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What’s the deal with Granny Flats?

We’ve been asked more and more lately about Granny Flats, also known as Accessory Dwelling Units;

What are they, how did they exist, and can I build one on my property? 

Accessory Dwelling Units (ADU) are a secondary small dwelling right on the same grounds (or attached to) your regular single-family house, such as: an apartment over the garage, a tiny house (on a foundation) in the backyard or a basement apartment. With the housing shortage across the Bay Area, many cities are loosening their regulations for these units, making it easier than ever to create one!
There are certain requirements you must meet to obtain a permit to build an ADU (a.k.a, granny flat). Here you can read about them more in depth, but I’ll note you the basics for San Jose:
  • To construct a secondary dwelling unit, your property’s lot size must be a minimum of 3,000 square feet in total.
    • ADU must be at least 600 square feet if your lot size is 3,000-5,444 square feet
    • ADU must be at least 700 square feet if your lot size is 5,445-9,000 square feet
    • ADU must be at least 800 square feet if your lot size is 9,001-10,000 square feet
    • ADU must be at least 900 square feet if your lot size is 10,001-up
  • ADU cannot be more than 50% of primary dwelling interior square footage (i.e, if home’s interior is 1200 sq ft, the ADU cannot be more than 600 sq ft)
  • ADU must not exceed absorbing 40% or more of yard space if placed in your backyard
  • ADU must include a full kitchen: this means having a sink, food storage, and permanent cooking facilities, like an oven or stove
  • ADU must have a separate bedroom under 400 square feet (if you’re not using a studio layout)
  • No more than one bathroom in the ADU
  • A maximum storage/closet size of 60 square feet
  • On the exterior, ADU must use facade materials that match the primary dwelling unit, including similar roofing, siding, windows, and doors; the architectural form of the unit should match as well, with similar roof pitch and form
  • ADU may or may not be attached to the existing structure
  • Rear and side setbacks can be 5-feet in size.
  • Legally permitted structures, like a garage, do not need to conform to setback regulations. This makes garage conversions ideal for ADUs
  • ADU cannot be built on parcels that already have multi-family properties
  • ADUs are allowed in residential zones R-1, R-2, and R-M
Here is also a link to check if a specific address can be considered for the ADU permit application.
These are just San Jose’s regulations of ADUs, and each municipality has its own standards. If you want to check out the rules for other cities like Mountain View, Palo Alto etc, take a look here. Hope this helps 🙂

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