Foundations affected by wildfire

I had some questions regarding foundations and if they are affected by wildfires. I strongly recommend having a licensed structural engineer to inspect your affected foundation if you intend to reuse as part of the reconstruction.

Concrete footings and foundations can be significantly impacted by the intense heat generated in wildfires. High temperatures can damage both the concrete matrix and the embedded steel reinforcement (rebar), so it’s critical to thoroughly inspect and assess the integrity of any concrete element that has been exposed to fire.

Inspection and Fracture Behavior
Healthy, undamaged concrete typically fractures through the aggregate itself when subjected to sufficient force. Conversely, in heat-damaged concrete, the paste matrix becomes weaker than the aggregate, causing cracks to form around the aggregate. A practical on-site test is to strike the edge of the concrete with a framing hammer: undamaged concrete will generally be very difficult to break, whereas heat-damaged concrete often crumbles away after a few determined blows.

Strength Reduction
In wildfires such as those that occurred in Colorado in 2012, post-event evaluations frequently revealed compressive strengths of less than 2,000 psi in fire-exposed concrete—representing a 30–50% drop compared to areas shielded from extreme heat. This reduction in strength compromises structural performance and is a strong indicator that reconstruction or replacement may be necessary.

Recommended Actions

Visual Inspection – Look for surface discoloration, cracks, and spalling (chipping or flaking) of concrete.
Hammer Testing – Strike the edges of the concrete; difficulty in breaking may suggest the concrete is intact, while crumbling indicates heat damage.
Professional Assessment – Engage licensed structural engineers or qualified inspectors for a comprehensive review to ensure any rehabilitation or reuse meets current safety standards.

Proper assessment and timely intervention not only ensure the long-term stability of the rebuilt structure but also protect the safety of its occupants. If in doubt, always consult with professionals who can guide you toward the most appropriate course of action.

Happy to refer qualified structural engineers for assessment.

Stay safe, everyone.
reach out at Sam@studionorthla.com or ‪(323) 985-4643‬ for any questions.