Webinar Questions & Answers: Investigating Wind & Hail Damage

Transcription

1 Webinar Questions & Answers: Investigating Wind & Hail Damage Section A: Hail 1. Can hail direction change in a single storm, damaging all slopes of a structure? Hail can fall straight down or at an angle, depending on wind speed and storm movement. Hailproducing thunderstorms can change direction, but if you watch images of radar, the direction is generally consistent, and any change in direction is minimal. These storms may damage only one or two directional slopes, depending on the wind speeds and roof slopes. Finally, a particular storm cell is going to affect a particular property for only a short period of time (minutes). It is improbable that a storm will radically change direction while it is over a single house, thus allowing hail to impact it from different directions. Of course, if it did, the dents and clean spots on the collateral surfaces would reflect the direction of hail impact. 2. What makes a rake more susceptible to hail damage than field shingles? Along the rake, the shingles typically overhang the roof edge by ½ to ¾ inch. This part of the shingle is not backed by the roof decking. Since it is unsupported, it is more easily damaged. The edges of eave shingles are similar (Figures 1 and 2). Field shingles are typically flat against the decking and will not deform as easily. Keep in mind, the surface area of the unsupported eaves and rakes is small compared to the overall roof area; it is possible to have hail damage to field shingles without damage to the shingles edges overhanging the eaves and rakes. Because ridge and hip shingles typically contain more surface area, damage is more common to these shingles. Figure 1: Hail Damage to an Unsupported Rake Shingle

2 Hail Impacts Figure 2: Hail Damage to an Unsupported Eave Shingle 3. Does hail impact affect organic tabs differently than composition tabs? Many times the tabs exhibit granular loss when we're inspecting the roof for hail. Hail damage to an organic-mat shingle is similar to a fiberglass-mat shingle; the resulting bruises look similar for both types of shingles, but the damage to an organic shingle will typically show more deformation (depth of the indentation). The physics are the same. Fiberglass-mat shingles are stronger and therefore require larger hail to cause damage. Because of the organic mat, these shingles deteriorate more rapidly than fiberglass-mat shingles. This deterioration is more common in areas with more water (e.g., valleys) and more sun exposure (south-facing slopes). Deterioration of organic-mat shingles results in granule loss and delamination of the shingles (Figures 3 and 4).

3 Figure 3: Hail Damage to an Organic-Mat Shingle Figure 4: Organic-Mat Deterioration

4 4. Do you have any tricks for exposing hail damage to aluminum siding that is visible only during certain times of the day? Shining a high-powered flashlight or spotlight at an angle to the siding typically produces the best result. Water can also be sprayed on the siding to show the dents. Chalk can be used to outline the dents. If using chalk, be careful not to scratch the siding. 5. Is there a rule-of-thumb for the number of hits in a specific sample area that indicates that an entire slope should be replaced? The short answer is no. The decision to repair or replace should be based on two issues. First, are the shingles pliable enough that they can be lifted to remove and install nails? Generally, you need to lift a shingle only about 45 degrees to remove and replace the nail. Shingle pliability will vary with temperature. Let the sun warm the shingles before checking whether they are pliable. Second, the repair-versus-replace decision should be determined by a cost analysis. Basically, what is the cost per shingle to replace, what is the number of damaged shingles per slope, and what is the cost to replace the entire slope? 6. Can you give any tips for determining what is legitimate hail damage to window claddings? Holes or cracks in the cladding that allow water intrusion are functional hail damage to window cladding. Dents in metal or abrasions on wood are cosmetic. In our reports, we distinguish between functional damage and cosmetic impacts. The location of the dents or abrasions matters. Hail can fall vertically or at an angle. When it does fall at an angle, it is typically close to vertical. For example, 1-inch-diameter hail with a 30-mile-per-hour wind will fall at approximately 30 degrees from vertical. If the window is protected by an overhang, it is more probable that impacts to window claddings will be at the bottom half of the window. Horizontal cladding edges are more easily dented (Figure 5). The locations of the dents should also correspond to the direction of hail impact and other collateral indicators. Furthermore, all of the windows on the same side of the house, with the same cladding and exposure, should have similar dents. Man-made damage is typically in easily accessible areas. Look at second-story windows or other areas that are not easily accesible to foot traffic. Finally, hail dents in metal surfaces such as window claddings, metal siding, and downspouts are wide, shallow dents. Deep dents, dents with creases, and dents with surface scratches are not consistent with hail impact.

5 Figure 5: Hail-Impact Locations on Window Cladding 7. How much does the age of a roof affect the size of hail it can withstand? First, let s review some numbers on hail impact: 1-inch-diameter hail has an impact energy of approximately 1 foot-pound; ¾-inch-diameter hail has an impact energy of 0.5 foot-pound; and ½-inch hail has an impact energy of 0.1 foot-pound. In other words, 1-inch hail has TWICE as much impact energy as ¾-inch hail and TEN TIMES as much energy as ½-inch hail. That means that age-related weathering would need to radically reduce the shingles ability to withstand hail impact. A laboratory study on 11-year-old, field weatherered aphalt shingles has shown no decrease in their resistance to hail impact. In other words, the science does not support that older shingles are more susceptible to hail damage. Shingles become brittle as they age. The study cited above was on 11-year-old shingles. It is possible that shingles near the end of their useful service life (e.g., 20+ years) are brittle enough that they are more prone to damage. Considering the significant difference in the impact energy with small changes in hail diameter, it is not probable that smaller hail will damage older shingles. 8. Could you speak to the variability of hail density/hardness as it relates to the size of hailstones necessary to cause damage? The density of hail can vary depending on the conditions under which it is formed. The weight of the hail directly affects its impact energy, and the weight is a function of density. Laboratory studies have measured naturally occurring hail with densities as low as 0.33 gram per cubic centimeter (g/cm 3 ). Other studies have measured hailstones with densities between 0.82 and

6 0.87 g/cm 3. Laboratory studies that shoot ice balls at roofing materials use freezer-created, spherical ice balls. These ice balls have the density of bulk ice, approximately 0.9 g/cm 3. Density matters. If the natural hailstone is less dense, the same size hailstone that damages shingles in laboratory study might not damage shingles in the field. Once again, if asphalt shingles are hail damaged, you will find a visible impact point where the damage can be seen and measured. 9. Wouldn't you see some granules pushed in if you have an impact from hail? The science doesn t answer this question (note that I keep returning to the science). Granules are embedded in the asphalt during the manufacturing process. In my own experience, I have never seen granules pushed into the asphalt. Even when hit with a hammer, the granules are typically crushed or displaced rather than pushed into the asphalt. In my field experience, even large hail (2 inches or greater) simply removes granules. The fracture in Figure 6 is from at least 2-inch hail on a relatively new dimensional-style shingle. Note that the fiberglass is exposed, the mat is fractured, and granules are removed. However, no granules are pushed into the asphalt as a result of the hail impact. Figure 6: Hail Fracture from at Least 2-inch Hail

7 Section B: Wind 1. Why do the corners of the far left tab of a three-tab shingle lift while the remainder of the shingle does not? Seal strips on shingles fail, typically as a result of age-related deterioration. Patterns on the unsealed shingles become noticeable when shingles are installed using the vertical-racking method, in which the shingles are installed in single columns up the slope (Figure 7). As a result, the butt joints on the shingles show up in every other course (yellow line in Figure 7). The butt joints are where two shingles in the same course meet. Along the racking line, the shingles in Column 1 and Column 2 will expand and contract in opposite directions, across the slope. The shingle overlying the butt edge is sealed to both columns. As a result, the seals typically fail first at this butt edge, along the racking line. Notice that the corners of shingles in Figure 7 are unsealed at alternating angles. Sometimes, the entire shingle tab is unsealed, as indicated by the straight white lines. Figure 7: Shingle Racking Line 2. At what wind speed and for how long should shingles withstand the wind before they are damaged? The standard tests for wind resistance of asphalt shingles are ASTM D3161 and ASTM D7158. In ASTM D3161, the shingles are subjected to constant wind speeds (60 to 110 mph) for 2 hours. In ASTM D7158, the uplift force is calculated for specific wind velocities, and this is compared

8 to the measured uplift resistance of the shingles. These tests are performed on new, fully adhered shingles, and the tests do not account for the age-related deterioration of the seal strips (hence the limited wind warranties). Studies have shown that a statistically significant number of shingles are unsealed after six years, and the percentage of unsealed shingles increases over time. Therefore, the shingle rating does not reflect actual performance of shingles that have been in service for a number of years. In addition, winds are variable, and testing with a constant wind speed does not reflect in-service conditions. Table 1 lists the ASTM classifications and wind ratings. The ratings do not reflect that these shingles will withstand sustained winds at these speeds in real-world conditions. Remember that the performance of the shingle is dependent on proper installation. Shingles with improper nailing or shingles installed where the seal strip does not properly activate will not perform as intended. So, to answer question, many variables determine how a shingle will perform in the field. And shingles may not resist the rated wind speed. The higher-rated shingles, if properly installed, should perform better. Wind Speed ASTM D3161 ASTM D mph Class A mph Class D Class D 110 mph Class F mph -- Class G 150 mph -- Class H Table 1: ASTM Wind Speed Classifications 3. Is the wind resistance rating of shingles a factor, or are all shingles rated for high resistance? As stated above, the ratings do matter, and different shingles are rated for different speeds. Also worth repeating, the performance of the shingles is dependent on proper installation and the time-related deterioration of seal strips. Shingles with a higher rating should perform better. For example, one major manufacturer produces a three-tab shingle with a 60 mph rating, based on installing four nails per shingle. If installed correctly, nails in one course will penetrate the underlying shingle, so all shingles should have eight nails (two rows) per shingle (note that some installations require more fasteners and additional adhesive). The wind resistance of these shingles is warrantied for only five years. Note that seal strips can begin to fail five to seven years after installation, and, once the seal strip fails, three-tab shingles are more vulnerable to wind damage than dimensional-style shingles. Most manufacturers produce dimensional shingles with ratings from 110 mph to 150 mph, with warranties that typically do not exceed 15 years.

9 4. Are shingles sliding down the slope an indication of improper installation? Many roofers claim it to be wind damage. Wind creates an uplift force on roof slopes generally less than a 9:12 pitch and pushes against the roof on higher-pitched slopes. Shingle movement down a slope (sliding) is not consistent with the force applied by wind. For three-tab shingles, especially if unsealed, once the shingle tab lifts, the wind creates a pressure against the tab that results in bending. This is why individual three-tab shingles crease, tear, or are removed from a roof, sometimes from multiple wind events. If a shingle moves down the slope, gravity is the culprit. Typically, this type of movement occurs on steeper slopes, 8:12 or greater. It is also more common for dimensional shingles, as they are heavier than three-tab shingles. However, the nail requirements are the same: four nails per row with a total of two rows and eight nails per shingle. Since dimensional shingles are heavier, they are more likely to slide. Figure 8 shows typical installation requirements for a dimensional shingle. If shingles are high-nailed, the nails will not penetrate the underlying shingle. Instead of eight nails, each shingle will have only four nails. When shingles are installed by vertically racking, the last nail in every other course cannot be installed until the next column of shingles is installed. This is because the shingle needs to be lifted to slide in the adjacent shingle in the next column. Often this nail, referred to as the blind nail, is left out. Thus, instead of eight nails per shingle, you might end up with only three nails per shingle. Figure 8: Typical Dimensional Shingle Nail Placement The force that causes shingles to slide down a slope is gravity, not wind, and the cause is typically improper nailing. Once shingles are sliding, they are more susceptible to wind damage. If shingles are removed from the roof, I, as a forensic engineer, have to determine whether they came off the roof as a result of gravity or wind. In both situations, improper nailing can be an underlying problem. Determining whether the shingles are sliding as a result of improper nailing, have been removed from the roof as a result of wind, or both requires examining the unique circumstances on each roof.

10 5. On ridge shingles, is there a scenario in which the ridge shingles would tear across the body instead of the creasing typical on the tabs? Ridge and hip cap shingles are often the first shingles damaged by wind. Uplift pressures can be highest in these areas. Ridge and hip shingles have the same problems as field shingles; the seal strips fail over time. In addition, these shingles are bent during installation, which can result in inadequate adhesion of the seal strip. Creasing of hip and ridge shingles from wind can often result in diagonal creases. At the top of the ridge, the shingle is bent over the ridge, which acts as a rigid point. The overlying cap shingle prevents uplift, and the nail is typically installed in this area. If the seal strip has failed or is not adequate, the shingle is prone to bending at an approximate 45-degree angle. This diagonal creasing can result in tearing along the same line. Because the cap shingles are overlapping, the uplift or removal of one cap shingle can result in a cascading effect that removes a section of cap shingles. If the cap shingle tears, it can be along these diagonal creasing lines. Irregular tears can be an indication of man-made damage. As with so many things in the field, you must consider what the overall picture tells you. Is there collateral damage from a wind event? Does the damage fit a pattern consistent with wind? 6. Is resealing a shingle a proper repair? First, to be clear, unsealed shingles are not damaged. As stated before, seal strips fail for many reasons. Second, yes, unsealed shingles can be resealed. Most shingle manufacturers state that unsealed shingles can be hand sealed, and they provide specific instructions on how to reseal these shingles. 7. Is debris embedded under shingle tabs (pine needles, leaves, etc.) a good indicator of potential wind damage to a shingle(s) that may have later sealed itself partially back down? No. As a general rule, unsealed shingles don t reseal, especially if they have become unsealed as a result of age-related deterioration of the seal strip. In fact, if shingles don t seal soon after installation, they may never seal. Shingle manufacturers state that shingles should be installed when the air temperature is high enough to cause the seals to activate. Debris under a shingle is simply an indicator of debris under the shingle. If the shingle is not creased, torn, uplifted from the nails, or removed from the roof, it is not wind damaged. 8. If the shingle seals have failed, and wind causes the shingles to crease or tear, are the shingles considered wind damaged, or is this considered wear and tear? Unsealed shingles are more susceptible to wind damage because the seal strip is part of the designed wind resistance of the shingle. In addition, once the shingle lifts, additional wind forces are applied to the shingle. For example, a three-tab shingle may be rated for 60 mph winds when sealed, but if the shingle is unsealed, lower wind speeds can damage the shingle once it is lifted. Again, unsealed shingles are not damaged. Damage is a reduction in the functionality (water-shedding capacity) or service life of the component. Unsealed shingles shed

11 water and will last as long as sealed shingles (weathering). So the question is really, What is the mechanism that caused the shingle to crease, tear, or come off the roof? Unsealed shingles don t crease or tear without an applied force. Another good question to apply is, If the wind event didn t happen, would the shingles be creased, torn, or missing? If wind causes the shingles to crease, tear, or come off the roof, they are wind damaged. Underlying causes may have made them susceptible, but if the wind event didn t happen, the shingles would not have been damaged. Section C: General 1. How can you tell the difference between a 20-year and a 25-year shingle? Shingles are sold as 20-year, 25-year, 30-year all the way up to lifetime. The shingles don t last as long as the names imply. Shingle gauges or calipers can measure the thickness and estimate what type of shingle is on the roof, but a thickness measurement is only an approximation. The best method is to identify the shingle brand and style through markings on the shingle itself. This information can sometimes be found on the back of the shingle. Some companies will match a shingle sample. It never hurts to ask the property owner whether they have any leftover shingles from the installation. The packaging can be a good indication of what type of shingle was installed. The quality of a shingle depends on more than its thickness. The quality of the components, including the asphalt and the fiberglass mat, affect the lifespan of the shingle.