I think you can simply not apply for the credit, but just look for any spot this should be mentioned when you're documenting MRc2 via LEED Online.The calculation question came up on a library project I'm working on. In our case, it was a renovation, so the entire building is modeled in AutoCAD and it's going to be fairly simple to calculate the volume and/or weight of the existing building (mostly masonry). If the building is not already modeled, creating a simple model may be the simplest approach here.