A severe storm moves through and the calls start coming in. Roof leaks appear in a warehouse. HVAC units on the roof of an office building aren’t running right. A retail building’s facade has visible damage. For commercial property owners and their insurance carriers, the question is always the same: what did the storm actually do to this building, and what was already wrong before the storm hit? That’s where a forensic engineer’s assessment begins.
Starting on the Outside
A commercial storm damage assessment typically starts with the building’s exterior envelope: the roof, walls, windows, and any rooftop equipment. On a commercial building, the roof is usually the primary concern because it’s the largest surface exposed to wind and hail, and because roof damage on a commercial structure can lead to cascading problems throughout the building.
For flat or low-slope roofs with membrane systems (the kind found on most commercial buildings in the Midwest), our engineers examine the membrane surface for punctures, tears, splits, and displaced seams. Hail impact on a single-ply membrane looks different than hail impact on a built-up roof or a modified bitumen system. On TPO or PVC membranes, hail can create fractures in the sheet that aren’t always visible from the surface but become apparent during a hands-and-knees inspection or core cut. On built-up roofs, hail may fracture the flood coat or displace aggregate, exposing the underlying felts to UV degradation and accelerated weathering.
Rooftop equipment gets the same scrutiny. HVAC condensers, exhaust fans, ductwork, and satellite equipment are all exposed to hail and wind. Dented condenser fins reduce efficiency. Displaced duct connections allow water intrusion. A forensic engineer documents this damage and evaluates whether it rises to the level of requiring repair or replacement, or whether the impact is purely cosmetic and doesn’t affect function.
The Critical Distinction: Storm Damage vs. Pre-Existing Deterioration
This is where the forensic engineering assessment earns its keep. Commercial roofs deteriorate over time. UV exposure, thermal cycling, ponding water, foot traffic, and deferred maintenance all take a toll. When a storm hits a roof that’s already aging, the question becomes: did the storm cause the damage, or did it simply expose conditions that were already failing?
Our engineers look for specific indicators. Storm-caused damage tends to appear in patterns consistent with the storm event. You’ll see hail impacts distributed across exposed surfaces, wind damage concentrated on windward faces or at corners and edges where uplift forces are highest, and water intrusion that began after the storm date. Pre-existing deterioration, by contrast, shows up as gradual membrane shrinkage, chronic flashing failures, biological growth in areas of ponding water, and weathering patterns that predate the storm.
Understanding the difference between storm damage patterns on specific building components, particularly the distinction between tornado-driven damage and straight-line wind effects, is important for both property owners and adjusters. Each type of wind event produces a different signature on the structure.
The engineering report documents both conditions clearly. We don’t pretend that pre-existing deterioration doesn’t exist, and we don’t attribute it to the storm. But we also identify, with specificity, what damage the storm did cause and what repairs are necessary to restore the building to its pre-storm condition. This honest assessment is what makes the engineering report credible to all parties in the claim.
Moving Inside: Water Intrusion and Secondary Damage
Once the exterior assessment is complete, the investigation moves inside. Storm damage to the envelope, whether from hail-punctured roofing, wind-displaced flashing, or broken windows, often leads to water intrusion. And water intrusion in a commercial building can cause damage far beyond the original point of entry.
In a warehouse, water from a compromised roof membrane may damage stored inventory, corrode steel structural members, or saturate insulation that becomes a mold risk. In an office building, water migrating through a ceiling system can damage electrical systems, destroy finish materials, and create hidden moisture conditions in wall cavities that won’t manifest visibly for weeks or months.
Our engineers trace the water path from the point of entry through the building, documenting what was damaged and distinguishing between damage caused by the storm-related intrusion and moisture conditions that existed previously. This is particularly important in older commercial buildings where chronic roof leaks may have caused pre-existing staining, deterioration, or mold growth that predates the storm event.
Structural Connections and Wind Performance
High-wind events, whether straight-line winds or tornadoes, can stress a commercial building’s structural connections in ways that aren’t visible from a cursory inspection. Roof deck fasteners can back out under uplift forces. Bar joist connections at bearing walls can shift. Metal building systems can experience panel displacement or fastener failure at girts and purlins.
For commercial buildings hit by severe wind events, our engineers evaluate the structural connections, not just the surface-level cosmetic damage. A warehouse with a metal roof system might look mostly intact from the ground, but an inspection of the roof deck fasteners may reveal widespread fastener withdrawal that has compromised the roof’s wind resistance for the next storm. Documenting this condition accurately is critical for the property owner’s claim and for the building’s ongoing safety.
The Engineering Report
The deliverable from a commercial storm damage assessment is an engineering report that documents the findings with photographs, measurements, and the engineer’s professional opinion on causation, scope of damage, and recommended repairs. The report is written to be understood by adjusters, attorneys, and building owners, not just other engineers.
A strong report distinguishes between what the storm did, what was already deteriorating before the storm, and what repairs are necessary to restore the building’s weather-tight envelope and structural integrity. It includes a scope of repair that’s specific enough to support accurate estimating and detailed enough to withstand scrutiny from opposing experts if the claim is disputed.
For commercial property owners navigating a storm damage claim, the forensic engineering report is often the document that defines the scope and outcome of the claim. When the assessment is thorough and the conclusions are well-supported, the report gives all parties (the property owner, the carrier, and any involved counsel) a common factual foundation for resolving the claim.
If your commercial property has been through a significant storm event and you’re facing questions about what was damaged, what was pre-existing, or what needs to be repaired, a forensic engineer’s assessment can provide the objective, documented answers that move the process forward.