Existing Building as LCA Baseline

Kristen,

 I'm sure I won't get them all, but I would expect some of the modifications could be:

- Adjusting for site specific environmental conditions that can affect the structural design (like wind, seismic, and snow loads). Also adjusting for subsurface conditions that can affect the foundation design. The quantity of material in the foundations can vary significantly, even within a few miles, so just being in the same city may or may not ensure a good comparison. Likewise if you are in a high seismic zone the demands can change quickly. Also, I would think that if there is any difference in assumed floor loading that should be addressed to best ensure "functional equivalence". Most of this could be determined by comparing the structural design criteria for both buildings.

- Also, and this is likely obvious, the inputs would need to be scaled to adjust for the GSF difference. There may also need to be consideration for the floor to skin ratio and if that needs to be adjusted to ensure you have "functional equivalence".

-I'm assuming the proposed reference would be in the same climate zone and have the same energy performance, but if not, a rationale for ensuring functional equivalence would need to be developed for the envelope as well.

I suspect these issues, as well as some others are why the USGBC recommended the "Early Design" option as a preferred reference.

Finally, the book at the link below was written by members of the Structural Engineering Institute's Sustainability Committee and has more details on the strategies related to structure.

https://ascelibrary.org/doi/book/10.1061/9780784415054

Dirk

With the caveat that I can't speak on behalf of the LEED team, I will jump in because the text you refer to was drawn from our guide to LCA in green building programs. Please see Appendix B and C in the guide. The short answer is that you may not need to do much at all, other than to scale the material quantities to the different size building. But take a look at the checklists on pp 37-40 to see our recommendations of how to determine whether or not an existing building is appropriate and how to modify as needed.

I posted an answer yesterday - am wondering if it didn't get through.....