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The bottom chord of a truss is typically designed as a tension tie. Note the several splices along its length. It is usually not intended to support weights bearing downward on the bottom chord directly -- the primary function of the truss is to support loads on top of the roof, not point loads on individual members. That said, many designs include a budget for an incidental ceiling load -- say 5 to 10 pounds per square foot. This is especially true if the trusses were spaced 2 feet or less on center. And a truss design that could not handle a workman stepping from chord to chord would probably not be a realistic one, even if it could support the theoretical roof load. If the building uses 8 foot spacing of "king" trusses, and purlins for the roof support, then the "ceiling" statement wouldn't apply -- but then again the members are so beefy in that case that a 150 pound incidental load would likely fall within the design safety factor. Hanging the canoe near the wall is a fairly safe place. This will put much less bending moment on the bottom chord of the truss than hanging it from the center of the truss. Ideally, your hangers should rest on TOP of the truss chord. Remember that wood has NO allowable design value for tension across the grain. So drilling holes through the side or bottom of the truss chord not only reduces its cross section (and thus its ability to act as a tension tie), but the hanging weight will load the wood in a direction that tends to split it.
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