This paper describes the California Simulation Engine (CSE), a public domain, multi-zone, short-time step, detailed annual building simulation application developed to support the 2013 California Title 24 residential energy standards. CSE implements state-of-the-art algorithms including an MRT-based zone representation, a coupled airflow network, and simple HVAC models. In addition to summarizing CSE modeling methods, the paper presents a preliminary comparison of simulation results to data measured under the Central Valley Research Home project currently underway in California.