Science and Law of Hail Damage
WIND Regional Symposium SCIENCE AND LAW OF HAIL DAMAGE
SCIENCE HAIL And It s s Effects on Roofing Systems
Presented By:
HAIL FORMATION Hail is most commonly formed in frontal storms, where a cold, high air mass encounters a low moist air mass. Cooling the moist air causes water droplets to condense and freeze. Updrafts can lift ice masses repeatedly, accumulating layers of ice until they become too heavy and fall.
SIZE AND DISTRIBUTION Hailstones in any given storm are rarely of uniform size. Small to medium hail is usually spherical. Larger hailstones tend to have jagged edges which increases damage.
Hail size slide
Hail size slide
Lilburn, GA April 23, 2009
Lilburn, GA April 23, 2009
SPRING AND SUMMER 79% OF HAIL STORMS OCCUR IN FOUR MONTHS: MAY 18% JUNE 24% JULY 21% AUGUST 16%
SIZE AND DISTRIBUTION Minimum size is 0.2 to be classified as hail.25 is referred to as pea-size Largest hailstone recovered in the US fell in Aurora, NE on June 22, 2003 7 in diameter 18.75 in circumference (NOAA National Severe Storms Laboratory)
Distribution Hail typically falls in paths known as hail swaths Swaths can range in size from a few acres to areas 10 miles wide and 100 miles long (NOAA National Severe Storms Laboratory)
Size Pea ¼ diameter Marble ½ Dime / Penny -= ¾ Nickel 7/8 Quarter 1 Ping Pong Ball 1 ½ Golf Ball 1 ¾ Tennis Ball 2 ½ Baseball 2 ¾ Tea cup 3 Grapefruit 4 Softball 4 ½
DAMAGE DEPENDS ON IMPACT ENERGY K.E. = wv 2 / 2g w = weight of hailstone V = terminal velocity of the hailstone g = acceleration of gravity
FREE FALLING HAILSTONES SIZE (IN) WEIGHT (LB) VELOCITY (MPH) ENERGY (FT-LB) 1/2 ¾ 1 1 1/4 1 ½ 1 ¾ 2 3 0.002 0.007 0.017 0.034 0.058 0.093 0.138 0.467 34.7 42.3 49.8 55.9 61.4 66.2 71.6 88.6 0.09 0.44 1.43 3.53 7.35 13.56 23.71 122.66
TERMINAL VELOCITIES AND IMPACT ENERGY OF VARIOUS SIZE HAILSTONES 140 120 100 80 60 40 TERMINAL VELOCITY (mph) IMPACT ENERGY (ft-lbs) 20 0 0.5 1 1.5 2 4
SIMULATED HAIL TESTING Testing based on matching impact energy of free fall hailstones Used molded ice balls shot from compressed air guns. Only tested perpendicular impacts on new shingles 1969 test data (National Bureau of Standards) is for organic felt shingles
SIMULATED HAIL TESTING More recent testing (Haag Engineering and others) included de- saturating the shingles to determine mat condition. Threshold sizes for damage determined Testing still limited to perpendicular impact on new shingles.
IMPACT TESTS FOR LOW SLOPE SYSTEMS FACTORY MUTUAL 4470 MODERATE HAIL 1 ¾ STEEL BALL DROPPED 5 FEET ENERGY APPROXIMATES 1 ½ HAIL SEVERE HAIL 2 STEEL BALL DROPPED 17-9 9 1/2 ENERGY APPROXIMATES 1 ¾ HAIL
IMPACT TESTS FOR LOW SLOPE SYSTEMS SWISS TEST METHODS USES 40 MM PLASTIC BALLS SHOT FROM AIR GUNS
IMPACT TESTS FOR LOW SLOPE SYSTEMS UNDERWRITERS LABORATORIES TEST STEEL BALLS OF VARIOUS SIZES DROPPED FROM VARIOUS HEIGHTS
IMPACT TESTS FOR SHINGLES UL 2218 DEVELOPED IN 1996 ESTABLISHES 4 CLASSES OF IMPACT RESISTANCE FOR SHINGLES USES STEEL BALLS FALLING VARIOUS DISTANCES SHINGLES MUST SURVIVE DOUBLE HIT IN SAME SPOT
UL 2218 IMPACT TEST CLASS 1 CLASS 2 CLASS 3 CLASS 4 BALL SIZE 1 ¼ 1 ½ 1 ¾ 2 DROP HEIGHT (FEET) 12 15 17 20
FM 4473 USES FREEZER ICE BALLS IMPACT TESTING FOR RIGID ROOFING MATERIALS (SLATE, CONCRETE, CLAY)
FM 4493 CLASSIFICATION CLASS 1 CLASS 2 CLASS 3 CLASS 4 FREEZER BALL SIZE 1 ¼ 1 ½ 1 ¾ 2 KINETIC ENERGY (ft-lb) 3.72 7.77 14.95 26.81 Pass/Fail Criteria: No visible cracking or breakage after two impacts at same location
WHAT IS DAMAGE? Functional Damage To Roofing Diminishment of water-shedding capability Reduction in the expected long- term service life. (From Hail and Composition Shingles,, Haag Engineering, 1993)
WHAT IS DAMAGE? SEVERE DAMAGE Damage which leads to penetration of the building by the elements. SUPERFICIAL DAMAGE Damage which affects the appearance but does not materially interfere with the performance of the roofing. (From Hail Resistance of Roofing Products NBS, 1969)
EVALUATING HAIL DAMAGE HAIL IS RANDOM! SIZE VARIES DISTRIBUTION VARIES HARDNESS VARIES SHAPE VARIES EFFECTS VARY
ENVIRONMENTAL CONDITIONS LESS DAMAGE OCCURS ON STEEP SLOPES MORE DAMAGE OCCURS ON WINDWARD SLOPE WIND CAN INCREASE IMPACT VELOCITY AND DAMAGE
WIND AFFECTS IMPACT ANGLE
ROOF SLOPE AFFECTS IMPACT ANGLE
ROOF CONDITIONS AGE OF THE SHINGLES OLDER SHINGLES ARE MORE PRONE TO IMPACT DAMAGE VENTILATION POOR VENTILATION ACCELERATES AGING OF SHINGLES TYPE OF SHINGLE HEAVIER WEIGHT SHINGLES ARE MORE HAIL RESISTANT AGED ORGANIC FELT BASED SHINGLES ARE VERY SUSCEPTIBLE TO IMPACT DAMAGE
ROOF CONDITIONS EXPOSURE SHELTERING TREES REDUCE IMPACT SUN / SHADE AFFECTS HEAT OF SHINGLES DARKER SHINGLES ABSORB MORE HEAT FOOT TRAFFIC INSTALLATION DAMAGE TOE BOARDS / SCUFFS PAINTING MAINTENANCE ROOF INSPECTIONS
ROOF CONDITIONS SUPPORT FOR SHINGLES UNDERLYING LAYERS OF OLD SHINGLES RAFTER SPACING ROOF DECKING FELT UNDERLAYMENT
WHERE DOES DAMAGE OCCUR? IMPACT DAMAGE IS MOST LIKELY TO OCCUR WHERE SHINGLES HAVE LEAST SUPPORT VALLEYS RIDGES TAB CUTOUTS EDGES CORNERS
RECENT IMPACT MARK
IMPACT MARK ON RIDGE SHINGLE
IMPACT MARK ON RIDGE
IMPACT ON EDGE OF SHINGLE
WEATHERED IMPACT MARK AT EDGE
IMPACT MARK AT SHINGLE EDGE
HAIL SIZE REQUIRED FOR POSSIBLE DAMAGE Heavy Composition Shingles - 1 ¼ Lightweight Shingles - 1 Deteriorated Shingles ¾ (Nebraska Department of Insurance)
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) ½ Few if any roofs damaged. Leaves stripped from bushes and trees. Thin aluminum vents, fins on air conditioning units, lead sleeves on soil stacks, window screens, and aluminum awnings dented.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) ¾ Threshold size for damage to roll roofing and deteriorated composition shingles, especially where unsupported. Painted wood surfaces chipped; most aluminum vents, flashings, valleys, and siding dented.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) 1 Threshold size for damage to most lightweight composition shingles. Single pane windows and thin skylight shells cracked or broken.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) 1 ¼ ¼ Threshold size for damage to most heavy composition shingles, wood shingles, and older medium shakes. Automobile body metal dented, and (rarely) windshields cracked Galvanized metal vents dented.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) 1 ½ ½ Threshold size for damage to clay tile, slate, and new medium shakes. Serious denting of automobile body metal.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) 1 ¾ ¾ Threshold size for damage to new heavy shakes. Metal vents caved in. Bare spots on built up roofs bruised or punctured.
TYPICAL DAMAGE (From: Hail and Composition Shingles, Haag Engineering Co.) 2 Threshold size for damage to new jumbo shakes, most concrete tile, and unballasted built-up up roofing on flexible underlayment.
SHINGLE DAMAGE (From: Hail Resistance in Roofing Products, NBS) 2 MINIMUM SIZE HAIL REQUIRED FOR FAILURE ON TAB EDGES OR UNSUPPORTED AREAS.
GRANULE LOSS SHINGLES CONSTANTLY SHED GRANULES 75% OF GRANULES ARE WELL BONDED TO NEW SHINGLES 25% ARE NOT 10 TO 15 OZ OF GRANULES PER SHINGLES
GRANULE LOSS A TYPICAL ROOF WITH 30 SQUARES OF SHINGLES HAS ABOUT 2200 POUNDS OF GRANULES 10 POUNDS OF GRANULES IN THE GUTTERS IS LESS THAN ½% % OF THE TOTAL WEIGHT OF GRANULES
GRANULE LOSS FOR A 20 YEAR SHINGLE ROOF, LOSS OF 1/2 % % OF THE GRANULES MAY SHORTEN THE USEFUL LIFE OF THE ROOF BY ABOUT A MONTH. ASSUMES A DIRECT CORRELATION BETWEEN GRANULE LOSS AND SHINGLE LIFE.
WHAT ISN T T HAIL DAMAGE LEAKS (USUALLY) TOE BOARD HOLES NAILS BACKING OUT OF DECK SCUFFS BLISTERS FOOT TRAFFIC LADDER DAMAGE INSTALLATION DAMAGE
FRACTURE AT RIDGE
PIPE BOOT
SCUFFS ABOVE BOARD LOCATION TOE BOARD HOLE
SHINGLES LIFTED BY STAPLES BACKING OUT OF DECK
STAPLE BACKING OUT OF DECK
PROTRUDING DECKING NAIL
SCUFFS FROM FOOT TRAFFIC
WIND DAMAGE
SCUFFS ALONG WALL
WEATHERED IMPACT MARKS
CRACKS FROM HEAT AND AGE CATHEDRAL CEILING BELOW
BLISTER IMPACT MARK ON HEAT AFFECTED SHINGLE
HAIL CLEANING OF ALGAE STAINS
IMPACT MARKS
CODE CONSIDERATIONS VENTILATION R806.2 Minimum area. (2006 IRC) The total net free ventilating area shall not be less than 1/150 of the area of the space ventilated except that reduction of the total tal area to 1/300 is permitted, provided that at least 50 percent and not more than 80 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above the eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents. As an alternative, the net free cross-ventilation area may be reduced to 1/300 when a vapor barrier having a transmission rate not exceeding 1 perm (5.7 10-11 11 kg/s m2 Pa) is installed on the warm-in in-winter side of the ceiling.
CODE CONSIDERATIONS R907.3 Re-covering versus replacement. (2006 IRC) New roof coverings shall not be installed without first removing existing roof coverings where any of the following conditions occur: cur: 1. Where the existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering g is not adequate as a base for additional roofing. 2. Where the existing roof covering is wood shake, slate, clay, cement ent or asbestos-cement tile. 3. Where the existing roof has two or more applications of any type of roof covering. 4. For asphalt shingles, when the building is located in an area subject to moderate or severe hail exposure according to Figure R903.5.
CODE CONSIDERATIONS R903.5.1 Moderate hail exposure. One or more hail days with hail diameters larger than 1.5 inches (38 mm) in a 20-year period. R903.5.2 Severe hail exposure. One or more hail days with hail diameters larger than or equal to 2.0 inches (51 mm) in a 20-year period.
MODERATE HAIL REGION 2006 IRC
SUMMARY OF KEY POINTS HAIL AND HAIL DAMAGE TO SHINGLES IS HIGHLY VARIABLE DAMAGE IS MORE LIKELY ON LOWER SLOPED ROOFS DAMAGE IS MORE LIKELY ON POORLY SUPPORTED AREAS NEW ROOFS ARE MORE HAIL RESISTANT THAN OLD ROOFS
SUMMARY OF KEY POINTS DENTS IN METAL VENT COVERS DO NOT MEAN THE SHINGLES ARE DAMAGED MINOR TO MODERATE GRANULE LOSS DOES NOT SIGNIFICANTLY AFFECT THE LIFE OF THE SHINGLE