Q. We are bidding on a large school project that is planned to be a LEED-certified structure. The architect has asked if we can supply a concrete masonry unit (CMU) that could be cast with supplementary materials to help qualify for LEED points. Are there any guidelines?
A Making a CMU that conforms to the U.S. Green Building Council's rating system is not difficult, but it requires an approach that is more than adding a supplementary cement to the recipe. The architect is required to look at the total structure, not just a key element.
The National Concrete Masonry Association (NCMA) has just published new guidelines for green (sustainable) CMUs. The document reminds producers that earning the LEED recycled content credit is based on the recycled content percentages, on the total value of all permanently installed materials on the project. These calculations exclude mechanical, electrical, and plumbing components, along with specialty items such as elevators.
Masonry's contribution to the percentages of recycled content is added to the contribution from other building components. The recycled percentages are based on both weight and cost. As a producer, you must report to the design team the percentages of both pre-consumer and post-consumer recycled content. NCMA has developed a simple spreadsheet a producer can use to calculate these percentages. This table covers both concrete masonry building and hardscape products.
The green road must be traveled carefully. When a concrete masonry product mix-design incorporates recycled materials, provide proper testing to ensure that using these materials does not adversely affect the quality or safety of the units or construction.
NCMA's document, TEK 6-6A, “Determining the Recycled Content of Concrete Masonry Products,” provides guidelines for calculating recycled percentages to report to the design team, what can be counted as recycled content toward accumulating LEED points and other sustainability credits, and how you can achieve credit with leftover units from a jobsite.
The engineers who developed the paper also included a discussion on determining the fire rating of units produced with unconventional recycled products.