There are two main resources for research you can easily get access to: The City and County Building Departments have microfiche documents that you can review to find out more about the property in question.
For instance, at the City of San Diego Building Department, they have a Records Office on the second floor where you can go and do your own research. You have to make an appointment first, so someone can guide you on what you need to do to get the information you are looking for but once you get in, there is a lot you can find out about a property, parcel, neighborhood or even subdivision. They have maps for zoning, sewer and many other disciplines. They have documentation on the different developments in the city, and most important, they give you access to all those documents and even let you make copies of some documents if you follow their guidelines.
For almost every property in San Diego, if they have a site plan, they will let you make a copy of it. If the project was developed or designed by a specific person: architect, designer, contractor and they have a name on record, you would need written permission from that person to be able to get copies of the drawings from the City when they have them. Sometimes the projects are so old, the people in charge are people who have already passed away which makes that impossible but that is the way the city handles that.
The City only has information from 1955 till today if there is any on the property you are researching. Usually you can make copies of the permits filed on the property such as electric, plumbing, etc. which is very helpful when it comes to finding out how recently the property was upgraded.
At the San Diego County Offices they also have a Records Office where you can do research but if you want copies of the Building Records for instance, which is a document you need for submitting plans at the City, you need a letter of permission from the owner to be able to get it. When I start a project, I always request a letter from the homeowners the day we sign the agreement. On that letter they authorize me to get all the information from the City and County Records Office necessary to develop the project. That way I can start doing my research right away.
The Building Records document is usually a two page document which shows the first date when the property was appraised. Usually, if the property is very old, they only show what was there the first time the owner paid taxes on the property. This document shows general information on the property such as: square footage, number of rooms, materials, permits acquired, etc. Every time you submit plans to the City you need to have this document in the package as part of the documentation required for the construction permit.