Although hailstorms generally are seen as a regional and seasonal problem, the Hail Belt area of the U.S. appears to be getting larger, according to research from the National Oceanic and Atmospheric Administration’s (NOAA’s) National Severe Storms Laboratory. Areas of the U.S. that were not particularly vulnerable to hailstorms now are receiving hail, and areas that regularly received hailstorms are seeing more storms with larger hail.
Just within the past year alone (2112), North Texas has sustained an immense amount of hail damage to both residential and commercial roofs leading to over $2 Billion in property claims according to Southwest Insurance Service. In most cases, slope and conventional shingled roofs are fairly easy on the visible surface to identify. However, it gets a little more complicated when evaluating the damages to low slope and flat roof systems. There are many variables that must be taken into consideration as a roof is inspected for hail damage. The first thing to establish is to identify the roof system– Built-up (BUR), Spray Polyurethane Foam (SPF), Modified bitumen (Mod-bit), Polyvinyl Chloride (PVC), Ethylene Propylene Diene Monomer (EPDM) or Thermoplastic Polyolefin (TPO) membrane systems. The next step is to identify the actual hailstone size as reported in the affected areas. Generally, anything greater than 3/4 of an inch in diameter has been considered the minimum threshold for property damage by industry professionals and government entities, such as the National Severe Storms Laboratory. However, in January 2010, the NOAA/National Weather Service issued a proclamation that the criteria for a severe storm has changed from ¾ inch (the size of a penny) diameter hailstone to 1inch (the size of a quarter). So why the change? There were really two motivating drivers: Scientific research indicates that significant damage to real property such as roofing materials does not occur until hailstones reach at least 1inch in diameter. The results of these peer-reviewed articles are supported by damage reports from thousands of archived storm events. Secondly, media partners and the emergency management community expressed concern about the numerous warnings being issued for marginal events – that is, storms which may well produce hail in the penny or nickel size range, but are not expected to pose any substantive threat to property. Their concern was that these warnings were desensitizing the public to those events where there is a genuine risk of damage and a corresponding need to take protective action. This makes roof protection against hail damage an even greater priority now. Combined with an inconsistent procedural standard by which (all) hail damage is measured, building owners will run an even greater risk when undetected surface deterioration takes place over long term periods– chemical breakdown of material properties will eventually lead to a failing roof system over time. Sometimes the undetected impact of hail takes years to become an apparent issue to the longevity of a roof. Given the escalating cost of materials and construction, building owners often face higher costs for repairs or replacements necessitated by hail damage, not to mention the impact of water intrusion that creates damage to equipment, inventory and other miscellaneous property within the dwelling.
Research indicates that there are definite pros and cons for some of the various roofing systems. Although it is clear these materials perform in a more than acceptable fashion in most circumstances, they sometimes struggle to maintain their protective qualities when facing significant hail fall.
Regardless of whether a built-up roof (BUR) system is coal-tar pitch or asphalt, gravel-surfaced BUR systems are somewhat less likely to be hail-damaged than smooth-surfaced BUR systems because gravel disperses hail’s impact energy. But when damage occurs, it can be more difficult to pinpoint. When a BUR system is damaged by hail, the asphalt or pitch is displaced or cracked at the surface and the fiberglass felt may fracture, allowing water infiltration and the beginnings of premature roof system deterioration.
Water infiltration into the insulation may spread and what began as a small puncture may become a large repair. Multiple hail blemishes may require tear-off and reroofing as the only practical remedy.
Spray polyurethane foam (SPF) roof systems are popular in some areas where hailstorms are becoming more frequent. Although the foam in these roof systems is closed-cell and may not leak immediately after hail damage, the required repairs to this type of roof system can be costly and fractures can be particularly difficult to find on some of the newer granule-surfaced systems. However, hail damage on SPF roof systems can be repaired unless the number of hail fractures is large, which then may require tear-off and reroofing or at least scarifying of the surface and recoating.
Modified bitumen roof systems provide good service when applied correctly in the appropriate situation. In addition, modified bitumen roof systems typically are more hail-resistant than smooth-surfaced BUR systems, but other factors come into play. For example, an APP membrane is modified with plastic and, as a result, is less flexible than rubber. This makes it somewhat vulnerable to hail fractures. SBS membranes are modified with a type of rubber that is vulnerable to ultraviolet degradation. Because of this, SBS-modified bitumen membranes are protected by a granule surface, which may be displaced by hail.
Even though a membrane may not fracture, it would require replacement or repair because of the granule displacement. Both APP- and SBS-modified membrane systems can be damaged by hail because they are asphaltic products.
PVC roof membranes have become more popular during the past 25 years, and each PVC membrane manufacturer has its own slightly different recipe for its PVC product. There are differences in the added ingredients used in various PVC membranes, particularly the plasticizers. Because PVC is rigid in its natural state, the process of making it into a flexible single-ply roof membrane requires the addition of plasticizer chemicals. Some manufacturers use liquid; others use solid plasticizers.
The type of plasticizer used can make a great difference in whether a membrane becomes brittle as it ages and, as a result, more vulnerable to hail damage. A PVC membrane is typically reinforced with a polyester fabric, but some of the older types are not. Here are examples of both types, reinforced and non-reinforced. The circular fractures eventually transfer through the membrane and develop into leaks. (photos featured here)
Over prolonged periods of time, in this case three years after the initial hail storm, more and more stress fractures begin to appear requiring repeated surface caulking repairs until virtually the roof becomes and huge liability. It is virtually impossible to prevent the roof from opening and leaking grows beyond control. (more photos)
EPDM roof systems can be installed using one of three basic methods. The least expensive is to simply lay the membrane loose over the insulation substrate and cover it with rock ballast to prevent blow-off. Based on the region of the country and inherent wind and weather conditions should determine the most appropriate scope and method of installation.
The second method is to mechanically fasten the membrane at intervals on the roof and cover the attachment fasteners with EPDM cover-strip material or overlapping seams. The third method is to fully adhere the membrane to the substrate. A ballasted system may perform somewhat better during a hailstorm because the rock ballast absorbs the energy of the hail. But in general, performance of EPDM against hail damage is consistent regardless of installation method.
EPDM membranes are available in 45-, 60- and 90-mil thicknesses. The 90-mil membrane offers higher resistance against damage from hail or other punctures. Ice balls have been used to simulate hail impact on roof system test decks. The tests show ultimate failure of the thinner 45-mil membrane when hit by a 3-inch-diameter ice ball at 133.2 feet per second, or more than 90 miles per hour.
These are just a few key things to consider as you evaluate the conditions of your roof after a hailstorm. Based on weather cycle history and forecast, there is no doubt that North Texas and surrounding states will continue to feel the effects of hail well into the future. LSR works with a variety of forensic roof consultancies in helping to identify sustained hail damages. We encourage building owners that are in the process of evaluating their roofs and possibly replacing them with new systems to carefully weigh the pros and cons of the various types available today. Always consider the systems ability to sustain long-term performance, roofing material that holds up against hail, effective installation, maintenance requirements and inspection methods required for each roofing system option.