ABSTRACT
Defects ..................................................................................................................... 131 4.4.3 Mod-Bit Thresholds for Hail-Strike Damage ..................................................... 133 4.4.4 Mod-Bit Inspection Case Studies ......................................................................... 133
4.4.4.1 Small Hail to Re—ective-Coated Mod-Bit Membrane ........................ 133 4.4.4.2 Large Hail to Gravel-Surfaced Membrane .......................................... 134 4.4.4.3 Large Hail to Smooth-Surfaced Re—ective-Coated Mod-Bit ............. 135
4.5 Ethylene Propylene Diene Monomer Roof Systems...................................................... 136 4.5.1 Description .............................................................................................................. 136 4.5.2 EPDM Membrane Roof Life and Commonly Encountered Surface Defects .......137 4.5.3 EPDM Thresholds for Hail-Strike Damage........................................................ 140 4.5.4 EPDM Inspection Case Study .............................................................................. 140
4.6 Thermoplastic Roof Systems ............................................................................................ 142 4.6.1 Description .............................................................................................................. 142 4.6.2 Thermoplastic Membrane Roof Life and Commonly Encountered
Surface Defects ....................................................................................................... 143 4.6.3 Thermoplastic Membrane Roof Surfaces: Thresholds for Hail-Strike
Damage .................................................................................................................... 143 4.6.4 Thermoplastic Inspection Case Studies ............................................................. 143
4.6.4.1 Hail-Strike Damage to Aged PVC Membrane .................................... 143 4.6.4.2 Hail-Strike Damage to Newer PVC Membrane .................................. 146
4.7 Metal Roof Systems ........................................................................................................... 147 4.7.1 Description .............................................................................................................. 147
By deˆnition, low-sloped roof systems consist of a category of roofs that are installed on slopes at a 3:12 or less pitch. Many commercial buildings (and portions of some residential buildings) throughout the United States have —at or low-sloped roof systems. A couple of major differences between commercial low-sloped roof systems and residential steepsloped roof systems are (1) the higher cost of removal and replacement and (2) the typical greater surface area of commercial low-sloped roofs. As with steep-sloped roof surfaces, commercial low-sloped roof systems are susceptible
to hail-strike damage. It is not uncommon for the replacement cost of a commercial lowsloped roof system to be 10 times greater (i.e., $100,000 vs. $10,000) than the replacement cost of a steep-sloped roof system.
