Challenges of Repairing Wildfire Damaged Hillside Structures in California

In the last several years, hot, dry winds gusting through passes and canyons have driven record-breaking wildfires through the mountainous California terrain, burning and smoke/heat damaging thousands of structures in their wake. The California “fire season” in late autumn follows a warm and dry summer only to be trailed by winter rains. Burnt hillsides offer little resistance to surface runoff, mud, and debris flows, which further strain the earth retaining systems of these hillside structures. Besides thermal damage to structural components, the effects of surface water runoff and even water used during firefighting efforts have a direct impact on the stability of hillside building pads which are frequently crafted on cut-fill lots. Earth retaining systems compromised by unexpected hydrostatic loads and surface runoff sometimes lead to differential settlement of foundations that are already supported on the variable strata of cut-fill lots. Due to governing code requirements for existing buildings, structures with substantial structural damage have to be brought in compliance with current codes and sometimes significantly higher design seismic forces than their original design. This affects the lateral load resisting structural systems including the foundation systems as well. In older structures, the foundation, earth retention systems, and even the fill soil frequently do not comply with current building code requirements. Consequently, reinstatement of fire damaged hillside structures may require extensive retrofit and reconstruction.