REVIEWED BLD BLD2021-0580+Calculations+4.22.2021_3.14.59_PM+2159713Calculations for Extended Deck
18" X 18" X 12" footing on soil bearing at least 2000 p.s.f. = 4500 pounds allowable per
footing.
The largest attributable area on my deck is 49.5 square feet. 4500 divided by 49.5 = 90.9 p.s.f.
The longest beam span I have is 10' Using Span Chart provided by Humbolt Redwood, that
span using #2 fir will support 250 p.l.f. or 2500 pounds evenly loaded. Again using the largest
attributable area on my deck 49.5 square feet. 2500 divided by 49.5 = 50.5 p.s.f.
For the joists, using the chart in the 2018 International Residential code Deck joist spans, my
longest joist is 8', two feet of which is cantilevered. The chart states the maximum span is
11'1" using 16" centers and a 2'1" cantilever for a total 50 p.s.f. load. (10 p.s.f. dead and 40
p.s.f. live and snow load.)
So my new deck is good to a minimum of 50 p.s.f.