In San Francisco, you must obtain a permit from the Department of Building Inspection (DBI) before undertaking any significant plumbing, mechanical, electrical or construction work. If you don't think that your particular project warrants a permit, you should still do some research to make certain. It's better to err on the side of caution, as San Francisco takes permit enforcement seriously. The Web site for the DBI offers a comprehensive guide called How to Obtain a Permit for 1 & 2 Family Dwellings which provides an excellent overview of the permit process, including information on which types of work require a licensed professional and which types are exempt from permit. You should review this document carefully before going ahead with any alterations or upgrades to your home. 

Depending on the nature of your project, your permit application may also require review by the San Francisco Planning Department which examines proposed work in the context of city and neighborhood planning. For details, stop by their Information Counter at 1650 Mission Street, Suite 400, San Francisco or call (415) 558-6378. You can also visit the Planning Department online for more information.

Realize that you must obtain separate permits for each type of work involved in your project: electrical, building, mechanical or plumbing. More elaborate jobs, such as the addition of a new bathroom, might even require all four. You or your licensed designee must submit the permit application in person, but you may call the DBI at (415) 558-6088 to have certain applications mailed to you ahead of time.