TECHNICAL
www.mrca.org  —  Midwest Roofer
12
P
ost-frame construction is continuing to expand 
its footprint. Part of this expansion involves 
much larger structures than was common just 
a few years ago. Improved materials and expanded 
design knowledge have helped to increase the number 
and size of these larger structures. Post frame can now 
handle building widths well over 100’ wide, and heights 
of 20’ or more at the eave are possible. Even in this size 
range, post frame can provide a structure that meets 
even the strictest design criteria, at a cost that is very 
competitive relative to other types of construction.
One of the design considerations now getting increased 
attention is how to effectively use traditional, exposed-
fastener metal roofing panels in these large structure 
applications. Multiple panels are needed to reach from 
eave to ridge, creating the need for panel endlaps. 
When all aspects of the roof system design and 
installation are not carefully considered, these large 
structures can develop weathertightness concerns at 
the roof panel endlaps and other areas. The building’s 
contents, as well as the structure itself, can be damaged 
when moisture is allowed to get past the roof system 
and enter the building.
Leaking roof systems are not acceptable. Roof system 
“movement,” for example, can overload panel endlaps 
and cause them to become compromised over time, 
resulting in moisture getting past these panel endlaps. 
There are several load cases that generate the forces 
known to cause roof system movement. Currently, there 
are only a few known effective solutions to prevent 
and repair post-frame panel endlaps and other areas 
that become compromised. Differences in building 
design and construction (i.e., truss roof system vs. 
post and beam roof system), differences in building 
materials (i.e., 100 percent aluminum vs. steel roofing), 
etc., make a universal solution difficult. However, with 
a better understanding of roof system movement, 
effective panel endlap designs and other solutions 
can be identified to allow the roof system to remain 
weathertight over its life span.
The focus of this article is the roof panel endlap, 
recognizing that other areas of the roof system can also 
experience damage (i.e., other shear transfer areas, 
etc.). More work needs to be done to understand roof 
system movement and the interaction between the 
various roof system components. Over the past several 
years, Rigidply Rafters Inc. has investigated numerous 
projects, has viewed their roof system weathertightness 
By: Kenneth J. Guffey, PE
KEEPING LONG-SPAN ROOFING 
WEATHERTIGHT

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