San Mateo ADU Buildling Resources

California state law dictates a minimum 4-foot setback from the rear and side yard for Accessory Dwelling Units (ADUs). The distance between an ADU and the primary residence isn't set at the state level and may be subject to local regulations.

In California, you can build an Accessory Dwelling Unit (ADU) up to 1,200 square feet, subject to local regulations. However, state law mandates that local jurisdictions must allow ADUs of at least 800 square feet and 16 feet in height.

Generally, you should be able to build an ADU that’s at least one-story and 16 feet in height. Depending on your residential zoning code, you may be able to build two stories

Generally, conversion ADUs and junior ADUs don’t require any parking. Attached and detached ADUs will require 1 parking space, unless your project qualifies for an exemption from the parking requirements.

If you have a single-family home, you can for the most part have one or two ADUs on it. The number of ADUs allowed on multi-family properties depends on the type of ADU constructed and how many dwelling units are already on the property.

The good news is that your property can be any size and be eligible for an ADU. There are no minimum lot size restrictions.

Generally, you can have an ADU on your property if residential uses are allowed on it, although exceptions may apply. Also, you must have an existing or proposed single-family home on your property or an existing multi-family building (which is a fancy way to say a duplex, triplex, or other type of apartment or condo building).

Yes, your ADU can be rented out, although most cities don’t allow short-term rentals of ADUs. This means you can probably only rent your ADU out for a period of month or longer.
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Generally, the property owner will only have to live on the property if a JADU is built on it.

You may be able to build based on how your property is zoned. You’ll need to call your local zoning department to confirm.