Modern research shows that proximity to the nearest structure or house is the strongest predictor of loss in urban wildfires.

The distance between structures and the density of housing in communities significantly impact how fires spread in areas where the wildland and urban environments meet (WUI). In high density neighborhoods during a severe wildfire, extreme burning conditions lead to a higher number of structures to burn. Once a few buildings ignite, a domino effect occurs, with fire spreading rapidly until the extreme burning conditions, usually driven by strong winds, diminish. This type of fire spread in the built environment is associated with costly wildfires in the urban environment.

Defending homes during non-extreme fire conditions is easier when they are closer together, as it requires fewer firefighting resources. However, under extreme wildfire conditions, defending structures becomes harder due to safety concerns for both firefighters and the public. During these conditions, the main way fires spread is through wind-driven flames jumping from building to building. Most buildings are not designed to withstand intense exposure to flames, so once one catches fire, it adds more fuel to the flames, making it even more intense. To prevent this “domino effect”, it is vital to maintain ample space between buildings.