City Council members are generally pretty tight-fisted stewards of taxpayer dollars. So the council’s 8-1 decision last week to allocate $341,000 for a new roof — this time, a green roof — for the city hall annex that houses the council’s public meetings and offices raised some eyebrows.
In fact, the decision should be applauded. It’s far more cost-efficient over the 50-plus year life of the green roof than conventional roofs. More to the point, it also shines a light on just one of the water detention systems that are expected to save the city many millions of dollars — probably hundreds of millions — over coming decades as the city shifts from a combined sewer system to a system that diverts massive amounts of storm-water-runoff out of the sewers and into better use in myriad other ways.
Putting up a green roof — a roof lined with planters and vegetation that soaks up rain and drains into an on-site detention system rather into the city’s combined sewage — will be three to four times cheaper than a rotation of 15-year conventional roofs over the next 50 to 60 years. On-site storage of rain water also can provide water for the roof’s plants when its dry, and gray-water for sanitary systems.
The math in favor of a green roof is fairly simple. The conventional roof would cost around $100,000 and last about 15 years, and, with a low R-2 insulation, would raise the building’s heating and cooling costs. Over the next 50 to 60 years, sticking with a conventional roof system would cost another $600,000 in constant dollars.
The green roof –minus about $40,000 in life-cycle monitoring and analysis equipment that the city will use to document the roof’s efficiency — would initially cost around $305,000. But it would last more than 50 years, and save 20-to-30 percent in addition on heating and cooling. Indexed against inflation in conventional roof systems and utilities, it would ultimately save the city between $1.2 million to $1.5 million over its life-span, or three-to-four times its upfront costs. Plus, it would help reduce the city’s huge storm-water run-off burden, and that’s perhaps its greater value.