Share 'High-rise Residential - Favored retrofit strategies & stories'

For those conducting energy audits and developing retrofit work scopes for high-rise apartments, please share your experiences in this thread.  Successful methods, pitfalls and complete disasters are all fair game for sharing with the group.   Since there are distinct difference between high-rise and low-rise strategies, let's keep our discussion here only on high-rise. Low-rise thread stories go…