The goal of this Web-based reference guide is to provide the citizens of Napa County with a comprehensive, yet easy-to-understand source of information on defensible space planning and practices.

The content of this guide is drawn from official fire service documents; national fire prevention associations and councils; and individual knowledge experts within the fire service, vegetation management and related fields.

This reference guide was produced by the Napa Communities Fire Wise Foundation in May of 2009. User comments and suggestions are welcome – please feel free to contact us at

What is defensible space

Defensible space is a law as well as an approach to vegetation management. It includes an understanding of wildfire behavior and contribution of plants to wildfire intensity. It recognizes the risks posed by wildfire to us by our natural surroundings and our vegetation management choices. Another term used in the context of defensible space planning is the “Home Ignition Zone” or HIZ. The HIZ primarily determines a home’s ignition potential based on the proximity to available fuel types within 100 feet or more from a home.

Defensible space is the area around a house/structure and reaching toward an oncoming wildfire. This is an area where the vegetation has been modified to reduce the wildfire threat and to provide an opportunity for firefighters to effectively defend the house/structure. Simply put, defensible space is a zone where vegetation and fire fuels have been modified to reduce or stop fire spread. The goal is to save homes and lives.

The state law governing defensible space can be found on the CAL FIRE Web site at Reference Senate Bill 1595, dated September 2008. 

The Napa County Fire Hazard Abatement Ordinance can be found on the county Web site at:

The City of Napa 2009 Weed Abatement Ordinance and information can be found on the City Web site at:

Why is defensible space important

When you consider that 75% of Napa County’s 500,000 acres is considered a high hazard fire environment, and that over 250,000 acres of Napa County have burned over the past 60 years of recorded fire history, the connection to fire preparedness and survival becomes more obvious. Many areas have burned more than once in the last century. We live in the type of environment that has and will support large, intense, and uncontrollable wildfires.

The good news is that there is a way to live with fire and survive. It’s all about planning and taking responsibility for our personal safety and the safety of our neighbors.

For our discussion, we are breaking up defensible space into four vegetation management zones. Each zone is established at a particular distance and is designed to affect the behavior of a wildfire entering the outermost zone. From wildland to residence, we want to reduce the heat output and burning characteristics of the fuels.

click to enlarge map

click to enlarge map