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[SEAOC] Re: [SEAOC] Re: [SEAOC] Basic Roof Rafter Analysis Question

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I don't have a City of Los Angeles Type V sheet but do have the city's
Guideline 12 - Unit Weights of Building Materials. The issue is not if the
load conforms with the city's guidelines, but rather if the rafter can be
calculated for to work with the required load.
First, let me remind you that the intended tile is not a heavy (10 psf +)
tile, but rather a 7.0 psf maximum lightweight composite tile. 
According to the Guideline 12, cedar shake is good for 5 to 6 psf of dead
load. 1x skipped sheathing is approximately 1.0 psf -giving a total of 7.0
above the rafter.
1/2" plywood plus a 7.0 psf tile will place the new load at 8.5 psf.

My decision on this project was to add struts or brace the existing struts
to secure a positive reaction at the location of the purlin (backbrace or
perpendicular support). The rafter was then checked as a two span rafter
and the reaction of the struts was verified to be transferred to an
interior bearing wall.
Lateral was not a consideration here since the increased weight would not
change to a seismic governing force.

Dennis

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