lightweight (LW) mixes. The results showed that the optimized mix designs for CFA-based concrete and LW mix achieved densities of 2342 kg/m³ and 1312 kg/m³, respectively, with satisfactory strength and thermal properties. The study demonstrated the successful construction of a small-scale prefabricated model house using the proposed sustainable materials and mixed designs.

A summary of LCA studies investigating the environmental impact of different roofing systems is presented in

Table 2. Review of LCA studies of different roofing systems.

Year	Location	Focus	Key Findings	Ref.
2022	-	Green Roof Layers and Materials	Polyethylene root barrier had lower impacts than PVC; light non-woven polypropylene protection layer had lower impacts than heavy version; recycled high-impact polystyrene drainage layer had lower impacts than virgin material; recycled textile fibers for water retention layer had lower impacts than rock wool; zeolite among lightweight soil components had highest impact; recommendation for using recycled materials and simple green roof design to reduce environmental impacts	[20]
2012	Italy	Extensive Green Roof System	Growing medium composition significantly influenced environmental impacts, with fertilizers used for maintenance contributing most to eutrophication and terrestrial ecotoxicity; disposal of growing medium and bitumen in landfills during end-of-life had the highest impacts on human toxicity and marine aquatic ecotoxicity	[21]
2019	France	Different Roof Systems	Consideration of “ex situ” biodiversity impacts, particularly for conventional roofs; intensive green roofs demonstrated 37% lower impact than conventional roofs per ReCiPe; the importance of considering biodiversity impacts to preserve biodiversity during the building’s life cycle	[22]
2014	-	Environmental Benefits of Green Roofs	Green roofs reduce roof surface and ambient air temperature compared to conventional roofs; increasing vegetation density improves energy performance benefits across different cities; complex heat and mass transfer processes influence the thermal performance of green roofs	[23]
2007	United States	Life Cycle Assessment of Green Roofs	Extensive green roofs have lower environmental impacts across categories like acidification, eutrophication, and global warming potential compared to conventional roofs when accounting for reduced operational energy use; operational benefits offset higher upfront material and installation impacts over the full life cycle	[24]
2017	Czech Republic	Semi-Intensive Green Roof Assembly Configurations	Assembly with XPS insulation had the highest impacts in categories like global warming potential due to energy-intensive XPS production; mineral wool panels as near-total substrate replacement had the highest impacts on acidification and eutrophication potentials; the importance of selecting substrate components and insulation materials to minimize the environmental effects over green roof life cycle	[25]
2021	Canada	Modular Roof Systems	Wood and steel roof systems demonstrated substantially lower energy consumption, greenhouse gas emissions, and environmental impacts compared to precast and composite roofs across all life cycle stages	[26]
2020	-	Overview of LCA Studies on Green Roofs	An increasing trend in LCA studies on green roofs over the past decade; the importance of using safer, more sustainable materials and optimizing design for reduced lifecycle impacts	[27]
2022	New Zealand	LCA Analysis of Steel Roofing Systems	Steel roofing systems contribute significantly to acidification, eutrophication, and abiotic resource depletion impacts over their life cycle; recommendations provided to improve the accuracy and completeness of environmental assessments for steel roofing systems in New Zealand	[28]
2018	Malaysia	LCA and LCC Analysis for Residential Buildings	Timber-based wall and roof design (W5R1) was identified as the optimal sustainable choice for residential construction in Malaysia to minimize carbon footprint and life cycle costs	[29]
2016	-	Review of Green Roofs	Importance of selecting appropriate vegetation and substrates for stormwater management, energy savings, and mitigation of urban heat island effects; the potential of green roofs to improve air and water quality in urban areas	[30]
2018	Spain	Comparison of Roof Construction Systems	Trade-offs between different roof systems in terms of environmental impacts, economic factors, and practical considerations; consideration of embodied energy use, CO2 emissions, waste generation, cost, labor time, maintenance requirements, and execution risk	[31]
2016	Lebanon	LCA Analysis of Roof Types	Green roofs are preferable over conventional roofs due to reduced energy demand and extended roof membrane life; growing medium composition significantly influences environmental impacts	[32]
2021	Iran	Comparison of Traditional and Contemporary Construction Systems	Traditional Iranian construction methods like TTM demonstrated significant environmental benefits compared to contemporary energy-intensive construction due to the use of low-impact natural materials and passive design strategies	[33]
2012	United States	Impact of Surface Albedo on Climate Change	Incorporating surface albedo effects enhances LCA methodology by accounting for key properties influencing climate change impacts; demonstrated the potential of high-albedo surfaces like white roofs to offset CO2 equivalents	[34]
2019	Brazil	Carbon Footprint of Photovoltaic Roof Systems	Building-integrated photovoltaic roof tiles offer architectural benefits despite a slightly higher carbon footprint compared to traditional photovoltaic panel systems; potential reduction in carbon footprint by using poly-crystalline silicon cells in roof tiles	[35]
2019	U.S. Pacific Northwest	LCA Comparison of Hybrid CLT and Concrete Buildings	Hybrid cross-laminated timber (CLT) construction achieved a significant reduction in global warming potential compared to reinforced concrete buildings, primarily due to lower embodied emissions and carbon storage in wood	[36]
2015	Australia	LCA and LCC Analysis of Roofing and Flooring Designs	Higher star-rated designs like gable tile roofs and skillion flat roofs perform better when considering greenhouse gas emissions, cumulative energy demand, and life cycle costs together	[37]
2024	-	Review of LCA Studies on Green Roofs	Variability in LCA methods applied to green roofs; need for standardization and primary data to improve reliability of results on environmental performance	[38]
2024	-	Systematic Review of LCA Studies of Wood-Based Panels	Wide range of climate change impacts per m2 of wood-based panel area across studies; key contributors identified as materials and life cycle stages like construction	[39]
2016	Italy	Environmental Impacts of Green Roof Solutions	Green roofs generally have lower impacts compared to conventional roofs; the importance of growing medium composition, particularly using recycled materials, in reducing impacts	[40]
2023	China	Life Cycle Carbon Emissions Assessment for Building Decoration	Total carbon emissions during the building decoration life cycle, mainly from materials’ embodied impact stage; the importance of reducing emissions from materials production and operation stages for sustainable building decoration	[41]
2014	South Korea	LCA of Roof-Waterproofing Systems	Importance of considering the full life cycle, including maintenance requirements, when selecting roof waterproofing systems to minimize environmental impacts like greenhouse gas emissions	[42]
2022	China	Comparison of LCA of Mass Timber with Concrete Residential Buildings	The potential environmental benefits of using CLT as an alternative showed that timber buildings achieved a 25% reduction in global warming potential compared to concrete buildings, primarily due to lower impacts from material production.	[43]
2017	Global south	LCA of Extensive and Intensive Green Roof Systems	Non-treated and imported materials like cement, virgin plastics, and soil have higher environmental impacts compared to recycled or locally sourced materials. The substrate layer significantly contributes to impacts, especially for intensive green roofs, due to the larger quantities required	[44]
2015	Italy	LCA of Three Flat-Roof Systems	The polystyrene option had the lowest environmental impact across most categories due to polystyrene recycling benefits. Reductions in concrete consumption are effective for lowering eutrophication impacts, and reductions in rebar consumption can lower acidification impacts for most roof types.	[45]
2023	Iran	Environmental Impacts of Various Roof Types	Uboot concrete slab roofs had the highest environmental impact across global warming, eutrophication, and acidification potentials. Concrete and chromite beam roofs with polystyrene blocks generated the least environmental impact.	[46]
2023	India	LCA of a Sustainable Prefabricated Housing System Using Agro-industrial Waste	The successful construction of a small-scale prefabricated model house using optimized mix designs for CFA-based concrete and LW mix, achieving satisfactory strength and thermal properties.	[47]

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3.3. Whole-Building LCA

While individual LCA studies focusing on specific building materials or components offer valuable insights, there is a growing acknowledgment of the importance of adopting a more comprehensive, whole-building life cycle approach. Whole-building LCA quantifies the complete environmental impacts of buildings throughout their entire life cycle, encompassing factors such as material manufacturing, construction, operation, maintenance, and end-of-life phases. It is essential to conduct a comprehensive literature review of whole-building LCA studies to gain insights into current practices, identify key methodological challenges and gaps, and guide the development of more robust and standardized approaches. This section delves into the state-of-the-art in whole-building LCA, synthesizing findings from diverse case studies spanning various building types, geographic regions, and system boundaries.

Vilches et al. [48] reviewed LCA studies on building refurbishment to analyze the methodological approaches used and identify best practices. Most studies focused on residential buildings (single-family and multi-family dwellings) with functional units varied—per m² of living area, per building, per year of use, etc. The environmental impact categories included energy demand, global warming potential (GWP), acidification, eutrophication, etc. The results showed that the refurbishment reduced operational energy by 30–82% compared to no retrofit. Alotaibi et al. [49] conducted an LCA study focusing on embodied carbon and evaluated strategies for the decarbonization of a high-rise residential building in an urban region of India. The study adopted a BIM-based LCA i.e., considering a cradle-to-grave system boundary including material manufacturing, construction, operation, and end-of-life stages. The functional unit was a high-rise residential building with 30 floors, 56 dwelling units, and a 75-year reference service life. The results for the base case building illustrated the embodied carbon emissions at 414 kg CO₂-eq./m²/year or 14,196 kg CO₂-eq/m² over the service life. The authors suggested that the integration of BIM and LCA can provide a systematic approach to quantify embodied carbon and assess decarbonization strategies for reducing the environmental impact of high-rise residential buildings over their life cycle. Di Santo et al. [50] presented an approach for assessing buildings’ environmental impact and user comfort from the early design stage, combining LCA, building information modeling (BIM), and the Active House protocol. The study proposed a method that integrates a BIM-based quantity take-off for material quantities, an Excel-based Active House LCA (AH-LCA) tool for environmental impact assessment, and the Active for the First Design option; the results showed a global warming potential of 5.6 kg CO₂-eq./m²/year for construction and 51.8 kg CO₂-eq./m²/year for operation. The second design option, with refinements to the building envelope and materials, achieved a reduction in the global warming potential for construction to 2.3 kg CO₂-eq./m²/year but a slight increase in operational energy demand for space heating. The authors demonstrated the effectiveness of the proposed method in integrating BIM, LCA, and sustainability criteria for early-stage building design assessments, enabling informed decision-making and promoting more sustainable building solutions.

Kamali et al. [51] conducted a comparative cradle-to-gate LCA study of conventional and modular construction methods for residential buildings. The study evaluated the environmental impacts during the material production and construction phases for three case study buildings: a conventionally built house (Conv) and two modular houses (Mod1 and Mod2). The LCA quantified eight environmental impact measures: global warming potential, acidification potential, human health effects, eutrophication potential, ozone depletion potential, smog potential, fossil fuel consumption, and eco-toxicity effects. It was noted that during the construction phase, Mod1 outperformed Conv and Mod2 across all impact measures due to lower energy consumption during off-site construction and transportation activities. In the material production phase, Mod1 had higher impacts than Conv and Mod2 for some measures like global warming potential and acidification potential. For the overall cradle-to-gate life cycle, Mod1 ranked first, exhibiting the lowest environmental impacts across different weighting schemes used to aggregate the impact measures into a single index. Evangelista et al. [52] evaluated the environmental performance of four typical Brazilian residential buildings with different typologies using a “cradle to grave” LCA study. The authors found that the operational phase had the greatest environmental impacts, exceeding 80% in several impact categories. The foundation, structure, masonry, and coating subsystems had the greatest environmental impacts during the construction phase. In terms of materials, concrete, ceramic tiles, and steel made the largest contributions to the environmental impacts. Rinne et al. [53] conducted a comparative study on the life cycle assessment and carbon footprint of a five-story hybrid apartment building that utilized concrete for the main load-bearing system and cross-laminated timber (CLT) for exterior cladding and the top floor, along with timber and reinforced concrete counterparts, in Finland. The study used a whole-building LCA approach with the One Click LCA software tool to analyze the environmental impacts over a 50-year lifespan. The timber apartment building was found to have the lowest overall life cycle emissions at 1,215,038 kg CO₂-eq., which was 6.6% lower than the hybrid building and 6% lower than the concrete building. The hybrid and concrete apartment buildings had similar total emissions, with the concrete building slightly lower at 1,293,345 kg CO₂-eq. (0.6% less than the hybrid). The hybrid building had a higher potential for benefits beyond the building life cycle at 167,572 kg CO₂-eq., which was 47.2% higher than the timber building and 27.8% higher than the concrete building.

Rabani et al. [54] evaluated the greenhouse gas (GHG) emissions from retrofitting an existing Norwegian office building to different energy performance levels using LCA methodology. The study analyzed the emissions associated with various building materials, components, and systems across different life cycle stages for a reference case and several retrofit scenarios aiming for nearly zero-energy building (nZEB) or passive house (PH) standards. It was noted that for the reference building, the largest contributors to embodied emissions were concrete (35%), reinforced steel (27%), and insulation materials (12%). The most significant emission sources were the product stage at 46% and operational energy use at 43% over the 60-year lifetime. Asif et al. [55] conducted a life cycle primary energy analysis of multi-story wood-framed buildings with different structural solutions for load-bearing systems and facade claddings. The study compared the primary energy use for the production, operation, and end-of-life treatment of a wood-frame multi-story building to functionally equivalent buildings with load-bearing systems of concrete and steel. Different facade claddings like wood, brick, and rendering on insulation were also evaluated. It was found that the wood-frame building had 60–90% lower embodied primary energy than the concrete and steel buildings over the life cycle. Also, for a 50-year lifetime, the total primary energy use was 30–60% lower for the wood-frame building compared to concrete and steel alternatives. The results highlighted the environmental benefits of using wood-based construction systems and claddings, which can significantly reduce the life cycle primary energy demand of multi-story residential buildings. Li et al. [56] investigated the challenges and proposed solutions for the reliable life cycle carbon assessment (LCCA) of prefabricated buildings. The study found that the implicit system boundaries of prefabrication and LCCA lead to inconsistent methods and models. The authors proposed a regression model relating buildings’ LCCA to 12 system boundaries, expressed by the system boundaries’ inconsistency ratio. They further developed a five-level framework of units of analysis: material, component, assembly, flat, and building to enhance the reliability and validity of LCCA research on prefabricated buildings for effectively reducing their life cycle carbon emissions.

T. Wu et al. [57] conducted a preliminary sensitivity study on a life cycle assessment (LCA) tool by assessing a hybrid timber building. The study used the Athena IE4B LCA software to analyze two cases. Case 1 focused on changing only the volume of wood materials by ±20%, ±10%, and +50%, and the results showed that increasing wood materials increased all environmental indicators, with global warming potential being the least sensitive indicator. Case 2 focused on simultaneously changing the volumes of wood, steel, and concrete materials proportionally by ±20%, ±10%, and +50%. The results showed that proportionally increasing wood materials relative to steel and concrete resulted in a reduction in all environmental indicators, with eutrophication and ozone depletion being the most sensitive and least sensitive indicators, respectively, to the proportional material changes. AL-Nassar et al. [58] developed a sustainability assessment framework to compare different wall–roof material combinations for low-rise commercial buildings using a life cycle impact index (LCII) approach. The study evaluated six building alternatives: steel–steel system, concrete–steel system, steel–wood system, wood–wood system, wood–steel system, and concrete–wood system. The results showed that for the environmental life cycle impact score, steel–wood had the lowest score of 0.102, making it the most sustainable alternative environmentally. The authors emphasized the importance of weighing the triple bottom-line dimensions based on organizational priorities when evaluating the sustainability of building material choices. Akyüz et al. [59] investigated the economic and environmental optimization of wall and roof insulation for an airport terminal building in Turkey. The authors calculated the optimum insulation thickness and associated payback periods using degree-day methods and LCA. For the economic analysis, optimum insulation thicknesses were calculated as 0.0502 m for the walls and 0.0734 m for the roof to minimize heating and cooling costs over a 20-year lifetime. The economic payback times were found to be 6.38 years for the walls and 7.02 years for the roof. In terms of greenhouse gas, the payback time was noted to be 4.09 years for the walls and 2.09 years for the roof.

Trovato et al. [60] presented an economic–environmental valuation of an energy retrofit project for a public building in a Mediterranean area, integrating an LCA into the traditional economic–financial evaluation. The proposed retrofit strategies included wooden double-glazed windows, organic external wall insulation systems (CorkPan), and green roofs. The results showed that the strategies can reduce energy needs for heating by 58.5% and cooling by 33.4%. Using sustainable materials like CorkPan reduced the building’s carbon footprint index by 54.1% after retrofit compared to standard materials. Z. Chen et al. [61] conducted a comparative LCA study of a high-rise mass timber (MT) building with an equivalent reinforced concrete (RC) alternative using the Athena Impact Estimator for Buildings (IE4B) tool. The study compared the environmental impacts of the two 12-story mixed-use building designs over 60 years. The results showed that the MT building had lower total embodied carbon emissions of 1.70 × 10⁷ kg CO₂-eq. compared to 2.15 × 10⁷ kg CO₂-eq. for the RC building from cradle to grave. When considering end-of-life reuse, recycling, and energy recovery, the MT building’s total emissions were reduced to 6.57 × 10⁶ kg CO₂-eq., while the RC building’s emissions increased to 2.16 × 10⁷ kg CO₂-eq. Mohebbi et al. [62] investigated the impact of using different embodied carbon factor (ECF) databases on the accuracy of life cycle assessment (LCA) calculations for the embodied carbon of buildings. The study conducted an LCA for a standard 2500 m² single-story Lidl supermarket in the UK using a BIM model. The results showed that using the UK Department of Energy & Climate Change database with limited material ECFs resulted in a total embodied carbon of 2,326,495 kg CO₂-eq. for the supermarket. The study underscored the need for standardized, comprehensive national databases and EPDs to improve the reliability and comparability of embodied carbon assessments.

A summary of studies investigating the whole-building LCA to quantify the complete environmental impacts of buildings is summarized in

Table 3. Review of studies on whole-building LCA.

Year	Location	Focus	Key Findings	Ref.
2017	-	Building refurbishment	Refurbishment reduced operational energy by 30–82%; improving building envelope insulation yielded significant energy benefits; embodied energy payback times ranged from 0.01–4.8 years, emphasizing the need for standardized LCA practices tailored to building refurbishment.	[48]
2022	India	Decarbonization of high-rise residential building	Adopted BIM-based LCA approach, reducing embodied carbon to 135 kg CO2-eq./m2/year with decarbonization strategies; integration of BIM and LCA enables systematic assessment of decarbonization strategies for high-rise residential buildings.	[49]
2023	Italy	Environmental impact assessment of early-stage building design	Integrated BIM, LCA, and Active House protocol for early-stage building design assessment, achieving reductions in global warming potential through envelope and material refinements, highlighting the effectiveness of the proposed method for informed decision-making.	[50]
2019	Canada	Comparative LCA of conventional vs. modular construction	Modular construction outperformed conventional in the construction phase but had varied impacts in material production; modular construction’s overall cradle-to-gate life cycle impacts depend on materials, energy use, and transportation.	[51]
2018	Brazil	LCA of typical Brazilian residential buildings	The operational phase had the greatest environmental impacts; foundation, structure, masonry, and coating subsystems were key contributors during construction; concrete, ceramic tiles, and steel made the largest material contributions; low-standard dwellings had the highest impacts per unit area; operational phase dominates the impact across different Brazilian residential typologies.	[52]
2022	Finland	Comparative LCA of hybrid vs. timber vs. concrete apartment building	Timber buildings had the lowest overall life cycle emissions, demonstrating environmental advantages; the hybrid building had potential benefits beyond the life cycle, highlighting the role of hybrid solutions in reducing emissions compared to traditional concrete buildings.	[53]
2021	Norway	GHG emissions from retrofitting a Norwegian office building	Embodied emissions are mainly from concrete, steel, and insulation; retrofitting to all-air constant air volume resulted in the lowest total emissions, showcasing the importance of material selection and system efficiency in retrofit strategies.	[54]
2007	Scotland	LCA primary energy analysis of wood-framed vs. concrete/steel buildings	Wood-frame buildings had significantly lower embodied primary energy over the life cycle, with operational energy dominating; wood cladding further reduced embodied energy; highlighted the environmental benefits of wood-based construction systems.	[55]
2018	-	Challenges and solutions for reliable LCCA of prefabricated buildings	Proposed regression model and five-level framework to enhance reliability and validity of LCCA research on prefabricated buildings, addressing implicit system boundary inconsistencies and offering a systematic approach for reducing life cycle carbon emissions of prefabricated buildings.	[56]
2020	United States	Sensitivity study of LCA tool on hybrid timber building	A preliminary study using Athena IE4B software showcased the sensitivity of environmental indicators to material choices, indicating the feasibility of software for initial LCA analysis to understand the impact of material choices.	[57]
2016	Canada	Sustainability assessment of wall–roof material combinations	The steel–wood system was identified as the most sustainable environmentally; the concrete–steel system was most economical; emphasized the importance of organizational priorities in weighing triple bottom-line dimensions when evaluating building material choices.	[58]
2017	Turkey	Economic and environmental optimization of wall and roof insulation	Insulating terminal building envelope was found to be environmentally favorable, with energy and emissions savings outweighing production impacts within a few years; emphasized the role of insulation in reducing energy consumption and emissions in buildings.	[59]
2020	Italy	Economic–environmental valuation of energy retrofit project	Retrofit strategies reduced energy needs and carbon footprint; sustainable materials increased socio-environmental–economic–financial results; tax benefits are crucial for cost savings and environmental benefits, highlighting the importance of policy support.	[60]
2020	United States	Comparative LCA of mass timber vs. reinforced concrete building	Mass timber buildings had lower embodied carbon emissions, stored more CO2, and displaced fossil-fuel-intensive materials, indicating a lower embodied carbon footprint of timber building design.	[61]
2021	United Kingdom	Impact of ECF databases on LCA accuracy for building embodied carbon	The choice of the ECF database significantly impacts embodied carbon calculations, emphasizing the need for standardized, comprehensive databases to improve the reliability and comparability of embodied carbon assessments.	[62]

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4. Conclusions and Future Work

LCA offers a valuable framework for evaluating the environmental impacts of roofing materials and informing sustainable construction practices. By considering all stages of a material’s life cycle, from raw material extraction to end-of-life disposal, LCA provides insights into energy consumption, greenhouse gas emissions, resource depletion, and other environmental indicators associated with different roofing materials. Through a comprehensive review of existing LCA studies, this review has synthesized key findings, identified challenges, and proposed future directions for research and sustainable practices in the construction industry. By integrating LCA findings into decision-making processes, designing for longevity and durability, promoting recycling and reuse, and embracing alternative materials and innovative solutions, stakeholders can advance sustainable construction practices and contribute to the transition towards a more sustainable built environment.

A crucial observation from the review is the limited number of studies exploring LCA at the urban scale for roofing components. This gap presents a significant opportunity for future research to utilize LCA at broader urban scales, which can offer a more complete understanding of the environmental impacts associated with roofing materials in urban settings. It is essential to have a more comprehensive analysis that considers various materials and stages of their life cycle, including social and economic factors.

It is important to emphasize the often-underutilized potential of roofs in urban environments. Beyond their primary protective function, roofs hold numerous opportunities for enhancing urban sustainability. The review has also highlighted potential biases in existing studies that may overrate certain solutions, such as green roofs. While green roofs offer benefits in terms of thermal performance and carbon sequestration potential, it is crucial to consider factors like maintenance requirements and structural limitations, especially in refurbishment projects. For instance, the building structure of existing buildings might not support the load of some theoretically optimal constructive solutions. This underscores the importance of adopting a more comprehensive view when evaluating roofing options.

To address these challenges, it is recommended to have a more holistic approach to roofing LCA studies. Future research should aim to integrate environmental, social, and economic factors into assessments. This approach would provide a more nuanced understanding of the overall sustainability of roofing solutions, going beyond just environmental impacts to consider practical implementation issues. Further, it is important to focus on actual case studies. While theoretical approaches provide valuable insights into environmental performance, case studies can bridge the gap between theory and practice. They can offer real-world examples of how different roofing solutions perform under various conditions, accounting for factors that may be overlooked in purely theoretical assessments.

In conclusion, while current LCA studies in the roofing industry provide valuable information on environmental impacts, there is a clear need for more comprehensive, holistic approaches. Future research should strive to incorporate broader urban-scale assessments, consider the multifunctional potential of roofs, and integrate practical implementation factors. By doing so, we can develop a more robust understanding of roofing sustainability, supporting informed decision-making in both new construction and refurbishment projects and ultimately contributing to more sustainable urban environments.