“Visible” Strategies in Duda/Paine LEED Gold Buildings

Green Roofs are often promoted as a new invention, but sod above a structure is an old idea.  On ancient buildings, sod was a useful roofing material because it was easy to install, available regionally and since it was living, did not deteriorate rapidly.  The sod also absorbed rainwater and would hold much of it, slowing its passage into the structure below.

 

On modern buildings, better waterproofing technologies are required than sod can offer, especially in commercial buildings where flat roofs are often incorporated.  Sod on the roof does little to protect against leaks today and its use is not for shedding water as it was before.  So is a green roof a gimmick used only as a demonstrable, popular green building technique? 
 

 A green roof is easily identifiable and signals a different strategy is being employed than buildings in previous few decades, but it also serves an important environmental function.  Urban settings have been documented to be 15 to 20 degrees warmer than outlying spaces because of a dense concentration of dark roofs and paving.  Soil and plant material on a roof avoids a large, dark surface condition and diminishes the potential for warming.





 

Green roof technology takes advantage of another aspect of the old sod roof and that is rainwater absorption and retention.  Without a green roof, smooth roof surfaces allow rapid movement of water toward drains and storm water systems in a large storm event.  With the large percentage of smooth surfaces in an urban setting, rain events can easily create flash flooding conditions as all of the water moves quickly toward the point of discharge.  The force demonstrated with rapid water movement can damage infrastructure as well as erode and alter natural waterways. 

Building a system to handle the worst case conditions would be prohibitive or create waterways similar to the Los Angeles River. 

The goal of recent roof and site design is to slow the discharge of water to roughly equal the rate water leaves a wooded site.  A green roof can reduce rainwater discharge by %. 

By David Davis