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The Cost

Installation- Modern eco-roof systems have a maximum weight of approximately 80kg/m2. Existing roof structures, may or may not, require additional reinforcement if they are not rated for this static load. The cost for installing Eco-Roof Systems range between $10. /sq. ft. to as much as $15. /sq. ft., depending on the location and the complexity of the project.

Maintenance Care - Maintenance care of a green roof is absolutely essential. Only with proper care can a green covering be kept intact and able to provide its vital ecological and design functions. The high quality drought and heat resistant plantings used with the Eco-Roof results in a low maintenance costs because the plants largely maintain themselves

Life Cycle Cost Analysis
Comparing three 25,000 sq. ft. roofs in the 31st year of use.
Roof #1 -A Three-Ply, Asphalt BUR roofing system with a price of $9.00 per sq. ft. Average life expectancy 10 years.
Roof #2 -A Modified Hot applied roofing system with a price of $10.00 per sq. ft. Average life expectancy 20 years.
Roof #3 –A Two-Ply Modified Bitumen, Green roofing system with a price of $12.00 per sq. ft.
Average life expectancy 40 years.

    Roof #1

    Roof #2

    Roof#3

    Initial Capital Expense

    $225,000

    $250,000

    $300,000

    Capital Expense/Inflation
    In year 31

    $1,154,595
    (replaced 2x)

    $591,764
    (replaced 1x)

    $300,00
    (original roof)

    Maintenance Costs/ Inflation
    In year 31

    $26,607

    $26,607

    $26,607

    Life Cycle Costs
    In year 31

    $359,682

    $283,939

    $270,447

These calculations take into account inflation and standard tax reduction depreciation.

Additional Life Cycle Benefits

Waste Water or Storm Water Charges - Most municipalities charge for waste/ storm water disposal. The charges are usually based on square footage of sealed areas. Often discounts are offered for the installation of environmentally friendly green roof systems. The effect of the retention capacity of green roofs on public wastewater disposal systems and local authority finances can be extremely positive. Retention and flow delay after rainfall reduces the burden on the increasingly overstressed sewer systems.

Thermal Insulation - A typical eco-roof installation creates a thermal insulation factor, which potentially adds to the overall r-value of any roofing system. The realized benefit varies greatly depending on many factors, therefore, the insulation value of the eco-roof installation should not be considered when determining the overall insulation required.

Repair Cost - The ecological layer provides protection to the waterproofing membrane below.
These roofs typically last twice as long as standard roofs, the life expectancy of waterproofing membrane can be increased to more than 40 years. The increased life expectancy of the roofing membrane is realized because it is better protected from mechanical damage, winds, fire, hail, heavy rains, ultraviolet radiation, foot traffic and extreme temperature differences. Required repairs, when necessary, are performed in a conventional manner with additional care given to protect the integrity of the associated plantings.

Life Span - Current scientific knowledge leads to the conclusion that double the lifespan of a flat roof from 20 to 40 years can be expected.

Intangible Benefits of Green Roofing

Improved quality of Life - Green roofs make a huge contribution to increased satisfaction with life and improved living quality. Employee performance is increased as a result of a pleasant working environment and climate.

Conclusion

The cost-benefit analysis of a green roof demonstrates the value of installing extensive green roofs. An examination merely from the viewpoint of the property owner proves the benefits of roof greening are higher than the costs. When the positive effect on the environment and the eco-system as a whole is taken into account the value is even greater. Additionally, a green roof system will likely provide the added benefits of tax credits or rebates for installation and a reduction in wastewater runoff taxes over the life of the roof. These benefits could substantially reduce the total life cycle cost of a green roof system.


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