Green Roofs: Environmental Benefits and Urban Potential

Project Name: The Sustainable City.
Location: Dubai, United Arab Emirates ( $UAE$ ).
Primary Goal: To achieve a Net Zero Energy development and serve as a model for future energy and transport solutions.
Key Principles: - Reduction of energy intensity through design. - Integration of social, economic, and environmental sustainability. - "Future Ready" approach: preparing for climate change and reducing human footprints by involving the community.

Villa Orientation: All villas are designed to be north-orienting. - Purpose: To maximize shade and avoid direct sunlight. - Economic Impact: Significantly reduces air conditioning costs and subsequent carbon emissions.
Roof and Building Envelope: - UV Reflective Paint: Used on exteriors to deflect sunlight and reduce thermal heat gain. - Thermal Performance: Windows and roofs are engineered with high thermal values to maintain internal temperatures.
Architectural Integration: Solar panels are not treated as unsightly additions but are integrated into the architecture of the roofs and parking structures.

Stream Separation: The city separates incoming water into two distinct streams: Black Water and Gray Water.
Gray Water Treatment: - Sources include washbasins, showers, and washing machines. - Treatment occurs on-site within the community in an underground plant to avoid odors and aesthetic issues ( $0$ odors reported). - Storage and Use: Treated gray water is stored in lakes/ponds and pumped through the farm to irrigate the landscape.
Passive Biofiltration: - The city utilizes "Biofilters" such as Papyrus plants (traditionally used in Egypt for paper). - These plants are soaked in the water to provide nutrient uptake, improving water quality further as it moves through the system.
Cooling Applications: Treated gray water is used to keep cooling pads moist in the biodomes.
Sewage Effluent: Other landscaping is irrigated using treated sewage affluent.

Grid Connectivity: The city is grid-connected, allowing it to feed solar energy into the main grid and tap back into it as needed.
Capacity and Scale: - Total Goal: $10\,MWp$ (Megawatt Peak) installed capacity. - Total Panels: Approximately $40,000$ Photovoltaic ( $PV$ ) panels targeted. - Current Progress: $26,000$ panels installed at the time of filming. - Daily Production: The system can produce $10\,MWh$ (Megawatt hours) of solar energy per day.
Solar Car Parks: - $3\,MW$ of the total energy capacity comes from solar panels installed on car park shading. - This energy specifically powers city services, including the cooling pads, farm operations, street lights, and water features.
Maintenance: Panels are dry-cleaned to maintain efficiency.

Service and Maintenance Fees: Residents (both owners and tenants) pay $0$ service fees and $0$ maintenance fees.
Revenue Model: - The city includes a "Mixed Use" area (The Plaza) at the entrance with $15,000\,m^2$ of rental space. - This space is only for rent, generating revenue for the developer. - A portion of this rental income is used to offset all community costs: street sweeping, panel cleaning, landscaping, security, and mosque maintenance.
Property Ownership: Property is available as "Freehold," allowing for both purchase and rental options.
Community Spaces: Residential clusters are completely car-free, providing safe, communal spaces for children and social interaction.

Urban Farming: A farm runs the entire length of the city.
Productive Landscaping: The city balances amenity and utility. Trees include: - Date Palms: Pollinated in spring and harvested in August. - Fruit Trees: Avocado, papaya, pomegranate, mulberry, and fig trees (scattered to benefit from the palm shade).
Community Gardening: Residents manage farming areas for approximately $6$ months of the year during cooler climates.
Biodomes: The city contains $11$ biodomes for food production. - Crops: Experimentation with $40$ types of herbs and vegetables including leek, parsley, mint, basil, chicory, spinach, coriander, cherry tomatoes, and lettuce.
Passive Cooling System (Fan and Pad): - A "Desert Technology" used for over $40$ years. - Mechanism: Large fans blow air out, creating negative pressure that pulls air in through corrugated cardboard pads. - Cooling Effect: Pads are kept moist with treated gray water. Evaporative cooling can drop temperatures from $45\,^{\circ}C$ to approximately $30\,^{\circ}C$ . - Energy: The fans are powered by solar energy from the car parks.

Comparative Statistics: - Global Average Carbon Emission: $\approx 7$ metric tons of $CO_2$ per person per year. - Sustainable City Average: $\approx 3$ to $3.1$ metric tons of $CO_2$ per person per year. - This figure includes the impact of residents commuting outside the city.
Waste Management: Recycling stations are distributed throughout the city at a ratio of $9$ stations for every $90$ villas.
Circular Economy: Construction waste from "Phase 1" (such as wood pallets) was repurposed to create community furniture, including benches, picnic tables, and large decorative chairs.

Internal Mobility: The city is designed for electric buggies, bicycles, and jogging tracks. Cars are restricted to the periphery (solar car parks).
Electric Vehicle (EV) Incentives: - Direct provision of charging stations. - Cash Subsidy: As part of the sales contract, villa owners receive an incentive of up to $\in 10,000$ (approximately $40,000\,AED$ ) toward the purchase of their first Electric Vehicle.

Robert Llewellyn: Asked about the temperature difference between seasons. - Response: In January, it is $25\,^{\circ}C$ , but in mid-summer (June-September), it reaches $45\,^{\circ}C$ with high humidity. The design accounts for this by providing outdoor usability for $8$ months of the year.
Robert Llewellyn: Noted the community pool as a contentious point in sustainability. - Response: The pool is a closed system that is filtered and only topped up to replace evaporation. It uses an environmentally friendly treatment system and is essential for social sustainability in the Middle East climate.
Robert Llewellyn: Inquired about the public perception of the project. - Response: Initially, there was significant skepticism from bankers and the public (post-financial crisis). However, the completion of Phase 1 demonstrated that sustainable development is not more expensive if planned correctly from the start. "An afterthought is expensive," but integrated technology is economically viable.