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Re: Roof Design Components and Cladding or MWFRS - ASCE7-02

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The ASCE-7 Standard is silent as to what specific structural elements are C&C and which are MWFRS.  It is necessary for the engineer to apply the definitions of the Standard and determine what structural elements require C&C loading and which require MWRS pressures. For guidance in making this determination I refer to the following scholarly publications.


ASCE 7-98 Commentary, p243

ASCE 7-02 Commentary, p271

Guide to the Use of the Wind Load Provisions of ASCE 7-98, FAQ #1 (Kishor Mehta)

Guide to the Use of the Wind Load Provisions of ASCE 7-02, FAQ #16 (Kishor Mehta)

SBCCI Guide to Concrete Masonry Residential Construction in High Wind Areas, p1.5

AF&PA Wood Frame Construction Manual for One and Two Family Dwellings 1.3 & Commentary 1.1.2

AF&PA Considerations in Wind Design of Wood Structures (Douglas, Weeks)

WTCA Metal Plate Connected Wood Truss Handbook, p6-5


These publications clearly permit engineering judgment.


Kishor’s Guide (02) recognizes the common practice of designing different parts of the truss for different types of loads.


The ASCE-7 Commentary does not imply that trusses are always C&C, but only examples of elements that can be C&C.


I believe a careful application of the C&C and MWFRS definitions in the Standard clarifies the issue of how to design trusses.


Christopher Banbury, PE


Ark Engineering, Incorporated

PO Box 10129, Brooksville, FL 34603-0129

22 North Broad ST, Brooksville, FL 34601

352.754.2424 (o)

352.754.2412 (f)