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Holes in floor joists are close to the edge


jayclen's Avatar
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04-03-11, 03:07 PM   #1  
Holes in floor joists are close to the edge

In my basement there are 2x8 floor joists that are 16" on center, and they're 14' long. The length of the joists between the main support beam and the basement wall top plate is 13' if I exclude the overhang at each end. I don't know which length to focus on, but I'm figuring the 13'. There are 1 1/4" holes drilled through all of the joists for the entire length of the basement for running cat5e & coaxil cables. I have read that bored holes should be in the middle 1/3 of the height of the joist (height is around 7 1/4"), and that holes should be at least 2" from the top and bottom edges. The holes are 1 1/4" from the bottom edge, and is 4' 3" from the end of the joist that is on the basement wall top plate. Should I be concerened with this since it does not meet the 2" requirement? The rooms above consist of two bedrooms & a living room.

Any feedback will be appreciated. Thank you!


Last edited by jayclen; 04-03-11 at 05:33 PM.
 
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jayclen's Avatar
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04-03-11, 05:44 PM   #2  
I'm thinking that the hole location is ok because the hole is located between the end and the middle 1/3 of the span. The chart at the link below shows that for a 2x8 joist a maximum notch size of 1 3/16" deep is permitted in that section, which is just shy of 1 1/4" (the hole size). The notch would be on the edge, but since the hole is higher up there is more strength there. If anyone has some thoughts to share please do. Thanks.

Maximum Bore & Notch Size Chart

 
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04-04-11, 03:08 AM   #3  
I should think you would be OK with it being on the end of the joist, more or less. My only question would be why did they bore a 1 1/4" hole for cat 5? Seems like overkill.

 
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04-04-11, 03:56 AM   #4  
Thanks for the response. A larger hole was put there to accomodate several cat5e & coaxil (RG6 quad shield) lines per room, and to avoid creating another set of holes if necessary. If the hole location wasn't safe would sistering the joists be the solution to strengthen it? I think I'm fine the way it is, but I am curious about what would be done in that case.

 
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04-04-11, 03:58 AM   #5  
If the holes were in a critical point, removing the wiring, sistering the joists and redrilling holes in a more compatible place would have been the trick.

 
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04-04-11, 10:34 AM   #6  
That's good to know. Would sistering the joist involve attaching 2x8 boards to each side of the joist? What would the length be of the boards used?

 
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04-05-11, 03:04 AM   #7  
8' long going 4' each side of the holes will be sufficient. Glue and screw to the existing joists. Adding one is enough but 2 will only add even more support. Remember that 2x8 joists 16 on center were minimum code for a single floor house. Another option could be to use 3/4 plywood on both sides instead of a 2x8 and sandwich the exisitng joist that way but also going out 4' each way of the hole. Again glue and screw.

 
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04-05-11, 10:23 AM   #8  
Do you know whether or not sandwiching the joist with 2x4 is acceptable or would I have to use one of the other options that have been mentioned? If I ever decide to reinforce the joists at some point using 2x4 would be easiest and allow me to keep the wires and hole where it currently is.

 
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04-05-11, 03:03 PM   #9  
A 2x4 won't add enough structural integrity that is needed. The holes themselves and their locations would be the problem, but as we stated, you probably won't have a problem with them.

 
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