TECHNICAL & RESEARCH
building code demands have undergone substantial 
transformations since the 1980s, primarily to provide 
better environmental separation between interior and 
exterior climates, enhance interior comfort, and reduce 
energy costs. There are no longer umbrella-type covers 
on buildings; instead, there are impermeable solutions 
that attempt to control or eliminate thermal, moisture, 
and airflow migration. Early attempts with what seemed 
to be revolutionary materials, including new membranes 
and insulation designed to provide improved roof 
performance, brought mixed results. Roofers and 
designers alike experienced roof system failures, often 
due to a lack of understanding regarding the installation 
of roofs using new products and a lack of knowledge 
about the application of building science principles to 
roofing design and installations.
Challenges with early insulated roof systems
The early versions of insulated roof systems introduced 
new issues, including vapor drive and thermal bridging, 
which led to uncontrolled deterioration and premature 
failures of roofs, making them unable to provide the 
desired improved protection. The moisture-related 
deterioration included a reduction in anticipated thermal 
resistance values, mysterious leaks, emulsifying 
adhesives, metal corrosion, and mold issues. 
Membrane technology also changed as new membrane 
types were developed to improve performance and 
(hopefully) provide reliability in an insulated roof system. 
Roof membrane system types included single- and 
multi-ply assemblies incorporated in built-up (membrane 
over insulation) or inverted (membrane under insulation) 
formats. The unfortunate part of the new membrane 
and insulation trend was that the roofing industry was 
unsure about how to install and detail the new roof 
assemblies. Roofing contractors would rely on their 
workers, who had traditional built-up roof training, 
habits, and equipment, to install new single- or multi-ply 
systems by trial and error. As time progressed, some 
membrane manufacturers collaborated with contractors 
and industry organizations to develop best practice 
methodologies and achieve reasonable confidence in 
providing long-term solutions.
There is no denying that historically, owner roof 
replacement decisions were often swayed by selecting 
roof membrane systems from persuasive material sales 
staff offering extraordinary solutions and services, the 
attempt to save money by choosing an inexpensive 
solution, price, or choosing what appeared to be a too-
good-to-be-true warranty. The bottom line is no sales 
pitch can guarantee success, the best price does not 
ensure a successful solution, and no warranty has ever 
improved the performance of a roof assembly. A well-
Cold process modified bitumen membrane built-
up roof installation. 
www.mrca.org  —  Midwest Roofer
19
Thermo-fused modified bitumen 
membrane built-up roof replacement. 
Continued on page 20

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