Yuliia Bortna 10/8/26 Yuliia Bortna 10/8/26

San Mateo ADU Guide (2026): Rules, Fees, and Building a Backyard ADU

San Mateo updated its ADU rules in March 2026: up to three extra units on a single-family lot, no parking, and a building-permit-only process. Here's what you can build and what the city charges.

San Mateo ADU Guide (2026): Rules, Fees, and Building a Backyard ADU

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Here’s the whole process on one page.

Good idea – it’s a family decision.

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