The ember-resistant zone is currently not required by law, but science has proven it to be the most important of all the defensible space zones. This zone includes the area under and around all attached decks and requires the most stringent wildfire fuel reduction. The ember-resistant zone is designed to keep fire or embers from igniting materials that can spread the fire to your home.
Click below to view a presentation that goes into more detail. The regulation is still in development, but here's a peek into what considerations may be coming.wkshp-3-valachovic-presentation_ada.pdf