216 Assessing Hail Damage

In general, damage to asphalt shingles, built up roofs (i.e., tar and gravel), asbestos cement shingles, cedar shingles, standing-seam terne metal roofs, slate, and red clay tiles that have been caused by severe hailstone impacts consist of impact craters and cracks and fissures originating at those craters.

Impact craters are where the impacts by hailstones have penetrated sufficiently into the material to breach its functional integrity and produce significant, permanent depressions or "dents." Generally, the associated cracks and fissures are larger in width at the point of impact and diminish in width and size with increasing distance away from the point of impact.

In asphalt shingles, hailstones sufficient in size to cause damaging impact craters to the top surface, can also cause damage to the back surface of the shingle, especially in the "tab" area of the shingle. The effect is similar to that observed when a BB impacts a pane of common glass: there is an obvious impact crater on the side on which the BB strikes, but there is also a conical "blowout" area on the opposite side. The blowout on the opposite side is due to momentum transfer via a compression wave through the material to the opposite surface. Because asphalt shingles are not brittle like glass, the effect is less pronounced but is observable in extreme cases. A similar effect has been noted on the moon and on Mercury, where the impact of a meteor was so severe, the shock waves caused damage at the corresponding antipode.

In the case of brittle materials, like red clay tiles, impact-associated cracks and fissures might look like star shaped cracks, where several cracks radiate outward from a central impact point. If impacts have been severe, the tiles might be fractured, broken, or even have holes knocked through them. Cracks and fissures that have been caused by hail impacts, should exhibit the same freshly exposed surfaces as those found in the hail impact crater, that is, they should be the same age.

Plate 21.5 Splits and cracks and curling in wood shakes caused by weathering. Note staple in circled area to hold down curled shake.

While often alleged to have been caused by hail or assumed to be sure indications of hail damage, the following conditions are not due to hail.

Curled and cupped shingles — This is when a shingle has curled up, especially in the portions of the shingle or wood shake that are exposed to sunlight. The effect is most pronounced in flatgrain shingles and shakes. Curling or cupping is due to drying out of the topmost layer of the shingle by ultraviolet light exposure. When the top layer dries out, it has less mass in it than before so it shrinks in size. Since the bottom layer is not exposed to ultraviolet light, it does not lose material and shrink. The tension created by the differential shrinkage between the top and bottom surfaces of the shingle or shake then causes the shingle or shake to curl or cup. Nailing a shake or shingle too high, too far from the edge, or improperly will accelerate the effect.

Cupping and curling is further exacerbated when the roof has been "shorted," that is, when the roof has been covered with fewer shakes or shingles than required by good practice. Usually this is done by increasing the amount of shingle or shake exposed to the sunlight, and decreasing the amount of shake or shingle that is covered by overlap with other shakes or shingles. Examination of the edge of a roof can often be useful in visually checking that the proper amount of overlap has been used, or by measuring the exposed portion of the shake or shingle.

For example, wood shake roofs using number 1 hand-split and resawn shakes that are 24 in. x 3/4 in. generally have an exposed portion measuring 7 1/2 inches long. Along the side of the roof, the roof thickness will appear to be four shakes thick (for a distance of about 2 inches) when counted upwards from the point of a shake along the bottom of the roof.

However, if the exposed portion of the shakes are increased just 1 inch-to 8 1/2-inches, the roof thickness along the edge will only appear to be three shakes thick when counted upward from the point of a shake along the bottom of the roof. By increasing the exposure by just 1 inch, the roofer uses about 13% fewer shakes, although the owner may have been charged a roof price based upon the proper number of shakes per "square" of roof area. By increasing the exposed area of the shakes, not only does the roof defraud the owner, but the shakes also dry out faster than normal. This means that they will curl and cup sooner, and the roof generally will wear out faster.

Shakes and shingles that have already become cupped or curled are more susceptible to cracking and splitting damage by hail impacts than shakes or shingles that are laying down in the usual way. This is because the curled portion of the shake or shingle is unsupported; it is basically a cantilever. Thus, a curled shake will absorb more of the impact energy imparted by the hailstone. However, when a wood shake or shingle roof is sufficiently curled to be more susceptible to hail damage, it is already in need of replacement regardless of the existence of any hail damage.

Plate 21.6 Curled asphalt shingles.

Buckled shingles — Buckled shingles, which have the opposite appearance of curled shingles, are usually the result of improper spacing of the shingles. During the summer when roof surface temperature may be quite hot, shingles expand. If the spacing is too tight to allow expansion, the shingles have no place to go but up, so they buckle. Similarly, wood shingles that are spaced too closely may also buckle, but for a slightly different reason. After a rain, wood shakes and shingles swell. Again, if the spacing is too tight and the wood shingles swell, they buckle. Often when shingles buckle, for either reason, they do not recover and remain buckled. Often, buckling will give a roof a rippled or wavy appearance.

Finding the stony cover of asphalt shingles in storm gutters — While hail impacts will cause some of the stony cover over asphalt singles to loosen and wash off, the same thing also occurs after a good rain. Sometimes no rain or hail fall is needed: the stones simply loosen and fall off due to differential expansion and contraction over time. Cheap shingles tend to lose their stony covers more easily than good-quality shingles. Thus, finding stony shingle cover particles in the rain gutters is not an indication that the roof has been damaged by hail and needs to be replaced. It does, however, indicate that the asphalt shingles have lost some of their cover as they normally do in a hard rain.

The purpose of the stony cover on asphalt shingles is to protect the underlying bitumen material from ultraviolet light exposure. Often, the primary difference between 30-year rated asphalt shingles and 10-year rated asphalt shingles is simply the thickness and adhesive strength of their stony

Plate 21.7 Asphalt-shingled roof with fungal growth on one side due to material from tree.

covers. In designing shingles, the loss of the stony cover over time, and after particularly hard rains and hail falls, is taken into consideration by the manufacturer. Finding stony material in the gutters does not automatically mean a new roof is required, or that its life has been otherwise significantly shortened.

Cracking, splits, and checks — Cracking of asphalt shingles and pitch membranes can be due to a number of causes. Cracks caused by hail impacts usually emanate from an obvious hailstone crater or impact point. The interior of the crack will be unweathered just like the freshly exposed surface within the hail impact. It will also have an obvious color difference from similar weathered material.

Cracks are also caused by exposure to ultraviolet light, and subsequent shrinkage. Exposure to ultraviolet light causes the lighter hydrocarbons in the bitumen mix to break down, volatilize, and outgas. The loss of this material then causes the affected material to shrink.

These cracks tend to appear in somewhat regular patterns, especially in areas where there is regular exposure to sunlight, because the shrinkage rate is regular. Generally, the cracks initiate and are widest at the top surface, where exposure to ultraviolet sunlight is maximum, and diminish in width with depth into the material, where the ultraviolet light cannot penetrate. Because the cracks open slowly, as opposed to hail-produced cracks, which open all at once, the interior of these cracks will appear weathered and oxidized. They may even be filled with various types of outdoor debris.

Plate 21.8 Asphalt shingles that have lost their stony cover due to weathering.

In cases where cracking of the bitumen material is an issue, it is often useful to find an area of the roof that does not normally receive much sunshine, but which would have obviously received hail strikes. Such an area can then be compared to one that normally receives sunshine most of the day.

Dented tin work— Metal flashing, vent caps, and other light gauge metal items usually exhibit hail "dings" or dents no matter what size the hailstone. Many people will point out the dings and indicate that if the metal was dinged, then their roof must be badly damaged. While this is convenient logic when a settlement check is on the line, it is not true.

Hail does not damage everything equally. Each type of material responds differently to impacts from the small spheres of ice. The thin gage sheet metal material in a vent cap, for example, is very different from the thick bitumen material used for a roof membrane. By the way, in most cases, the fact that sheet metal items are dinged does not mean they have been damaged, as long as they can continue to keep out the rain and perform their function. In some case, there may be cosmetic issues that override functional issues. In general, however, most of the sheet metal caps and devices common to a roof top cannot be seen from the ground. Thus, cosmetic damage is not an issue.

Dings in tinwork can actually be very useful in conducting a hail damage investigation. Generally, the width of the ding in the sheet metal is about 1/2 the diameter of the hailstone that made it. By measuring the dings noted in tin work, especially unobstructed vent caps that present normal surfaces to the hail velocity vectors, the relative size of the hailstones can be reasonably estimated. Further, the distribution of hail dings on various tin items on a roof indicates the vector direction of the hail fall, and therefore the wind vector that was present during the hail fall. This can be very important if there is a question about when the hail in question occurred.

For example, consider the hypothetical case where Mr. Jones discovers that his roof is hail-damaged after he buys his home. He then waits for the next hail fall, and makes a claim for hail damage at that time.

According to local weather records, the hail fall on the date of the claim was composed of hailstones no larger than 1/2-inch along with strong winds from the west. Examination of his asphalt shingles finds hail craters that are 3/4-1 inch in size, but the associated cracks and fissures appear weathered on the inside instead of freshly exposed. Examination with a hand lens finds dead bugs, leaf debris, and shingle cover stones within the cracks. Examination of the tin on his roof finds that 2-inch hailstones fell from the east at some time, but that 1/2-inch hailstones also fell at some time from the west. A little more digging into the local weather records finds that 2-inch diameter hailstones last fell in the area 2 years before Mr. Jones bought the house, and that the winds were from the east. The roof was installed 1 year before the 2-inch hail fall, but no hail had fallen in the area in the meantime.

Gravel cover driven into a bituminous roof — Some roofers claim that hail can drive the gravel cover of a built-up roof into the asphalt membrane and underlying felt layers, causing penetrations and subsequent leakage of the roof. Hail cannot do this. In a collision between an irregularly shaped rock in a gravel cover and an irregularly spherical hailstone, the contact is

Plate 21.9 Hail dents in metal roof.

not sufficiently clean for all the momentum of the hailstone to be transferred to the surface rock, and then directly to the one below it, and so on. In fact, when the two do collide, the hailstone usually shatters, or glances off into another nearby rock.

The primary purpose of a gravel overlay is to protect the roof from ultraviolet light. The secondary purpose of the gravel is to absorb hail impacts. A hailstone impacting into a pile of loose gravel simply dissipates its impact energy impacting and ricocheting among the surface rocks, which in turn, have more collisions with the rocks under them. As a rule of thumb, the impact energy of the hailstone expands as a 45-degree cone through the gravel cover.

In other words, if a 1-inch diameter hailstone impacts a gravel cover that is 1-inch deep, the impact energy will be spread over an area of 0.20 square inches at the surface where contact is first made, but will then expand to an area of 4.9 square inches at the surface of the bitumen. Of course by then, all the impact energy will have been dissipated by the friction between the rocks.

This point is easily demonstrable by having a person throw a hail-sized piece of ice as hard has he can into a layer of gravel, and then examining the underlying membrane to see if any gravel has been driven into the bitumen.

The usual reason for gravel to be pushed into the roofing membrane is direct bearing loads, usually caused by people walking on the gravel or by heavy loads being supported by small "feet" or blocks resting on the gravel. A 200-pound roofer can easily mash gravel into the roof with the heel of his boot. In cases where such claims have been made, sweeping the gravel back often reveals that the only places where gravel has been mashed into the bitumen is where there has been foot traffic on the roof.

In assessing hail damage, the value of examining collateral damage should not be overlooked. Collateral damage is damage that has been caused to nearby things by the same hail fall. For example, if the roof of a house has endured a damaging hail fall, the garage in the backyard with the same kind of roof will likely exhibit the same kind of damage. Evidence of 1.25-inch diameter hailstone impacts on the roof, will likely be corroborated by finding burnish marks on the air conditioner cabinet in the side yard, also indicating a hailstone diameter of 1.25 inches.

Collateral damage can be very helpful in establishing the time frame for a particular hail fall. For example, consider the situation where Mr. Jones claims that the severe hail damage on his roof was from the most recent hail fall, yet the Smith's house across the street, which has a roof less than a year old, exhibits no sign of hail damage, and neither does the new deck recently added on to the Murphy's house next door. Can the same hail fall that damaged the Jones' house fail to cause any noticeable damage to the house across the street, or to the deck next door?

Plate 21.10 Worn and rotted shakes with small burnish marks (circled). There is a green color, which is due to fungus eating into the shakes.
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