LEED® Stormwater

In this blog we have touched upon changes due to the proposed Virginia stormwater regulations, but often projects have additional standards that must be met, such as LEED®. LEED® is a sustainability standard authored by the US Green Building Council that promotes improved building sustainability in the areas of site impact, water use, energy, materials, and indoor air quality. The newest version of LEED® is scheduled to be implemented in late 2012 and it contains significant changes to the LEED® stormwater standard.

The current version, LEED® 2009, has one credit for quantity control (SSc6.1) and one credit for quality (SSc6.2). Each is worth one point. Version 2012 changes this to a single credit, Rainwater Management, which is worth one to three points. The new credit is based on capture of runoff and retaining it on site through infiltration, evapotranspiration, or reuse. The credit is worth 2 points for the 95th percentile rainfall event or 3 points for (1) the 98th percentile event or (2) the 95th percentile event AND managing onsite the annual increase in runoff volume from the “Pre-Columbian” to the post-developed condition. For this credit, “Pre-Columbian” refers to Christopher Columbus and the period prior to 1492.

The proposed LEED® standards differ from the proposed Virginia regulations in several important ways. The LEED® standard considers the runoff from the 95th and 98th percentile storms which are larger storm events than the 1” event considered by the proposed Virginia regulations for water quality. However, in determining quantity (channel adequacy & flooding) compliance, the proposed Virginia regulations evaluate storm events larger than the 95th of 98th percentile events.

The LEED® standards do not consider the nature of the existing site. The proposed Virginia regulations take the existing land use into consideration. Sites with existing impervious require the proposed runoff volume to be reduced less than for green field sites. Conversely, the proposed Virginia regulations require more runoff reduction volume for projects that do not preserve existing wooded areas.

The relative merits of each system are best left until another day, but my sense is that compliance with the LEED® standards will require significant additional expense beyond compliance with the proposed Virginia regulations. During the design process, the cost of obtaining 2 or 3 points from the stormwater credit will be compared to the cost of other points from credits that produce economic payback, such as energy reduction. However, since most federal projects are required to comply with the Energy and Independence Act, Section 438 standard (EISA 438) standard, which is essentially identical to the LEED®  requirement for the 95th percentile event, federal projects will be handed 2 points.

In conclusion, both LEED® 2012 and proposed Virginia regulations are coming soon. We are all in for a bumpy ride as throw away our old rules of thumb and get used to new ways of thinking about stormwater.

Let me know how you feel about this issue.