I always believe that information is the key in real estate, nothing is wrong in finding out the truth about a property, especially if it is already public information. Any problem can be fixed and dealt with if the facts are out on the table. In addition, properties that are in order, well maintained and have permits should reasonably receive more value and those that are not, less. First, of course, talk to you neighbor if at all possible and try and resolve your concern amicably.
Since the Granada Hills motto is "The Valley's Most Neighborly Town", I would only even consider taking action if the suspected structure actually would cause a marked decline in your property values and/or diminishes your quality of life and privacy. It may well be a "Granny flat" (640 sf max living space without a kitchen) made legal a couple year's ago by SB 1818. Enough babble...
- better to go in person to see all they have on file (takes about an hour), you can also fax.
BUILDING ACTIVITY: http://www.permitla.org/ipar/index.cfm - this is a great site to see recent building activity.... "The purpose of the Internet based Property Activity Report is to allow easy access and visual display of general information from the Los Angeles Department of Building and Safety (LADBS) Plan Check and Inspection System (PCIS) and the Code Enforcement Information System (CEIS)..."
ZONING: You better check this out ... www.HowsRealEstate.com (my new website, not very polished yet)...but..it as links to the current and proposed zoning changes for all of Granada Hills - they are being reviewed now. The L.A. Planning Department's head, Gail Goldberg, recently stated that the revision of the GH's Community Plan should be finish this year.
You might want to get preliminary advice from: (1) your Neighborhood Council www.ghnnc.org if you live north of the 118 frwy, or www.ghsnc.org if your home is south of the 118 - they are aware of the changes and knowlegable, (2) a local homeowner or resident's group in you area, (3) the L.A. City District 12 Council Office: www.cd12.org....otherwise, I would strongly suggest an attorney specializing in real estate and land use if you want to pursue only after fininding out the facts.
P.S. If you haven't gotten it by now, the History of Granada Hills picture book was published a couple years ago by Jim Hier...it's a great read!