Fast-growing litigation defense firm Tyson & Mendes has purchased a 31,000-square-foot office building in Novato to accommodate its expansion in Northern California.

The San Diego-based firm expects to move its Northern California office from San Rafael to the Class A building at 371 Bel Marin Keys in Novato early next year. Tyson & Mendes now has about 20 lawyers based in the San Francisco Bay Area, roughly twice its size a year ago.