Book Title: Green Roofs
Author: Dr. Mahnaz Mahmoudi Zarandi

Green roofs are designed to transform inactive rooftop spaces into dynamic environments. Although considered private or semi-public areas, they play a significant role in enhancing urban ecological efficiency and improving the quality of urban life. The impact of green roofs at the city level is considerable. Transforming house roofs into green spaces improves air exchange between densely built-up areas and open spaces, moderating urban air humidity.

Benefits of green roofs include:

• Providing green spaces for building residents and city dwellers.
• Reducing heat exchange between the building roof and the external environment.
• Decreasing energy consumption in buildings.
• Reducing carbon emissions and dust, while increasing oxygen and humidity levels.
• Capturing rainwater and reducing sewage flow, alongside producing flowers, plants, fruits, and vegetables.
• Creating jobs, enriching leisure time, and offering open spaces with beautiful vistas.

Green roofs constitute approximately 25-40% of urban surfaces. Transforming these roofs into green ones offers numerous benefits, including reducing air pollution—a major problem in Tehran and other large cities in Iran—since plants can break down organic compounds and absorb and decompose gaseous pollutants.

Considering the significant impact of air pollution on the health of citizens, various cities in America, Europe, and even Dubai have long promoted the expansion of green roofs through cultural development and by providing incentives for builders, executing organizations, and users.

Chapter One: Overview of Green Roofs

This chapter documents the goals of sustainable design achieved through green roofs. It includes past research and examines different types of green roofs, comparing their quantitative and qualitative differences to conventional roofs. The heat transfer process in planted roofs is entirely distinct. Due to their biological functions such as photosynthesis, transpiration, respiration, and evaporation, plants absorb significant amounts of solar radiation. The remaining solar radiation converts into heat load, affecting the indoor air conditions as it passes through the building's roof elements.

The types of green roofs—extensive, semi-extensive, and intensive—are reviewed for their structural features, soil layer depth, types of plants, and maintenance practices.

Challenges associated with green roofs are also addressed, along with solutions for potential problems. Using global experiences, the book outlines the primary prerequisites for developing green roofs in Iran.

The chapter also discusses the components and details of green roofs. The components of green roofs and roof gardens are identical, but they differ in the depth of the components and the project design application. Each manufacturing institution or commercial company categorizes installable components based on its unique approach and market competition. Each component of a green roof has specific functions and together they form an integrated green roof system, including: vegetation cover, growth medium, filter layer, erosion control, water protection, drainage layer, protective layer, root barrier, waterproof layer, thermal insulation, vapor barrier, and roof structure.

Features of each component are described, and introducing examples of these layers can help the reader design new types of green roofs.

Chapter Two: Green Roof Standards

This chapter addresses the performance standards for components of green roofs including vegetation, soil, drainage, irrigation, insulation, root barriers, and roofing membranes. It specifically highlights the LEED (Leadership in Energy and Environmental Design) standards relevant to green roofs. LEED certification, recognized as the national standard in the United States for evaluating green buildings, is also globally accepted as a benchmark for designing, constructing, and operating buildings that claim environmental performance. Initiated in 2000 by the U.S. Green Building Council, LEED certification can be applied to any building type and size. This certification influences designers' perspectives on successfully implementing green roofs and provides them with knowledge in this field. Buildings with green roofs must comply with these defined standards, which assess the building in terms of safety, quality, materials, etc.

The five main criteria of LEED certification are:

1. Site Sustainability
2. Water Efficiency
3. Energy and Atmosphere
4. Materials and Resources
5. Indoor Environmental Quality

Each of these criteria includes subindices that are discussed in this chapter concerning green roofs.

Chapter Three: Suitable Plants for Green Roofs

Given that each group of plants has specific ecological needs regarding light, temperature, soil, and water, appropriate plants must be selected for green roofs. The basis for plant selection includes:

The plant’s suitability considering its size and shape relative to the limited growth space available.

The growth and adaptability of species to operational and microchemical conditions in Tehran.

Ease of plant maintenance and care.

The chapter introduces four groups of plants: annuals, biennials, hardy perennials, and herbaceous perennials, as well as perennial climbers. Details about the type of soil, orientation for planting, and watering methods for each plant are provided. Fertilization and appropriate types of fertilizers are also discussed.

Chapter Four: Green Roof Implementation Details

Green roofs are designed for long-term use, typically doubling the lifespan compared to conventional roofs. The technology involved in designing green roofs is complex, incorporating non-living variables such as sub-layer depth, weight, composition, drainage layers, and design of the underlying section, as well as living components like plant species mix, materials chemistry, and water access. This chapter presents detailed information on green roofs with various materials used for different layers, including waterproofing materials, roof membranes, protective and moisture insulation materials, drainage materials, root stabilizers, and growth medium characteristics and materials.

Green roofs require diverse design approaches tailored to specific functional objectives, which vary according to geographical locations and customer needs. Detailed knowledge of climatic conditions, slope, irrigation, wind, water and power resources, and maintenance management is also essential and discussed at the end of this chapter.

Chapter Five: Case Studies on Green Roofs

Acknowledging the role of green roofs in expanding green spaces, policymakers have adopted various strategies to encourage their proliferation. Case studies and policy examples from successful green roof projects, particularly in Portland and Chicago, demonstrate effective approaches to cultural development and practical actions for expanding green roofs. The Environmental Protection Agency of Chicago has noted that building green roofs is a viable way to reduce solar reflection, helping to decrease the urban heat island effect and improve air quality.

Due to more stringent environmental policies in the U.S., there are many successful examples of green roof implementations, detailed in the final chapter of the book, including project specifications, designed green roof types, and their operational characteristics.