THE NUTS & BOLTS OF HAIL DAMAGE TO SHINGLE ROOF SYSTEMS
By: Jackie Diaz, APCS, Forensic Scientist, CIERA Services, Inc.
Damage from hail approaches $1 billion in the US each year. Much of the damage inflicted by hail is to crops. Even relatively small hail can shred plants. According to the NOAA National Severe Weather Laboratory, vehicles, roofs, air conditioners, fences, and landscaping are most commonly damaged by hail.
While all types of roofs can be damaged by hail impact, shingled roofs are most susceptible to hail damage. In order for one to properly investigate hail damage as opposed to other causes of damage, a clear understanding of shingle systems must be known. Roof shingles are manufactured in a variety of sizes, shapes and patterns. Composition shingles are comprised of three materials:
During the manufacturing process, these granules are pressed down or embedded into the asphalt coating while the coating is still hot. This layer of granules is referred to as the appliqué layer. Granules comprise about 1/3 of the shingle weight. An average residential roof (25 squares) has 1 ton of granules. Manufacturers take into account that granule loss occurs from the moment that the shingles are manufactured, shipped, and installed. Therefore, during the manufacturing process more granules are placed on the shingles than are needed to cover the mat. Some of the excess granules are not firmly embedded, but instead are loosely held in place on the roofing sheet. Some of the excess granules are often found in the gutters, at the bottom of downspouts, or on the ground after a rain storm. Granule loss occurs throughout the lifetime of the shingle during normal rainstorms and foot traffic. Loss of these excess granules which usually account for approximately 20% to 25% of the total granules on a shingle is common and does not reduce the weatherproofing life of the shingle. Granule loss only becomes a concern for shingle water tight integrity and performance when bare spots of coating asphalt are exposed on the surface of the shingles.
Bare spots will weather and begin to de-gradate with solar exposure over time. Degradation of the reinforcement mat can then result in interior damages if accompanied with failure of the underlayment and flashings.
The life expectancy of a shingle roof depends upon many factors including but not limited to the quality of the reinforcement material, the color of the granules, the roof pitch, the amount of ultraviolet exposure that the slope experiences due to its orientation, and the adequacy of the attic ventilation. As roof shingles age, they may exhibit blistering, flaking, cupping, clawing, splitting, cracking, and general granule loss.
During hail/wind storm events shingled roofs can indeed be damaged. The damage can be influenced by factors such as the age and preexisting conditions of the shingles. Also, it is common for shingle damage/conditions to be falsely attributed to hail impact or wind forces. The following conditions are often mistaken for wind or hail damage. Some of these conditions are further described below:
Drip edges of corrosion-resistant material metal protect the roof edge. Roofing construction guidelines indicate that shingles should overhang the drip edge. The tape over the self-sealing adhesives should be removed allowing for the shingles to self-seal. To assure proper maximum wind performance, shingles must be installed on to a properly installed deck. Lack of proper attic ventilation and/or improper roof deck installation will likely caused thermal stresses and accelerated aging of the shingles.
Following the manufacturer’s requirements and the applicable building code are also required. Building code guidelines in effect at the time of installation including the number, type and placement of fasteners should be adhered to. Fasteners should be non-corrosive.
When nails are used as fasteners, nails should have a minimum nominal shank diameter of 12 gauge (0.105”) and a minimum head diameter of 3/8”, be corrosion resistant, and penetrate 3/4” into the roof deck. Where the deck is less than 3/4” thick, the nail should be long enough to penetrate fully and extend at least 1/8” through the roof deck.
Having an understanding of shingle design and proper installation of shingles is extremely important in conducting a hail/wind roof damage claim. An investigation by your local I-ENG-A member can help determine the origin and cause of damaged shingles.
WHY LIGHT POLE FATALITIES CONTINUE TO HAPPEN
By: James 'M' Mike Surratt, PE, Carolina Investigative Engineers, PLLC
Electrical accidents continue to happen with light poles in parking lots, parks, and sidewalks. Many of these incidents involve small children and develop into high profile cases. The metal poles are supposedly “grounded” but are still electrically hot. What is the problem?
According to Power Quality Testing , LLC, in Washington, one in every 337 light poles is unsafe. Could the issue be the word “grounding” and interpretations by non-trained individuals? The National Electrical Code (NEC) requires all electrical equipment to be properly grounded. A maintenance person or an electrician helper wires a pole and drives a ground rod beside the pole and connects it to the pole. They then deem the pole to be properly grounded. However a building inspector should not approve this grounding installation, for good reason.
The NEC has become very specific in articles 250 and 300 concerning exactly what it takes to properly install and ground equipment. Relying on earth resistance from a ground rod to clear a fault is not allowed. The solution is to install another wire called a grounding conductor. This wire is a bare or green colored wire.
What is wrong with the ground rod? Why doesn’t it trip the breaker making the pole safe? First the ground rod is not for personnel protection. If a designer or local authority requires a ground rod for every pole, it is for lightning dissipation. Ground rods provide a low impedance path into the earth for lightning dissipation. If they were not there, lighting follows wiring paths inside to a structure. NEC requires a maximum of 25 ohm impedance for a properly installed ground rod. For a 50,000 volt lightning strike, a 25 ohms path is an easy route to take, but a pole at 120 volts a 25 ohm rod is tough to pass current.
Look at the following diagram which has a shorted pole. A fault current develops, using the earth as a path, back to the electric panel’s ground rod.
Properly installed ground rods meeting the code of 25 ohms, will provide a short circuit current of 120volts/(25ohm+25ohm)=2.4amps. This will not trip a 20amp breaker. The pole will stay continuously energized at 120v and is fatally dangerous for a child (with low impedance) to touch it. Remember, the short circuit current will flow through all resistance paths including a barefoot child with 2000 ohms resistance. Even an adult at 10,000ohms resistance would see 12 milliamps of current which is enough to interrupt heart function and cause fibrillation for some. The combined resistance of the rods will have to be 120v/20A < 6ohms to trip a 20A breaker. This is very unlikely unless the soil is wet and conductive.
Here’s what happens in a faulty installation: the black colored wire, supplying voltage, will accidentally touch the pole’s metal parts. The reasons are many but usually from a very old installation, poor installation, poor or lack of maintenance, or a pinched wire. When a low resistance ground conductor is provided back to the breaker panel, it completes a circuit. When the black wire touches the pole, a high current will develop and trip the feeding breaker. The pole is safe to touch and cannot be re-energized until the problem is corrected. With a ground wire having less than one ohm resistance, the breaker will trip immediately and clear the pole from ever staying accidentally energized.
The solution is that every metal pole has to be wired with three conductors so the ground (green or bare) wire provides a very low resistance to a short circuit rather than relying on the earth’s constantly changing resistance. When investigating a light pole electrical incident, one of the first places to look is to the ‘ground’. Many I-ENG-A member firms are well equipped to investigate and determine the origin and cause of this type of incident.
Stephen Ternullo & Associates, Inc.