Your first step is to visit your local fire authorities and ask them for the level of "hazard" for your lot and structures. There are different levels of hazard depending on the distance from wildlands or heavy vegetation, the slope of your parcel (or adjacent parcels), the history of damage from previous wildfires, and a number of fire response factors. The effort required to make your residence more fire-safe depends directly on the level of hazard. When you get input from your local fire authorities, ask them to assess your "defensible space," which includes combustibles on your parcel (largely plants) and the space needed for fire equipment should they need to defend your house.
What you may need to do also depends on where your house is relative to the hazard. There are three categories: urban-wildland intermix, urban-wildland interface, and urban. Each has different issues, so let's define them:
Urban-wildland intermix. This would be a house that looks like it was dropped into the wildlands. Most of the hazard from vegetation would be native.
Urban-wildland interface. Lots that are adjacent to areas of wildlands. Many times these are at the perimeter of towns or cities, but can be suburban. Within this category, we can distinguish between "rim" (on the left) and "set-back" (on the right). Rim houses usually bare the brunt of exposure from fires coming up the slope.
Urban. This can also be at the interface if the houses are very close together, such as in a city. The major risk in this case is combustion from an adjoining house. In other words, it could be a domino effect of houses being ignited sequentially.
Losses to wildland fire is a yearly occurrence in California; in the 2003 southern California fires alone, the loss was xx lives and over 4000 structures. The causes of these losses are complex, since they involve the interaction of fire weather, typically in early fall, flammable vegetation both distant and near structures, and the structures themselves. It has been estimated that over 40% of the housing in California is vulnerable to these fires. In many of the areas of the 2003 fires in southern California, two observations were clear: (1) many structures were affected in a random manner and (2) the damage/losses were largely caused by burning brands (embers) from nearby or distant fires. The house that burned in the right background in this photo below fell into both of these categories.
Many homeowners are aware of vegetation management projects in their areas to reduce the spread or intensity of wildfire. However, these programs do not eliminate such fires and cannot assure protection against the type of losses that occur in firestorms. In communities that have wildfire regulations for new construction, few have any restrictions that make older houses more fire-safe. Therefore, the homeowner is the key to reducing these losses.
The randomness of failure relates to several factors: the probability of ignition of a vulnerable portion of a particular structure, design of the structure, location and character of ancillary structures, aspect and location of the structure relative to the direction of the firestorm, characteristics of the firestorm, and parcel/community slope and vegetation characteristics. The end result is that many structures are destroyed/damaged in patterns or manners that are not predictable. It is not unusual to find a single damaged structure among undamaged structures or a single survivor in a group of lost structures.
The ember hazard is very difficult to predict since the source and travel distance of the embers is highly variable. The initial wildfire siege is typically by embers; this may be followed by radiation or flame impingement exposure (probably a few minutes) and embers during and after the flame front. A number of wildfires have been characterized as "ember storms," literally raining embers on structures. To appreciate the number of embers that might land in one of these storms, look at the trampoline in these photos. The first shows that is was overturned to keep it from blowing away; next is when it was tipped up after the fire to see the holes burned in it!
