Hi Phil,
I’m not sure I follow.
Like the Marin County building code, the City of Portland’s thresholds will likely be maximum acceptable GWP/yd3 by strength class. We’ll certainly use EC3 as a reference point, since the tool does a great job of displaying the range of what’s possible in your local market based on published EPDs.
However, since concrete application (foundation vs. PT slab) of the same strength mix changes the potential to reduce GWP, we’ll need to take a broad range of applications in mind when establishing an upper GWP threshold. I don’t think it will be as easy as just choosing the 20th percentile in EC3 (termed “achievable”) and applying that to all mixes within a certain strength class since the policy will cover literally any use of concrete within a strength class.
Please do let me know if I missed a critical feature in EC3 I’ve yet to explore or understand.
Thanks!
Jordan