Existing building infiltration rates

Not that I know of.

Look at LEED Interpretation #3300, which was updated 7/1/15. It outlines a process for claiming savings from infiltration improvements. It references addendum ag to 90.1-2010. You'll likely need before and after blower door tests to prove it. http://www.usgbc.org/leed-interpretations

Interesting. Thanks for pointing that out Chris. The 2014 update makes sense to me since they reference a specific, whole building baseline. The 2015 update makes no sense at all. It only references the window air leakage, has the project team determine an appropriate baseline, and does not specify any particular testing protocol. You could drive a large truck through those "requirements". In my opinion the 2015 update is a regression, not an advancement. Before and after blower door tests would also be a difficult to defend baseline, especially in this case with the total removal of a facade. IMO the baseline should always be the value required for new construction projects. While there is precedent for existing envelop counting in the baseline all other parameters are the 90.1 minimum value in the baseline including existing HVAC. I think allowing existing conditions for infiltration could open up a large hole for game playing.