26 September 2006
CHAPTER 2 LOW SLOPE ROOFING DESIGN REQUIREMENTS
The NRCA Manual provides a wide range of information for design and construction of
low slope roofing assemblies. This chapter reinforces particularly salient information
with regard to military use or limits the applicability of certain techniques in the NRCA
Manual. Where contents of the NRCA Manual are acceptable without modification
those sections are not mentioned herein.
Prior to the specification of low slope roofing systems designers must analyze the life-
cycle costs associated with various low slope roof system alternatives. Designer shall
also refer to UFC 3-330-02A for roof selection criteria. Compliance with the appropriate
Unified Facilities Guide Specifications (UFGS) is mandatory.
Because of the wide variety of materials available and the variation in quality in similar
materials, design-build contracts for low slope roofing systems must name the specific
desired low slope roofing system (BUR, EPDM, etc.) and identify relevant performance
requirements to be provided under the contract. It is not sufficient to simply specify a
low slope roofing system per the NRCA Manual. Compliance with the appropriate
UFGS is mandatory.
GENERAL LOW SLOPE ROOFING CONSIDERATIONS.
Design all low slope roofs for a minimum temperature difference of 66 0 C (150 0 F).
Moisture Control Using a Vapor Retarder.
The designer must perform a dew point calculation to verify that the vapor retarder has
been positioned correctly in the roof assembly. Provide a moisture/ condensation
analysis in a project's design analysis based on the current version of ASHRAE
Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings
and Standard 90.2, Energy-Efficient Design of Low-Rise Residential Buildings. Care
must be taken to maintain the continuity of the roof vapor retarder, which is critical to its
performance. Moist air leakage through poorly installed vapor retarders defeats their
purpose and creates interior moisture problems.
The minimum slope for construction of new buildings is :12 to achieve positive