I have an existing bus garage which will be undergoing major renovations in order to become CNG compliant. For the most part, the building envelope (in particular the walls) will not be altered and in its current condition it will not meet the requirements outlined in Section 5. In addition, because of the nature of the construction, an upgrade to the R-value of the walls is extremely difficult and most likely cost prohibitive. A CIR dated 02/20/2009 indicated that if the existing building envelope was untouched, the baseline is as that component exists. However, on 02/28/2011 the CIR was ruled invalid. Must the envelope meet the requirements? Do I have any alternatives?