The U.S. Green Building Council says it is taking concerns about the exclusion of structural materials in the draft of the next version of its LEED green building rating system “very seriously.” Structural engineers are objecting to the absence of structural materials in credits for recycled content, regional materials and renewable materials, renamed bio-based materials in the draft.

“It’s baffling to me,” says Mark Webster, a project manager with structural firm Simpson Gumpertz & Heger Inc., Boston, and chair of the working group on LEED within the sustainability committee of the American Society of Civil Engineers’ Structural Engineering Institute (SEI), Reston, Va. LEED needs incentives to reduce the “significant impacts of structural materials,” Webster adds.

SEI submitted its concerns to USGBC well before the end of the public comment period at midnight Jan. 14. By Jan. 11, USGBC had received some 9,000 comments on the draft, which the group hopes to release as early as 2012.

A LEED life-cycle-assessment (LCA) pilot credit does address structural materials, says Webster. But were the credit adopted, it would provide a more complicated alternate path, he adds.

Webster fears most teams would choose the easier prescriptive path. Those who do may add unneeded finish materials, such as carpets with recycled content, because they can’t easily get credits for the structure. “I don’t know if [USGBC sees] that pitfall,” says Webster.

Scot Horst, LEED senior vice president in the USGBC’s Washington, D.C., office, says the material changes are proposed to address an existing imbalance in LEED, favoring structural over nonstructural materials. The goal is to separate structure from contents in the new version, via the LCA credit for structure. LCA answers the problem of “how to write credits about how less used is more” because LCA is the only way to measure performance of materials, Horst says.

Addressing SEI’s main objection, Horst says the draft will be clarified so that users understand how to address both structural and nonstructural materials, which is critical for new construction.