www.mrca.org  —  Midwest Roofer
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mall details can have 
an enormous impact. 
Get them right, and the 
likelihood of success can increase 
exponentially. Get them wrong, 
and the results can be disastrous. 
This is certainly true in low-slope roofing. The 
details—from drainage to penetrations and edge 
metal—are essential to ensuring a roof’s long-term 
durability and performance. They are, however, 
also the source of the vast majority of roofing-
related issues.
Some of these issues are, of course, the result 
of poor workmanship by the roofing contractor. 
Most, however, stem from improper roof design or 
specifying the wrong products for the job. 
This article will outline seven points that, if kept 
in mind during the design process, can eliminate 
many roofing-related change orders and reduce 
installation time and costs.
Water MUST Leave the Roof
The following cannot be stated often or strongly 
enough: water MUST leave the roof AT ANY COST.
There are three ways to achieve the necessary 
slope to accomplish the goal: structural slope, 
tapered insulation, or a combination of tapered 
steel and tapered polyisocyanurate crickets.
Tapering structural steel is the least costly method 
and is generally used in new construction. Adding 
slope of 1/4-inch per foot to a 40-foot-by-40-foot 
span requires only a 10-inch difference in the grid 
line of the columns and lengthening the joists by 
1/8-inch. 
Using tapered insulation to accomplish the same 
task would require an additional 8,400 board feet 
of tapered insulation and, if mechanically fastening 
the insulation, fasteners in three different lengths. 
At today’s prices, this would add approximately 
$13,000 to the project’s cost.
By Jim Flickinger
TECHNICAL & RESEARCH
AVOIDING COMMON LOW-SLOPE 
ROOF DESIGN PROBLEMS

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