Building reuse plus addition

I have the same question, if someone has any information, would be great! thanks. 

Hi Erica - Great question.  My understanding is it depends on whether you're pursuing Option 1/Path 1 or Option 1/Path 2.

For Path 1, my instinct here is to compare to how similar calculations were done under v4.  In v4, the BD+C Reference Guide includes sample calculations for Option 3, which is similarly unclear in its descriptive wording around whether the denominator should be the

• full eligible existing building area or
• the total built building area (existing + new).

However, the Futher Explanation-Calculations section of the Reference Guide clears things up.  The sample calculations clearly show that the denominator should be only the existing building area eligible for reuse - i.e., without additions.  Similarly for v4.1 Option 1/Path 1, the intent of this path closely matches that of v4 Option 3 (although removes non-structural elements from calculation).  For this reason, and from the v4.1 credit language "Calculate reuse of the existing project area according to Table 1" - my understanding is that the denominator, as noted above, should be the existing building area.  

By contrast, Path 2 requires the denominator to include the total building, both existing and addition, in the denominator.

In the old LEED 2009 version of the building reuse credit, there was a limitation on how big the addition could be relative to the existing building reuse in order to use what is now Option 1 under LEEDv4.1. Has anyone run into anything about using Option 1 vs. Option 2 given the relative size of the existing building to be reused and the new addition being proposed?