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Drilling floor joists #60837
01/10/06 04:04 PM
01/10/06 04:04 PM
Trick440  Offline OP
Joined: Aug 2005
Posts: 248
Waterford, MI, USA
This is probably a building code but...

Is there a reason we cannot drill a 1" hole in a floor joist 1.25" from the bottom of it?

I ussually drill them low because its easier to drill, easier to pull wire through, and your less likely to carelessly drill through other wires or plumbing. Other wires and plumbing are ussually supported in the middle of the joist so your hole would be under them.

This would be the joists in a basement for example.

I'm getting slack for this. They are wanting it in the middle third of the joists, the reason is probably structural support.

Shake n Bake
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Re: Drilling floor joists #60838
01/10/06 04:17 PM
01/10/06 04:17 PM
earlydean  Offline
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
building code requires holes bored in joists and rafters to be at least 2 inches from the edges for structural reasons

Re: Drilling floor joists #60839
01/10/06 05:10 PM
01/10/06 05:10 PM
Alan Belson  Offline
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Check out the 'prefab floor joists' post [lower on this page], for reasons why we don't drill holes willy-nilly in the extreme fibres of any beam.


Wood work but can't!
Re: Drilling floor joists #60840
01/10/06 05:37 PM
01/10/06 05:37 PM
Trick440  Offline OP
Joined: Aug 2005
Posts: 248
Waterford, MI, USA
so 2" is safe?

Shake n Bake
Re: Drilling floor joists #60841
01/10/06 06:00 PM
01/10/06 06:00 PM
pwood  Offline
Joined: Feb 2003
Posts: 67
castella,calif usa
2"s from the top or bottom of the joist and no greater than 1/3 the depth of the joist works for me as an inspector!

Re: Drilling floor joists #60842
01/10/06 09:49 PM
01/10/06 09:49 PM
HLCbuild  Offline
Joined: Dec 2004
Posts: 209
Herndon,Va USA
I don't have my code book handy, but I seem to remember no more than 1/4 the depth of the joist for holes.

Re: Drilling floor joists #60843
01/11/06 04:25 AM
01/11/06 04:25 AM
e57  Offline
Joined: May 2003
Posts: 2,876
"the reason is probably structural support" Yep!

Yes, do see this thread...

Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Drilling floor joists #60844
01/11/06 07:19 AM
01/11/06 07:19 AM
Steve Miller  Offline
Joined: Aug 2001
Posts: 325
Loudoun Cty, VA
Picture what drain gutter guys call a "B" bend ... that's a bend "on the flat" ... we electricians refer to it as "the way you're not supposed to bend 2 wire NM cable". This is the same effect you get on joists with the compression and tension of the joist bending "on the flat". As the joist flexes down (from the static or dynamic forces) the fibers on top of the joist compress while the fibers on the bottom stretch (tension) but the fibers in the center have the least amount of change. That's why the engineers tell us to drill the holes in the center. In real life do the joists actually stretch enough to make a difference? Who knows; that's why they (engrs and architects) get the big bucks.


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