THE IMPACT OF GREEN ROOFS IN URBAN HEAT ISLAND EFFECT

Presented by:Abdul rashid p

Reg no:14180162

INTRODUCTION

According to the Population Reference Bureau, in 2010 50% of the world population is settled in urban areas

Excessive and unplanned growth of urbanization has caused undesired side effects around the world.

Urban Heat Island (UHI) as a consequence of urbanization

Roof surfaces are key interfaces in the volumetric exchange of energy - constitute a large fraction of urban surface areas - due to their exposure receive considerable solar radiation

Therefore it important to understand heat storage capacities

URBAN HEAT ISLAND EFFECT

•The urban heat island effect is the temperature increase in urban areas compared that with surrounding rural areas

• Impact on energy demands, air quality and public health

FACTORS THAT CONTRIBUTE TO THE RELATIVE WARMTH OF CITIES:

Due to less vegetation

Runoff is greater in the cities - pavements are largely nonporous, thus evaporative cooling is less

Waste heat from city buildings, cars and trains

The thermal properties of buildings add heat to the air by conduction

Elevated temperature from urban heat islands, particularly during the summer, can affect a community's environment and quality of life

IMPACTS:Increased energy consumptionElevated emissions of air pollutants and greenhouse gasesCompromised human health and comfortImpaired water quality

WHY DO WE CARE ABOUT UHI?

A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane.

Include additional drainage and irrigation systems.

WHAT IS A GREEN ROOF?

What do they look like?

Green roof block

USES OF GREEN ROOFS:oReduce heatingoReduce storm water run offoNatural Habitat CreationoFilter pollutants and carbon dioxide out of the air. oAesthetic improvementoHelp to insulate a building for sound.oIncrease agricultural space.

 

HISTORY

•Green Roofs have a centuries-long history.

•Developed in Germany in the 1960s, and has since spread to many countries•Early Mesopotamians, Greeks, Romans, and Persians used them to green and cool brutally hot landscapes• The Hanging Gardens of Babylon were the most famous green roofs

COMPONENTS OF A GREEN ROOF

The components generally include the following layers:

• Waterproofing / root barrier layer.• Drainage / water storage layer.• Filter layer.• Planting medium.• Vegetation.

WATERPROOFING

•Waterproofing layer Bitumen-TPO-EPDM-FRP-Crystalline Active (concrete decks)etc…

•Ideally electronically or flood tested•Will also act as a root barrier - otherwise an additional root barrier layer will be required

DRAINAGE

• Principally managed by a drainage membrane or free- draining aggregate

• Drainage points

• Conduits as appropriate for typical water flow

• SUDS system

FILTER FLEECE

•Used to retain substrate and prevents it from clogging drainage layer

• Filters rainwater and removes fines

• Allows adequate water percolation

SOIL AND SUBSTRATES

• Free draining and lightweight growing substrate. E.g. A mix of sandy loam, peat- free compost and hygroscopic flakes

• Biodiverse roofs: broken concrete, brick, masonry, aggregates etc..from local area

VEGETATION

•intensive roof garden generally uses plants and vegetation associated with landscaping works• extensive garden on the other hand uses very selective types of plants which are dry-resistant or succulent types.

TYPES OF GREEN ROOFS

Classification of Green Roofs can be divided into two main categories – 1.INTENSIVE

• Have a soil depth of one foot or more• Require substantial structural elements to supportthe weight of potential human occupancy andelaborate plantings• Can sustain a wide range of plant species• Typically require a fair amount of regularmaintenance• Often installed as an outdoor amenity space• Can accommodate a wider range of edibles,shrubs, trees

2. EXTENSIVE:

• More common than Intensive Roofs• Shallow, soil is typically 2-4 inches deep• Planted with particularly hardy plants — drought and wind resistant• Lightweight• Low-maintenance• Inaccessible — generally aren’t built for human occupancy• Cover vast majority of roof

Advantages

•Reduces the amount of storm water runoff

• Reduce urban heat island effect

•Increase the life of roof membranes.

•Provide ecosystem services in urban areas

•Increase the amount of urban wildlife.

•Better regulation of building temperatures •Increase fire resistance

• Improve air quality

Disadvantages

• Green roofs initially have a higher cost to build than traditional roofs and high installation cost.

•Require higher maintenance for plant care

• Ongoing maintenance is required

• Green roofs do not work well with very steep slopes. • Retrofitting can be difficult because of weight considerations.

•It is more difficult to locate leaks in the waterproofing material.

How Green Roofs Can Help?

• Two ways to mitigate urban heat island:1. Increase vegetation2. Increase surface reflectivity

• Green roofs do both

• A typical asphalt roof can reach 160°on a summer day while green roofs rarely exceed 80°

GREEN ROOF PRACTICES

•Green Roofs in Chicago

Chicago leads the country in green roofs

CITY HALL

• Among the first of the nation’s green roofs

• Both extensive and intensive plantings

• Contains over 20,000 plants of more than150 species of vines, grasses, shrubs, and2 trees

• Saves the city about $3,600 a year inprojected energy costs

Schwab Rehab Hospital

•rooftop garden added in 2003

•Intensive roof garden

•Built with structure for a 4th story

Ford’s Rouge Center

•In 2004, completed installation of the world’s largest “living roof”

•Installed in pieces like sod

•The new roof stores rainwater and will save Ford money in the long run

GREEN ROOFS IN INDIA

Practice in DelhiA green roof was modeled as the outer layer of the Transport Corporation of India (TCI) office roof.

. The negative heat balance for the green roof during summer confirms that they reduce heat flux through the roof and energy use.

FUTURE POSSIBILITIES

Toyota Green Roofing Tiles:

• 20 inch square tiles that can be installed likecarpet• Their base can connect directly into existingirrigation systems• The tiles are only two inches • Consist of a type of grass from Korea which only requires cutting once each year

Researching the Benefits

Roof Temperature Reduction

CONCLUSION

• With the results in various practices , air temperature can be reduced by green roofs thus it is useful to mitigate urban heat island effect(UHI).

• Due to benefits including energy savings, enhanced roof life, storm water reduction, beautification, and air quality improvement, green roofs make sense for all new roofs

•Eco roofs are one of the few passive techniques that accomplish multiple goals simultaneously.

THANKTHANK YOUYOU