3

The deck construction guide for my area contains this table:

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Look at the "Allowable Overhang" columns. It's odd that a wider joint spacing (24") permits a longer overhang.

For example, look at the row for 2x12 fir joists. At 12" O.C. spacing, overhang can be 4'4". At 24" spacing, this decreases to 3'3".

Now look at 2x8 fir joists. At 12" spacing, overhang can be 1'8". Increasing the spacing to 24" increases the allowable overhang to 2'2"!

This doesn't make sense: I'd think closer joist spacing means more load bearing capacity, allowing for longer overhangs. Even more confusing is there's no consistency between joist sizes. What gives?

5

Looks like data entry error to me. The values were reversed for several rows at some point.

Considering that they spelled 'fir' as 'fire' in one case, one can assume that accuracy was not a high priority here. That's not a flush beam, either, nor is '2x8' a 'length'.

  • +1 - but fir is how it is pronounced. – DMoore Jun 20 '16 at 22:02
  • Huh? I'm not sure what that means. – isherwood Jun 21 '16 at 13:28

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