**1. Introduction**

In recent years, the use of green roofs has increased, not only for aesthetic reasons but also to improve the environmental quality of the environment [1]. Plants can reduce heat through the reflection of solar radiation and the generation of shade. They can also decrease heat through the evapotranspiration process, which reduces the temperature inside and outside buildings [2]. In this way, green roofs are considered a modern and ecological technology to face climate change and the most common environmental problems in the urban environment [3]. Green roofs represent the opportunity to expand the presence of vegetated surfaces by replacing conventional waterproofed surfaces, generating thermal insulation, improving the internal environment of buildings, and consequently causing a reduction in the energy consumption of such buildings [4,5].

Though green roofs have the benefits described above, their use in many countries is limited due to costs and environmental impacts of using non-renewable materials, as well as the lack of formal methods focused on their design, construction, and maintenance [6]. A growing trend regarding the construction of green roof systems has been the use of recycled and reused materials in their drainage

and substrate layers, which can generate environmental, technical, economic, and aesthetic benefits while also providing the possibility of incorporating waste into the construction production chain. Most of the existing works in the current literature regarding the use of recycled materials in green roofs have sought to evaluate their hydraulic performance (drainage capacity and water retention) and the response of vegetation growth compared to conventional green roof systems. Table 1 summarizes the most relevant works concerning the use of recycled materials in green roofs. Recycled materials such as rubber, glass, and construction waste have been widely studied in the last decade, demonstrating that replacing conventional green roof materials is a feasible solution.


**Table 1.** Summary of works related to the use of recycled materials in green roofs.

To contribute to these research efforts, the present study aimed to evaluate the performance of green roofs with drainage layers made out of recycled and reused materials for reducing the impact on virgin materials and assuring technical benefits such as temperature reduction, water retention, and the regulation of rainwater. In addition, this study analyzed the reduction of dead load compared to traditional green roofs, which is relevant in terms of building structures. The subsequent sections of this paper are organized as follows: Section 2 summarizes the materials and methods employed to conduct the experimentation and to analyze the hydraulic and thermal performance of the proposed green roof systems. Results are presented in Section 3, while Sections 4 and 5 correspond to discussion and conclusions, respectively.

#### **2. Materials and Methods**

This section describes the materials used to build the green roof prototypes and the methodology for monitoring and measuring hydraulic and thermal performances. Measurement instruments, constructive characteristics of each green roof prototype, and the rain simulation system are described in detail as well. The dead loads of the green roof systems were determined as the approximate cost per square meter.

Based on the characteristics, amount, and local availability, four materials were selected to develop the drainage layer of green roof systems: (a) basalt gravel (typical material), (b) recycled rubber from tires, (c) recycled polyethylene (PET) bottles, and (d) recycled high density polyethylene (HDPE) trays. In this case, the basalt gravel was considered as a reference material, since it is commonly used as a typical drainage layer of green roofs. The other three materials are conventionally considered waste from other human activities.
