www.mrca.org  —  Midwest Roofer
38
Introduction
Wiss, Janney, 
Elstner 
Associates, Inc. 
(WJE) and the 
Midwest Roofing 
Contractors Association (MRCA) Technical and 
Research (T&R) Committee have a history of 
collaborating to develop research and testing 
programs that focus on expanding knowledge 
of commonly used roofing materials. In 2023, 
the focus of the research and testing was on 
granule-surfaced, modified bitumen roofing 
membranes. WJE, in collaboration with the MRCA 
T&R Committee, developed a testing program to 
evaluate the influence of hail impact on granule-
surfaced modified bitumen roof membranes 
installed in a low-slope roof assembly. The 
objective of the test program was to determine 
the extent of damage to these membranes from 
a single manufacturer of various ages through 
physical testing and laboratory review and 
analysis. 
Test Program Description
Testing was conducted in accordance with 
ASTM D3746, Standard Test Method for Impact 
Resistance of Bituminous Roofing Systems. Per 
the standard, “this test method subjects 305 by 305 
mm [12 by 12-in.] specimens of a roofing system 
(insulation and membrane complete with top 
surfacing) to a series of four impacts, one in each 
quadrant, from a standard missile falling freely 
from a predetermined height with an impact energy 
of 30.0 J [22 lbf-ft]. Damage to the membrane is 
assessed by visual examination of the felts after 
solvent extraction of the bitumen.” 
Eighteen 12-inch by 12-inch samples were divided 
into four 6-inch by 6-inch quadrants. A 5-pound, 
2-inch diameter steel missile was released from 
By Heidi Mase and Richard Koziol of Wiss, Janney, Elstner Associates, Inc.
TECHNICAL & RESEARCH
HAIL IMPACT TESTING OF MODIFIED 
BITUMEN ROOF MEMBRANES 
BITEC Photo

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