Exempt compounds

The credit language references the VOC limits from the 1993 edition of GS-11 for interior and exterior wall paints. That edition requires use of USEPA’s Method 24 which would involve testing followed by backing out water and exempt solvent content by calculation. Technically, ASTM 6886 is more accurate for low VOC and/or high water content coatings; however, it is not the cited method. For other types of coatings, the credit language cites SCAQMD Rule 1113 as it existed on January 1, 2004. Technically, any coating that complies with the limits in the LEED IEQc4.2 addenda Table 1 should contribute to the credit.

Rule 1113 includes two equations for calculation of VOC content. All categories besides Low Solids Coatings are calculated less water and exempt solvents. The Low Solids category is calculated including water and exempt solvents. As a practical matter, the majority of coatings manufacturers use calculation as the legal means to comply with Rule 1113.
Rule 1113 also allows for direct testing of VOC content via a modified version of USEPA Method 24. This would generally provide defensible results for a manufacturer – although the same holds true for accurate calculations. SCAQMD is also known to use a modified version of ASTM 6886 in their laboratory for enforcement purposes.

Rule 1113 was created with the intent of eliminating ozone precursors and therefore exempts a limited range of VOCs that do not participate in ozone formation. The exempt list is based on USEPA definitions and lists as adopted and modified by both the State of California and the South Coast Air Quality Management District. The exempt list looks extensive, however, from a practical perspective there are only five VOCs and a family of silicone oils that have formulary utility. I have a personal bias against two toxic exempt compounds, methylene chloride and perchloroethlyene, that I encourage specifiers to avoid.

From a practical perspective I’d say stick with the Rule 1113 approach as it is consistent with the 1993 GS-11 standard. Ask the manufacturer if exempt compounds are used in the product if you or your client wants to know. Also be aware that the less water/exempt compound calculation can yield a VOC content number that can be dramatically higher than the actual VOC formulary percentage. This is particularly relevant for mid-range solids products.

Paola, why are you doing these calculations? Are you a manufacturer / testing agency? I'm not sure a designer or architect can do the level of calculations that Dwyane outlined.

Dwayne, thanks for the detailed response. I would like to hear more aobut those two compounds. Have you been over the pilot credit 11 discussion?