www.mrca.org  —  Midwest Roofer
18
A
s many building restoration 
consultants and contractors 
will attest, the design and 
construction of roof replacements 
have evolved substantially over the 
last 20 years. Contractors and roof 
designers can no longer rely on habitually selecting 
favorite roof solutions, and one roof system or assembly 
can no longer be considered suitable for all buildings. 
There is no longer one material manufacturer that 
can supply all the solutions. New roof designs have 
increased demands from building owners for roofs that 
offer complete sustainable solutions, not just waterproof 
protection. 
Evolution of roof construction practices
Roof construction in the mid-’80s was a predictable 
practice. Roofing crews would leave their place of 
business to work on projects where the only installation 
instruction required was the amount of roof work 
expected to be completed that day. There was no 
question of what type of roof system was to be installed, 
no concern about how much or what kind of insulation 
was required, and no consideration of how to ensure 
continuity of the air barrier, vapor retarder, tie-ins, 
adhesive rates, mechanical fastening patterns, material 
lists, or shop drawings. The practice proved effective, 
with roofing contractors installing watertight solutions 
that typically provided long-lasting, effective results. 
Roofing technicians were craftsmen often trained 
through apprenticeships and generational-type training. 
They were successful in their trade primarily due to the 
predictable and repetitive nature of working with built-up 
roof assemblies, which had few variables and a sole 
objective: keeping precipitation out. There was very 
little consideration given to using roof assemblies for 
anything other than waterproofing.
Modern construction practices and increased 
By Michael Hensen P.Eng. RRC
TECHNICAL & RESEARCH
BUILDING SCIENCE 
ON ROOFING:
BARRIERS GUIDE MODERN DESIGN
Photos By Chris Dawson

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