26 September 2006
CHAPTER 3 STEEP SLOPE ROOFING DESIGN REQUIREMENTS
Steep slope roofing systems provide excellent performance and long service life.
However, these roofing systems require structural supports that may become
prohibitively expensive for large buildings. When considering the use of steep slope
roofing systems, compare the cost with the cost of low slope systems. Cost
comparisons should include maintenance as well as the cost of the roof and structure.
Very steep sloped roofs present additional safety and maintenance issues that must be
Chapter 3 limits the applicability of certain techniques permitted by the NRCA to focus
on long life cycle military requirements. Where contents of the NRCA Manual are
acceptable without modification, those sections are not mentioned.
Prior to specifying steep slope roofing systems, analyze the life-cycle costs of the
various systems, and refer to UFC 3-330-02A for additional selection considerations.
Compliance with the appropriate UFGS is mandatory.
Because of the wide variety of materials available and the variation in quality in similar
materials, design-build contracts for steep slope roof systems must name the specific
roofing material desired and identify relevant performance requirements to be provided
under the contract. It is not sufficient to simply require a steep roof system per the
NRCA Manual. Compliance with the appropriate UFGS is mandatory.
GENERAL STEEP ROOFING CONSIDERATIONS.
All metal roofs must be designed for a temperature difference (Delta T) of 93 0 C (200 0
F). All other roofs must be designed for a temperature difference of 66 0 C (150 0 F).
Moisture Control Vapor Retarder.
The designer must perform a dew point calculation to verify that a vapor retarder is
needed, and if needed, it has been positioned correctly in the roof assembly. A
moisture/ condensation analysis must be provided in a project's design analysis based
on the current version of ASHRAE Standard 90.1 and Standard 90.2.
Provide crickets on the up-slope side of all non-round penetrations on steep slope roofs.
Curbs must be high enough to not void the roof system warranty, but shall not be less
than 100 mm (4 in.) above the high point of a cricket.