I have heard conflicting informatiom about drilling holes in floor
joists. I have read that notching floor joists in the middle third of
the span is difinately out, but that floor joists can be drilled
anywhere (with the exception of on the very ends of the span) provided
the hole is not too large. (I know there are guidelines for this). I
have also heard that floor joists should not be drilled in the middle
third of the span.
Of course I found this last bit of info after drilling my floor joists
with 1 inch holes a few inches toward the end of the middle third of
the span. (1 hole per joist for a wiring run, hole in the center of
the joists, joists are 7 1/4).
Is drilling joists in the center third of the span ok or does this only
apply to notches? Thanks.
The really important thing is to drill the hole as close to the *vertical*
center of the joist as possible. A 3/4" hole centered 3 1/2" up from the
bottom of a 2x8 joist does not appreciably weaken it, regardless of whether
it's in the center third of the span, or all the way to one end.
Doug Miller (alphageek at milmac dot com)
It seems to me that a beam that's limited by vertical shear or compression
near the ends would fail appreciably sooner with a centered hole near an end.
And with lots of centered holes, it seems to me that a short beam (eg a 6'
2x8) would fail sooner in horizontal shear.
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