San Mateo, CA, Guest House Planning and Building Permits – Accessory Structure vs. Accessory Dwelling

San Mateo turns out to be a tricky city to build an accessory dwelling but quite typical for permitting the most common types of projects: additions, remodels, or accessory structures.

Accessory Dwellings are a very specific type of new home.  The “dwelling” word is a huge trigger for additional permitting requirements.   The definition of an accessory dwelling is determined by the number of plumbing fixtures, and the inclusion of a kitchen and a full bath.   A water heater counts as a “fixture”, as does a sink, toiler, shower, etc…

For homeowners in the preliminary scoping or idea phase it’s probably best to consider an accessory dwelling as one category while lumping all other potential project types into a second category.

In our research and permitting of two projects in San Mateo we’ve learned a few lessons that we’ll list below.  Keep in mind the planning/zoning rules change almost constantly and they are interpreted differently for different sites.  So this may be a helpful start but you have to talk to the planning department to figure out what you will do on your own project.

The first project involved converting a collapsing garage nicknamed the “rat house” to something cute that could serve as a guest room for parents who visit from Los Angeles, an office for mom, and a space for her daughter to do arts, crafts and practice her instruments.

The home was the type of home that you find in many of the older neighborhoods across California with a 5,000 square foot lot and a three bedroom two bath home.   There are two main hurdles that we found right off the bat were:

Parking: San Mateo required two parking spaces in the rear half of the yard.  Fortunately for this particular project there was an alley behind so that requirement was already met.

Setbacks: The second requirement for significant side setbacks meant a new accessory dwelling would have to go right in the center of the backyard.  This would destroy the backyard and it was an unavoidable requirement so the idea of an accessory dwelling was ruled out entirely.

This left a second plan of an accessory structure:

Parking wasn’t an issue for the accessory structure and setbacks could be 0′.  This allowed for the old one car garage that was along the property line to be demolished and a new guest room/office could be built along the property line. This looked perfect.

The permitting of an accessory structure was still very involved.   The entire process lasted six months and cost $3,045.

Permits were submitted in October and approved in March.

The initial payment was $1,400 and the total Permit Cost$3,045.

In general – with the proper site size an accessory dwelling would be quite manageable.  With a most typical lot (most of the city) an addition, remodel, or accessory structure seems to be the best course of action.

The second project was almost identical, it even had an old structure in the back corner that was converted for the same use – parents, guests, kids, office all in one.  The one change was an addition to the main home for the master suite and a new master bath.  The permitting experience is almost identical when you include the addition, remodel and accessory structure all into one project.

Here’s a snippet of where all the money goes.  You can count the five agencies, in some cities this list grows to 10 or 15 agencies.   (Fire, building, planning, park, archives, taxes)

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1 thought on “San Mateo, CA, Guest House Planning and Building Permits – Accessory Structure vs. Accessory Dwelling”

  1. What is the max size or sq ft for an accessory building i.e. Work shop , garage. I have an 8,800 sq ft corner lot in the Shoreview area of San Mateo

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