P 9.2 HAIL DAMAGE TO TILE ROOFING
Timothy P. Marshall*, Richard F. Herzog, Scott J. Morrison, and Steven R. Smith
Haag Engineering Co.
Roofing tile is popular especially in the southern
U.S. due to its resistance to fire, heat, and moisture, as
well as its long service life. The first clay roofing tiles
were produced in Asia and later in Europe several
thousand years ago. Hobson (2001) indicated the first
clay tiles produced in the U.S. were in 1650 in the
upper Hudson River Valley. Concrete roofing tiles
didn't appear until around 1848 in Germany and
commercial production began soon after in Bavaria.
However, within the past twenty years, dozens of new
tile products have been developed comprised of
lightweight concrete and wood-fiber cement. Many of
these newer products have performed poorly when
exposed to the weather for only a short period of time.
Moisture damage to tiles has involved surface peeling,
delamination, erosion, and pitting, just to name a few
problems. When a hailstorm occurs, damage
inspectors unfamiliar with these products can
erroneously conclude that certain anomalies with the
roofing tile had been caused by hail.
We have undertaken a study of various roofing tiles
in an effort to document the effects of hail. Ice ball
impact tests were conducted on many different roofing
tiles and compared with our field observations from
thousands of roof inspections over the past twenty
years. In this paper, we will summarize the
characteristics of hail-caused damage to various
roofing tiles and distinguish them from conditions that
occur in tile manufacturing, installation, and/or
2. ICE BALL IMPACT TESTING
Laurie (1960) was one of the first to conduct ice ball
impact tests on roofing tiles. He produced spherical
and cubical ice stones of 2.5 in. (5.1 cm) in diameter
and launched them with compressed air using a
modified grenade thrower. He impact tested concrete
and clay tiles among other types of roofing products.
Greenfeld (1969) conducted a series of ice ball
impact tests on various roofing materials using a
commercially available compressed air gun. Ice balls
in 1/4 in. (.6 cm) increments were made from molds
between 1 in. (2.5 cm) and 3 in. (7.6 cm) in diameter.
Among the roofing materials tested were asbestos-
cement shingles and red clay tiles. He defined failure
as a crack in the material and was able to damage 1/8
in. (.3 cm) thick asbestos cement tiles with 1.5 in. (3.8
cm) ice balls and crack unsupported areas on clay tiles
with 1.75 in. (4.5 cm) ice balls.
*Corresponding author address: Timothy P. Marshall,
2455 McIver Ln., Carrollton, TX 75006. Email:
Koontz (1992) performed ice ball impact tests on
various concrete tiles using a compressed air gun
similar to Greenfeld. He found that all tiles tested
exhibited fairly high degrees of impact resistance.
Fracture of the material did not occur even with 2.5 in.
(6.4 cm) ice balls propelled at around 80 mph (36 ms-1).
However, he was able to break the tiles when he
increased the velocities of the ice balls to 89 mph (40
m/s-1). He found that flat concrete tiles were more
impact resistant than S-shaped tiles.
The authors' firm conducted numerous ice ball
impact tests on various concrete tiles beginning in
1992. Additional impact tests were conducted for this
study. Our firm developed a mechanical device
dubbed the IBL-7 (Ice Ball Launcher – 7th generation)
that launched ice balls on a track employing multiple
bands of latex tubing (Figure 1). The tubing ensured
consistency in launch velocity and the track guided
each ice ball to the desired target point. This was an
improvement over compressed air guns utilized in
earlier tests, as it was difficult to control the launch
velocities of the ice balls using compressed air.
An ice ball was placed into a plastic holder that kept
the ball in place while it accelerated forward. The
holder was stopped at the end of the track allowing the
ice ball to continue forward. Desired velocities of the
ice ball were obtained by controlling the tension on the
latex tubing. The velocities of the ice balls were
measured by a chronograph mounted on a tripod at the
end of the launcher. Target launch velocities are
shown in Table 1. Generally, the ice balls were
produced by freezing tap water in molds, and they were
harder and denser than natural hailstones (Figure 2).
Figure 1. Ice ball launching (IBL-7) device with light
sensors (chronograph) developed for impact testing.
Ball diameter Target Velocity Energy
in. cm. Mi./hr. M/sec. Ft-lbs.
.75 1.9 42.3 18.9 0.44
1.00 2.5 49.8 22.3 1.43
1.25 3.2 55.9 25.0 3.53
1.50 3.8 61.4 27.4 7.35
1.75 4.5 66.2 29.6 13.56
2.00 5.1 71.6 32.0 23.71
2.25 5.8 76.0 34.0 37.73
2.50 6.4 79.8 36.7 57.48
Table 1. Terminal velocities and energies of ice balls
utilized in this study.
Figure 2. Solid ice balls made in rubber molds were
utilized for impact testing on roofing products.
3. CONCRETE ROOFING TILE
3.1 Ice ball impact tests
A total of 13 different concrete tile products were
tested. Tiles had various profiles including mission S,
double S, flat, and flat-ribbed (Figure 3). Each tile had
overall dimensions of 17 in. (44 cm) in length, 12-3/8 in.
(1.4 cm) in width, and up to 1 in. (2.5 cm) thick. Tiles
had interlocking side joints up to 1 in. (2.5 cm) wide by
1/2 in. (1.3 cm) thick and would overlap the adjacent
tiles. The tiles were installed on test panels per
manufacturer specifications and subjected to ice ball
impacts using the IBL-7. Tiles were impacted
perpendicularly in the field, along the overlaps, and in
the lower right corners (when looking upslope) using
ice balls ranging from .75 to 2.5 in. (1.9 to 6.4 cm) in
Figure 3. Concrete tile testing: a) sample test panel,
and b) tile breakage after ice ball impact.
Damage to the concrete tile was defined as a
fracture in the material. Typically, multiple irregular
fractures emanated from the impact point. Fractures
that occurred above the headlap were functional
damage as the water shedding ability of the tile had
been compromised. Table 2 shows a summary of our
ice ball impact tests for one of the concrete tile
ICE BALL IMPACT TEST RESULTS
1 1.50 .0575 94 7.90 No
2 1.50 .0605 92 7.96 No
3 1.50 .0600 92 7.89 No
4 1.75 .0990 100 15.39 No
5 1.75 .0930 101 14.74 No
6 1.75 .1020 99 15.54 Yes
7 2.00 .1505 111 28.82 Yes
8 2.00 .1400 112 27.29 No
9 2.00 .1385 113 27.49 Yes
Table 2. Concrete S-tile ice ball impact test results on
one of the 13 different products tested.
In summary, none of the concrete tiles tested were
fractured by 1 in. (2.5 cm) diameter ice balls, even in
their most sensitive locations. Four of the 13 tiles were
fractured at their corners with ice balls as small as 1.25
in. (3.2 cm) in diameter. Six of the 13 tiles remained
unbroken when impacted with 1.50 in. (3.8 cm)
diameter ice balls. Ice balls of 2.5 in. (6.4 cm) in
diameter broke all tiles. These test results correlated
well with our observations of concrete tile roofs after
actual hailstorms (Figure 4).
Figure 4. Hail damage to concrete tiles: a) shattered
tiles from a single impact, b) shattered tile edge
associated with a hail-caused spatter mark, c) large
half-moon shaped fracture along the tile overlap, and d)
small half-moon shaped fracture along the tile overlap.
3.2 Curved corner fractures in concrete tiles
The authors have discovered that curved corner
fractures are inherent in many concrete tile roofs.
These cracks emanate from the lower right corners of
the tiles and have a variety of causes (Figure 5). We
have found right corner fractures with all types of
interlocking tile profiles. Occasionally, inspectors
mistakenly identify this phenomenon as hail damage.
Close examination usually reveals algae or dirt in the
fractures thereby indicating old damage. Sometimes,
tile corners are reattached with caulking or cement.
Figure 5. Curved right corner fractures in concrete
tiles that were not the result of hailstone impact.
One cause of right corner fractures is shunting the
tiles together so that they butt tight with no room for
expansion. Tiles need room to expand with increasing
temperature and moisture. One can expect a 50 ft. (15
m) length of tiles to expand roughly .2 in (.5 cm) due to
a change of 50 F (10 C). Without providing room to
accommodate expansion, tiles press against each
other. The resulting strains can fracture the thinner
overlap region on the tile, especially at the lower right
(when looking upslope) corners. Thus, tiles with
interlocking side joints should be installed with
maximum "play" in order to accommodate for lateral
movement. We also have found that persons walking
on the tiles can also cause right corner fractures. In
most instances, the fractured corners remain below the
headlap regions and do not result in water infiltration.
However, less common secondary fractures have been
discovered in the tile overlaps extending above the
headlap regions (Figure 6).
Figure 6. Primary and secondary right corner
fractures in flat concrete tile.
There are two additional factors in the design of
concrete tiles that can promote right corner fractures.
One factor is a shrinkage crack that forms as the tile
dries unevenly. Tiles with interlocking side joints do not
have a uniform thickness in cross section. Thus, as
these tiles dry, the thin, outer edges of the tiles dry first
and the thicker portions dry last. In particular, the
interlocking side joints cure first since this area has the
greatest surface area-to-volume ratio. In contrast, the
thicker portion of the tile, containing head and nose
lugs, dries last since this area has the smallest surface
area-to-volume ratio. The relative time differences in
drying/curing can create internal stresses that lead to
shrinkage cracks (Figure 7). The authors have found
small shrinkage cracks in new tiles. The cracks
became more obvious when tiles were misted with
water and the water-filled cracks dried slowly.
Figure 7. Surface area-to-volume ratios shown in right
half of a flat tile. In general, the higher the area-to-
volume ratio, the quicker the tile dries. In this case, the
overlap dries first, especially at the corners.
Another factor that can cause right corner cracks is
a small nub that extends from the lower left corner on
the adjacent tile (Figure 8). This nub is formed during
the manufacturing process when the tile is trimmed.
The nub acts as a stress concentration point as it bears
against the adjacent tile. The nub eliminates the room
necessary to accommodate for expansion due to
increasing temperature and moisture. The resulting
strains promote curved cracks across the overlapping
portion of the tile.
Figure 8. Nub projecting from bottom left corner of
adjacent concrete tile can produce a stress
concentration point on the right corner of the adjacent
tile. This nub also can be observed in Figure 5 (d).
3.3 Additional concrete tile defects
There are a number of additional tile deficiencies
caused during the manufacturing process or installation
(Figure 9). Some concrete voids have rounded forms
that can be mistaken for hail damage. Persons walking
improperly on the tiles can break the tiles across their
widths. When walking on a tile roof, it is best to step
along the lower portion of the tile, where underlying
lugs provide firm support. In contrast, the center of the
tile has little underlying support and is easier to break
Figure 9. Concrete tile defects not caused by hail: a)
concrete void, b) lack of slurry coat, c) missing tile
corner, and d) broken tiles from foot traffic.
4. CLAY ROOFING TILE
4.1 Ice ball impact tests
A test panel with Spanish clay tiles was constructed
and impacted with various size ice balls using the IBL-
7. The tiles were hung on nails on a wooden roof deck
(Figure 10). Tiles were impacted perpendicularly in the
field and in the lower right corners using ice balls of
1.25 and 1.5 in. (3.2 and 3.8 cm) in diameter. Damage
to the tiles involved breaking or shattering of the
product. Multiple fractures occurred in the tiles and
fractures were irregular, emanating from the impact
Figure 10. Clay tile testing: a) test panel, and b)
shattered nose or bottom edge of tile after impact.
Table 3 summarizes our impact test results on clay
roofing tiles. No tile fractures occurred when impacted
with 1.25 in. (3.2 cm) ice balls. However, all tile
corners broke with 1.50 in. (3.8 cm) ice balls. Field
areas of the tiles were more impact resistant than the
ICE BALL IMPACT TEST RESULTS
1 1.25 .0335 85 3.76 No
2 1.25 .0345 85 3.78 No
3 1.25 .0350 84 3.84 No
4 1.50 .0595 95 8.35 No
5 1.50 .0610 93 8.20 No
6 1.50 .0610 94 8.38 No
7 1.50 .0600 92 7.96 Yes*
8 1.50 .0605 93 8.07 Yes*
9 1.50 .0615 93 8.27 Yes*
Table 3. Clay S-tile impact test results.
4.2 Clay tile deficiencies
Clay tiles are prone to pitting or spalling due to
freeze-thaw effects especially if they are deteriorated.
Small voids and material inclusions absorb moisture
and expand during freezing conditions. Some of these
spots can take on rounded forms and be misidentified
as hail-caused damage. Occasionally, rough areas on
tile surfaces form when they are manufactured (Figure
Figure 11. Clay tile deficiencies not caused by hail: a)
lack of glazing, b) pitting, c) spalling, and d) void in the
tile when made.
5. WOOD FIBER-CEMENT ROOFING TILE
5.1 Ice ball impact tests
A test panel with wood fiber-cement tiles was
constructed and impacted with various size ice balls
using the IBL-7 (Figure 12). Individual tiles were 18 in.
long (46 cm) and 8 or 12 in. wide (20 or 30 cm) by 1/4
in. (.6 cm) thick. Tiles had a wood grain pattern on
their top surfaces that resembled cedar shingles. The
tiles were fastened to a wooden roof deck over a felt
underlayment. Tiles were impacted perpendicularly in
the field and in the lower corners using ice balls of .75,
1, and 1.25 in. (1.9, 2.5, and 3.2 cm) in diameter.
Damage to wood fiber-cement tile involved an
indentation with fracturing of the tile layers.
Figure 12. Wood fiber-cement testing: a) test panel,
and b) indentation produced by 1.5 in. (4.5 cm) ice ball.
Table 4 summarizes our impact test results on wood
fiber-cement roofing tiles. No tile fractures occurred
when impacted with .75 in. (1.9 cm) ice balls. However,
all tiles were indented or fractured with 1.50 in (3.8 cm)
WOOD FIBER-CEMENT TILE
ICE BALL IMPACT TEST RESULTS
1 1.00 .0175 76 1.57 No
2 1.00 .0180 76 1.62 No
3 1.00 .0185 76 1.66 No
4 1.25 .0335 84 3.67 No
5 1.25 .0340 84 3.73 No
6 1.25 .0340 86 3.91 No
7 1.50 .0605 93 8.13 Yes
8 1.50 .0615 93 8.27 Yes
9 1.50 .0620 95 8.70 Yes
Table 4. Ice ball impact test results on wood-fiber
We found that wood fiber-cement tiles were softer
than their concrete and clay counterparts and readily
dented. There also were brittle-type fractures with half
moon-shaped fractures along the tile edges. These
observations correlated well with our field inspections
of such roofs (Figure 13).
Figure 13. Hail damage to wood fiber-cement tiles: a)
indentations, b) closer view of indentation, c) half
moon-shaped fracture at edge, and d) broken ridge tile.
5.2 Deterioration of wood fiber-cement tile
The authors have determined that a number of
wood-fiber cement tile products have deteriorated
rapidly with exposure to moisture and freeze/thaw
effects. These thin tile products can peel, erode, and
delaminate in as little as six years of normal weather
exposure. Some aspects of tile deterioration take on
rounded forms that can be misidentified as hail-caused
damage (Figure 14). Murphy (2002) discusses the
deterioration effects of blue-green algae on fiber-
Figure 14. Deterioration effects on wood fiber-cement
tiles, not caused by hail: a) dark blotches, b) white
blotches, c) surface peeling, and d) pitting/erosion as
well as edge delamination.
5.3 Mechanical damage to wood fiber-cement tiles
Wood fiber-cement tiles frequently are installed on
steep roof slopes that are not walkable. Installers
attach toe-boards to the roof in order to install the
roofing tiles and removed them after the tiles are
installed. Since the tiles are relatively soft or brittle,
they are relatively easy to damage. We have identified
various mechanical damages to wood fiber-cement tile
roofs caused when the roof was installed. Such
problems include broken corners, gouges, nail holes,
overdriven staples, and footfall damage (Figure 15).
Figure 15. Mechanical damage to wood fiber-cement
tiles: a) broken corners and metal toe-board bracket, b)
foot broken tiles, c) chipped tile edge and nail hole, and
d) golf ball impacts.
We also have found a number of cases where the
tiles were indented by errant golf balls from a nearby
golf course. Such damage was not randomly
distributed on the roof but concentrated on the roof
slope nearest the golf course (Figure 16). The
indentations all were similar in size and shape, and a
golf ball could fit well inside the indentations. Hail falls
in various sizes and shapes and would not cause such
Figure 16. Case where errant golf balls damaged the
roof tiles as noted by Xs.
6. ASBESTOS-CEMENT ROOFING TILE
6.1 Ice ball impact testing
Asbestos-cement roofing tile no longer is
manufactured in the U.S. due to health concerns.
However, there are still a number of older buildings
covered with this product. These tiles have been
known to last more than 50 years. Asbestos resistance
to decay has made it desirable as a roofing product.
We have encountered a number of questions about the
characteristics of hail-caused damage and whether hail
impact of the roofing tile can lead to the exposure or
spreading of asbestos fibers.
In an effort to determine the impact resistance and
characteristics of hail damage of this product, a test
panel was constructed. Flat asbestos-cement tiles
were 13.75 in. (34.9 cm) long by 9.25 in. (24.5 cm)
wide by 1/8 in. (.32 cm) thick. The tiles were hung from
nails driven into a wooden roof deck over felt
underlayment. Tiles were impacted perpendicularly in
the field, along the bottom edges, and in the lower
corners using ice balls of 1.25, 1.5, 1.75 and 2 in. (3.2,
3.8, 4.4, and 5.1 cm) in diameter. Damage involved
fracturing the tile.
Table 5 summarizes our impact test results on
asbestos-cement tiles. We found these tiles were quite
resistant to hailstone impact. No tile fractures occurred
when impacted with 1.5 in. (3.80 cm) ice balls.
However, tile corners began breaking when impacted
by 1.75 in. (4.5 cm) ice balls.
ICE BALL IMPACT TEST RESULTS
1 1.25 0.034 85 3.76 No
2 1.50 0.058 93 7.80 No
3 1.50 0.058 93 7.80 No
4 1.50 0.058 93 7.80 No
5 1.50 0.058 92 7.76 No
6 1.75 0.101 101 16.01 Yes
7 1.75 0.099 101 15.62 No
8 1.75 0.099 102 15.83 Yes
9 2.00 0.147 113 29.17 Yes
Table 5. Ice ball impact test results on asbestos-
Asbestos-cement roofing tiles had the greatest hail
resistance among cementitious products tested in spite
of its small thickness. This conclusion has also been
confirmed in our field inspections of asbestos-cement
tile roofs (Figure 17).
Figure 17. Hail impacts to asbestos-cement products:
a) hail-caused spatter marks resulted in no damage, b)
indentation with fractures, c) puncture, and d) chipped
edge on ridge tile.
Spurny (1989) indicated that asbestos-cement
roofing tiles contain up to 12 percent of chrysotile
asbestos. He points out that such fibers constantly
shed from the tile surfaces due to the eroding action of
the wind, rain, sunshine, frost, and even exposure to
airborne pollutants. Bornemann and Hildebrandt
(1986) studied the wearing rates of uncoated asbestos-
cement roofing tiles and found an average release rate
of asbestos-cement fibers was 3 g/m2 per year. They
cited rainwater as the primary cause of releasing
While it may be possible that hail impacting eroded
asbestos-cement roofing can release fibers into the air,
this doesn't seem to be any more than by normal
weathering. We are not aware of any scientific studies
to date that would indicate that hail merely striking a
roof (and leaving spatter marks) causes damage to the
tile. Therefore, we currently do not consider asbestos-
cement tile as hail damaged unless it is fractured.
6.2 Other anomalies of asbestos-cement tiles
As mentioned previously, asbestos-cement tiles are
quite resistant to the effects of weathering. However,
the surface of the product provides a base for growing
algae, fungus, and lichens. Also, as the tile wears, it
may exhibit erosion of its surface layer as well as edge
delamination. These effects can be erroneously
attributed to hail damage. The tile also is susceptible to
foot traffic damage, especially at tile corners or in areas
where the tile is elevated and has less underlying
support. Recent fractures can be distinguished from
older fractures by the extent of discoloration on the
exposed fracture surfaces. Tiles broken recently exhibit
fresh, unweathered surfaces whereas tiles broken quite
some time ago usually are discolored with algae,
fungus, lichens, or dirt (Figure 18).
Figure 18. Non-hail caused anomalies on asbestos-
cement tiles: a) algae, b) erosion of coated tile, c) old
broken tile, and d) new broken tile corner from foot
A study has been conducted on the effects of hail on
various roofing tiles. In this paper, we presented test
results regarding ice ball impacts against clay,
concrete, wood-fiber cement, and asbestos-cement
roofing tiles. Ice balls of various sizes were propelled
at different tile targets by a specially designed
mechanical launcher. The velocities of the ice balls
were carefully monitored and recorded. Each of the
roofing products tested exhibited certain levels of
impact resistance. For example, ice balls of 1 in. (2.5
cm) in diameter or less resulted in no damage to any of
the tested roofing products. W e found the damage
threshold for most of the roofing products tested was
about 1.5 in. (3.8 cm) in diameter.
The characteristics of hail impact typically involved
breakage of the tile resulting in multiple irregular
fractures emanating from the impact point. However,
softer wood-fiber cement tiles were indented.
Generally, tile corners were more susceptible to
breakage than field portions of the tile by smaller ice
balls. Fractured tiles were considered as damaged.
We also presented examples of non-hail type
damage and anomalies to various roofing tiles
attributed to weathering, installation, and
manufacturing. This was done in an effort to aid
damage inspectors in distinguishing hail-caused
damage from other types of conditions.
The authors would like to thank C. Kirkpatrick, P.
Lawler, J. Stewart, and D. Teasdale for reviewing this
Bornemann, P. and U. Hildebrandt, 1986: On the
problem of environmental pollution by weathering
products of asbestos-cement. Staub Reinhalt Luft, 46
Hobson, V., 2001: Historic and Obsolete Roofing Tile,
Remai Publishing Co., Englewood, CO, 254 pp.
Greenfeld, Sidney H., 1969: Hail resistance of roofing
products, Building Science Series #23, National Bureau
of Standards, 9 pp.
Laurie, J.A.P., 1960: Hail and its effects on buildings,
Council for Scientific and Industrial Research, Report
No. 176, Pretoria, South Africa, 12 pp.
Koontz, Jim D., 1991: The effects of hail on residential
roofing products, Proc. of the Third International
Symposium on Roofing Technology, NRCA/NIST, 206-
Murphy, C., 2002: Blue-green algae and its effects on
fiber-cement roofing within a microclimate, Interface, 20
Spurny, K. R., 1989: On the release of asbestos fibers
from weathered and corroded asbestos cement
products, Environ. Res., 48, 100-116.