Guest House: AKA Granny Unit, Second Dwelling Unit, In-Law Quarters, Accessory Dwelling Unit, Accessory Living Unit, Companion Unit, In-Law Apartment are all ways of describing a second, self-contained unit with its own kitchen located on a property that is zoned for single family residences.
If you are looking for extra space for a family member or a rental unit for extra income, a detached guest house in your back yard may seem like a great option. However, here in the Silicon Valley every local city has its own regulations regarding whether you are allowed to have this type of structure and specific details as to size, height, for example, if you are allowed to have one.
The rules can be very complex and may even include whether it must be attached or detached from the main house and if the style of the structure must match the style of the original house. One regulation that tends to be the biggest roadblock for any such structure is the issue of parking. Most jurisdictions require at least one extra parking space to be added and some may require more.
For example, if you wish to add a detached unit in the Town of Los Gatos, the unit cannot exceed 900 square feet, be taller than 15 feet at its highest peak, can have up to 2 bedrooms, but you must include 2 extra parking spaces in addition to the 2 minimum required for the main house. None of the parking spaces are allowed in the front yard (the first 25′ from the property line for most parcels).
Even if your property doesn’t qualify for a guest house, you may be allowed to have a detached, habitable, conditioned structure as long as there’s no kitchen. Some cities allow this type of structure to even include a bathroom.
Before getting too in depth with your plans to build a guest house, be sure to visit your local planning department and discuss with a planner your ideas. They will be able to tell you if your property qualifies and can sometimes identify some issues that will need to be addressed while designing your guest house.
Here are a few links to local ordinances: Cupertino, Los Gatos, Redwood City, Santa Clara County, Sunnyvale, Los Altos, Los Altos Hills, Mountain View, Campbell, San Jose, Palo Alto, Menlo Park, Monte Sereno, Saratoga, Santa Clara
UPDATE: A new law goes into effect on January 1, 2017 easing the restrictions on Second Dwelling Units in the State of California in order to ease housing concerns. One new item is making it easier to convert existing space in a home into a self-sustaining unit. For more information: http://sd10.senate.ca.gov/news/2016-09-27-gov-brown-signs-wieckowskis-accessory-dwelling-units-bill-provide-more-affordable