Before adding a room to your house, you should first call the San Francisco Planning Department to confirm that your project is not in violation of the zoning laws for your area. Additions built without clearance from S.F. City Planning could be deemed illegal and ordered removed. If, however, your plans involve creating a new room within the existing dimensions of your home — such as dividing a larger room into a smaller bedroom and a bathroom — you only need to obtain the appropriate permits from the City.   
 
San Francisco is very strict about permit enforcement. Whatever the scope of your planned addition, you will most likely have to obtain a variety of permits –– mechanical, electric, plumbing, etc. –– from the Department of Building Inspection (DBI). Getting permits from the City involves time, fees, and submission of plans, as well as at least one visit from a city building inspector to your home. Bear in mind that your property taxes could also be raised if the addition increases the value of your home. Despite these potential drawbacks, make sure to obtain all required permits before commencing with construction. Failure to obtain a permit could result in bigger problems down the line: anything from the hassle of having to obtain permits retroactively to the DBI requiring you to remove walls or flooring in order for inspectors to confirming the work was done properly.

An experienced contractor, engineer or architect should be aware of San Francisco's permit process. Before moving ahead with any plans, however, you should also take a look at the DBI's comprehensive booklet, How to Obtain a Permit for 1 & 2 Family Dwellings, to educate yourself about the City's permit requirements, particularly if you are going to do the work yourself. Finally, don't forget to consult with a licensed engineer to verify that your plans are seismically sound. Additions, especially ones that create another story or "L" configuration can structurally weaken your home. You should also consult with a professional engineer if existing additions or modifications have not been previously inspected and determined safe.

For more details on zoning, visit the San Francisco Planning Department online or call the Planning Information Counter (PIC) at (415) 558-6377. If you have further questions about permits, call the DBI at (415) 558-0688.

See our Remodeling and Renovating article for more resources on significant home improvement projects.