With the steep elevation on often rocky soil up there, septic permitting and construction can be a beast.

Yes permits expire (as Greg mentioned) in Baltimore City. 2.)

Yes, you need a permit from the city to put a pool in.

As long as you have a letter from a ISA certified arborist that states the tree is unsafe, you can remove the tree without a permit. 

Raleigh, OTOH, makes it difficult to add units on to existing houses, even when zoning would permit additional units, and makes it nearly impossible to build ADUs.

The owners (man and wife in their 70’s) say the 2nd Unit (1bd/1ba) was built with permits for their daughter decades ago but was not recorded because owners did not want to pay additional property tax on the build.  

CEA is not permitted to file for bankruptcy protection, and I believe if they get an excess of claims they prorate payments.

However, after reading about permits in J Scott's "Estimating Rehab Costs" book,  I learned that some jurisdictions don't allow rental property owners to pull their own permits.

It could take you many months to even pull permits and a savvy HML will know this.

While I do flip homes this is one if permitted to have 4 units with 4 bedrooms would be something I would hold on to as an investment.