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Old 10-19-2009, 09:00 AM   #1
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Noob Needs Help With Notching In Floor Joists!

Hi All,

I need to cut a series of notches about 50-60mm deep & about 125-200mm wide across the top of floor joists pretty much smack bang in the middle. I need to place a conduit there n which I can run a large number of cables & have the option of changing/upgrading them in future - there will be a laminate flooring placed on top afterwards so I will not be able to change anything afterwards.

If I screw in metal brackets for extra support where I have cut the notches, will this make up for any loss in joist strength? What else are my options - I really need to run the cables at the top middle of the joists if at all possible - please refer to the pics below & advise if my idea is feasible?

Many Thanks,

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Old 10-19-2009, 01:47 PM   #2
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Notching is never a good idea. Holes are always better. I can't help you but the people who can (structural engineers) will need to know the size of the existing joist and the span to determine if the notches are too big.

Your better off for sure to raise the floor with sleepers and put the cable tray on top of the joists.


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Old 10-19-2009, 02:58 PM   #3
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Notches And Holes
Sec. 2326.12.4. Notches and holes. Notching at the ends of rafters or ceiling joists shall not exceed one sixth the depth and shall not be located in the middle one third of the span, except that a notch not exceeding one third of the depth is permitted in the top of the rafter or ceiling joist not further from the face of the support than the depth of the member.
Holes bored in rafters or ceiling joists shall not be within 2 inches (51 mm) of the top and bottom and their diameter shall not exceed one third the depth of the member.
Nope, unless you double the joists and the combined built-up (sistered) beams are rated to carry the load for the span.

Be safe, Gary
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Old 10-19-2009, 03:43 PM   #4
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GBR's post is spot on. Since we're talking cables can you can switch to a few smaller holes spaced widely in the center (depth wise) of the outer thirds of the joists? I'm guessing you want the flexibility to pull more cable in the future but you really don't want that big notch in the center of the span.

If you must have the flexibility to pull more cables you could put conduit through the holes by glueing together short sections (unless you have access to one end where you can feed full length conduit). When you pull your cables through also pull another pull line in for future use. You could also put in an empty conduit for future use.
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