Great resource, and as an ex-Clevelander, I generally agree with the color codes.

Fire code prohibits air vents shared between multiple units in multifamily.

.#1 - Do not panic and alter existing investments. 

Going to read the code a bit more thorough to see if I can make it work legally.

Data sources are from Zillow.com/data, US Census Population growth, and ZIP code data sources (example within tabs). 

Because of building codes that we didn't know about, we were un-able to get permitting to build a new garage or carport.

You can do that yourself to some extent (check zip code, age of home, look at finishes, etc.), but for example, my Realtor will say, "Here's what I found on properties that were within .5 miles of yours, similar age and sq. footage, and rented out in the last 30 days..."

Un-permitted work is often of no value, or of lesser value because there is no official inspection saying the work was done up to code.  

Regarding the legalities of if STR's are allowed in the municipality you would be need to check with the local codes office to confirm.  

There are there rent increase stipulations in Philadelphia code now?