Green Roofs - Living Architecture Monitor - Fall 2011 - (Page 11)

TABLE 1: COST-BENEFIT ASSUMPTIONS Building size (eight-storey) Roof size Discount rate Green roof risk contingency Investment outlook (years) 100,000-square-feet 12,000-square-feet 4.4% 2.34% 50 years Green roof Installation cost (more than twice black) 1st year annual maintenance Roof replacement premium Roof disposal $287,400 $4,400 33.5% $4,480 $4,420 Black roof $115,900 $700 difficult to quantify for building tenants, though there continues to be more emerging evidence. Neighboring buildings may also achieve approved visibility when comparing a green roof to a black or white roof. REAL ESTATE EFFECT The commercial rents, expenses, vacancy, discount rates and absorption and lease lengths should be identified due to the market value of a green roof. Green buildings realize approximately six percent more rent nationwide, and with green roofs accounting for a significant portion of the green building premium (if this building pursues a green building certification), it is suggested that the green roof carry a potential premium of approximately one to three percent. ROOF LONGEVITY BENEFITS The lifetime of the green roof is significant considering that the lifetime of a well-installed green roof is at least double that of a black or white roof. For a short-term stakeholder, this benefit is minimal, since roof replacement is unlikely in a 10-year timeframe, however, a long-term stakeholder may have to replace their black or white roof twice in 50 years. Therefore, green roofs offer a deferred replacement cost compared to its alternatives. However, it may be necessary to replace a green roof once over a 50-year timeframe, depending on the quality of the membrane. If this is the case a premium should be added to the installation cost to account for the labor needed to remove the medium. Resale is a possibility for many of the components of the green roof. Membranes for all roof types will need to be land-filled or possibly recycled depending on the condition. CASE STUDY – A GREEN ROOF ON A GOVERNMENT BUILDING IN WASHINGTON D.C. Approximately two-thirds of the District of Columbia is owned by the Federal Government. A typical government building was selected to determine the cost-benefit of installing a multi-course extensive green roof compared to a protected membrane roof (PMR) black roof. The cost-benefit analysis included inflation, growth rates for labor and materials, energy, stormwater, community benefits, and diminishing returns based on increases in market supply and experience, a discount rate evaluation and a 50-year timeline. http://www.TheGaiaInstitute.org http://www.TheGaiaInstitute.org

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2011

Green Roofs - Living Architecture Monitor - Fall 2011
Contents
From the Founder
Strata
On the Roof With…
Research
Marketing
Policy: The Game Changer
Policy: Toronto’s Green Roof by-Law
Policy: Energy Code Break-Through
Tools
GRHC: Update
GRHC: Welcome New Members
On Spec

Green Roofs - Living Architecture Monitor - Fall 2011