Can you give me the load limit on a 4x6 pine board 18' long used for a swing set? Thank you
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Assuming it’s “Lodgepole Pine” (Idaho Pine and Ponderosa Pine is slightly less) and it’s grade is a No. 2 and better (no loose or missing knotholes), then a 4x6 spanning 18’ will support about 105 lbs. loaded at the mid-span (slightly higher if it’s loaded at third points or further from the center point).
Better idea instead of the 4x6 use 2 2x8 boards bolted of nailed together. Ive done this on a 18 foot span and it holds 3 large adults (over 200 lbs each) on swings without any flex or bowing. Outdoors i would use a good grade of treated lumber to prevent decay from the elements and longer life.