SPRI and NRCA continue to disagree

On behalf of SPRI and the single-ply roofing industry, I am writing to comment on NRCA Associate Executive Director Mark Graham's article "ANSI/SPRI RP-14," September 2010 issue, page 24.

I would like to address each concern Graham voices in the article.

Growth media size: There is no gradation of growth media. There are no requirements for gradation in the RP-14 standard as has been shown by data compiled in the January 2010 study "Wind Uplift of Pre-Vegetated Mats," which was presented to NRCA, as well as by the data NRCA generated. NRCA's small-scale testing demonstrated that with short bursts of 140-mph wind and two-hour tests at 110-mph wind, little or no growth media dislodged from the system in question. The studies show when growth media is fully covered with vegetation, the growth media remains in place.