Home extended to 3 feet of property line

[Fernando Corrado]

Hello BP,

This weekend I went to an open  house that had a 2100 sq ft. house being listed for 850k.  Yes, I live in Northridge, CA.  

I noticed that the house had an add-on of 500 sq. ft. that they made it to a dining/living space.  The realtor was quick to tell me that it was done "to code" but that it was done with no permits so not listed in the total square footage.

When I went outside, I noticed that the add-on outer wall was 3 feet from the property fence on the side of the home.  I believe in California it's supposed to be 5 feet?   I mentioned it to the realtor and she kind of brushed it off and started talking about the great upgrated kitchen worth 100k and other improvements to the house.

Is this something that should be reported to someone or as a nosy neighbor just going to an open house, I should not be concerned?