The concern of a vacant lot with tall grass, catching fire and spreading to your home, is shared by some members of our community who have witnessed Wildland fires, or who have moved from areas that have experienced fires.
As we enter summer and our Burn Ban season starts, on July 1st every year, we begin receiving calls about such conditions from alarmed neighbors. While we take fire hazards very seriously, most investigations of these kinds of complaints turn up unsightly lots, weeds that are going to seed, and houses in disrepair, but rarely do we find a true fire hazard.
When Is It a Hazard? When Is It Not a Hazard?
A "defensible space" of at least 30 feet is generally adequate to protect a structure. This includes removing lower branches, and landscaping with appropriate, low growing vegetation. (See illustration, taken from the Washington State Department of Natural Resources (DNR) Website Presentation (PDF) on the Wildland Urban Interface). Your own "lean, clean, green" spaces around your house, and your otherwise tidy neighborhood, may be all the protection you need from your neighbor's tall grass. For instance, if the lawn is green from the property line back to the neighbors shed or garage, that space is counted toward a defensible space.
Even where a true fire hazard exists, all that may be needed is a mowed perimeter of the lot where the tall grass exists. For example, if your lot already has a twenty-foot Lean Clean and Green Zone, mowing a ten-foot swath of the neighbor's tall grass would be all that is needed to form this 30-foot defensible space.