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Proby 07-28-2010 10:26 AM

Notching joists
How concerned should one be if the tops of 2x8" ceiling joists have been notched about 3/8" deep to allow wiring to fit in and put flooring on top in an attic? I know it's against code and all and it shouldn't be done, but is this a realistic safety concern? If found, should it be looked into and possibly remedied by a professional?

xxPaulCPxx 07-28-2010 01:35 PM

3/8" Notching isn't that deep. While it isn't the ideal way to run wire or pipe, it is allowed providing the joist isn't already overloaded.

Gary in WA 07-28-2010 02:11 PM

No notches in the middle 1/3 of span. This is where the compression of the fibers are the greatest under load:

How long a notch?

Be safe, Gary

Proby 07-28-2010 02:16 PM

Just enough to get wires thru, maybe 5/8" wide or so.

I thought you were allowed to notch at all, I thought you were only allowed to drill thru the center 1/3 of joists or studs.

Gary in WA 07-28-2010 11:42 PM

No notches in middle 1/3 --- that's because when the board bends under load, the top 1" of the joist fibers are under compression and the bottom 1" (or so) are under tension. To notch in this critical area reduces the joist from it's rated strength to a lower rating. If a 2" deep notch---- it would then be equal to the next size lower joist and that rating for loads. Not exactly 2" as joists go: 5-1/2, 7-1/4, 9-1/4, etc. I'm not a S.E. and don't know the exact figures. You could ask our Daniel on here..... or check out the Engineering forums for the answer of that small of a notch.,M1

Be safe, Gary

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