Why major hail storms commonly turn out to be more wind than hail. by Lewis O’leary

In researching the Weather Data for the June 14, 2017 hail storm in the Midland/Odessa Area, I shocked a veteran contractor that worked in storm clean up by telling him that I’m finding that the little noticed “wind element” of storms was likely the most damaging element, as opposed to the hail that almost everyone was focusing on.

Many professionals that are involved in assessing damages from a “hail” storm subscribe to “hail reports”. However, in many cases, it is important to remember that nearly all “hail” storms are in reality a “wind & hail event.   In this case, the National Weather Service Data provides compelling evidence of wind speeds in the range of 70 – 78 mph, with one report of 100 mph in the Odessa area. Most storm chasing professionals know that the prevailing wind rating for buildings is at least 90 mph. This would suggest to most if they don’t see a roof peeled back, or holes created by large hail strikes, there isn’t much worth further attention. This is exactly the opposite of the truth when dealing with a building or roof that was built to a much earlier wind code. These older but still very serviceable roofs will commonly develop “latent” damages at about half of the uplift force needed to do the same damages to a current code compliant roof. Examples of this are cited throughout the Enhanced Fujita Scale. For example,

Older metal buildings are projected to begin to reach the “Threshold of visible damages” at or about 54 mph, whereas newer metal buildings are projected to begin at 83 mph. Using the formula of Force equals Mass times Velocity squared (F = MV2), 83 mph winds pack over double the force that would be experienced at 54 mph.

In the case of some commercial flat roofs, the older, but still very serviceable, roofs are projected to begin to reach the same threshold for visible damages at or around 55 mph. Because of topographical considerations, you can get what is called “localized acceleration” considerations, this can be accomplished with a 40 mph “free stream” velocity.

What is not discussed here is that, before you get to a case of damages that rise to “visible to the average laymen” (Degree of Damage, Level 1) you will get to “pre-Degree of Damage, Level 1” damages which would be commonly referred to as “latent” (not readily obvious to a layperson) damages. In the case of an “overlay” (a new roof over an older one), most folks would not know to look beyond the fact that there are no “noticeable” leaks yet. In a like manner, metal building owners may not find “noticeable” leaks yet because the vinyl backed insulation under the roof is likely catching the leaks which have yet risen to significant.

There are many individuals who know how to operate a FLIR camera, followed by a Tramex Moisture Meter and core cut tools. But, if they do not know how to spot “latent” damages they will face an uphill battle of proving that all or most of the leaks are the direct result of a particular event regardless as to whether you are dealing with the hail element or wind & hail.

The bottom line here is that the average contractor, engineer, adjuster, or consultant must learn what the various forms of “latent damages” look like and how to approximate the age of the damage, so that you can make a reasonable case for those damages being the result of the particular storm in question. Such training is in the process of being put together as the “Building Envelope Consultant, Level 4 – Roofs” certification that will be offered by BESI in 2018.