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#60837 - 01/10/06 12:04 PM Drilling floor joists
Trick440 Offline
Member

Registered: 08/15/05
Posts: 248
Loc: 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.
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#60838 - 01/10/06 12:17 PM Re: Drilling floor joists
earlydean Offline
Member

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
building code requires holes bored in joists and rafters to be at least 2 inches from the edges for structural reasons
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#60839 - 01/10/06 01:10 PM Re: Drilling floor joists
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: 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.

Alan
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#60840 - 01/10/06 01:37 PM Re: Drilling floor joists
Trick440 Offline
Member

Registered: 08/15/05
Posts: 248
Loc: Waterford, MI, USA
so 2" is safe?
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#60841 - 01/10/06 02:00 PM Re: Drilling floor joists
pwood Offline
Member

Registered: 02/04/03
Posts: 64
Loc: 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!

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#60842 - 01/10/06 05:49 PM Re: Drilling floor joists
HLCbuild Offline
Member

Registered: 12/05/04
Posts: 206
Loc: 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.

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#60843 - 01/11/06 12:25 AM Re: Drilling floor joists
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
"the reason is probably structural support" Yep!

Yes, do see this thread... http://electrical-contractor.net/ubb/Forum1/HTML/006716.html
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#60844 - 01/11/06 03:19 AM Re: Drilling floor joists
Steve Miller Offline
Member

Registered: 08/30/01
Posts: 322
Loc: 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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