Cupped floor joists

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Old 01-28-15, 03:14 PM
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Cupped floor joists

I am planning on sistering 2x8's to my existing 2x8 floor joists to lessen deflection (bounce). The existing joists are code minimum spacing at 14' in length on 16" center. I am not running the sister joists across the entire span to supporting structure due to HVAC and electrical on the ends. I started the process of screwing and gluing the sister joists and then I ran into several existing joists that are cupped to the point that there's little contact with the new sister joist. The construction adhesive isn't going to make sufficient contact to be of any value. I am thinking of trying to get them somewhat flat enough to work by gradually (over a 2 or 3 week period) compressing them with scrap pieces of 2x8 on either side and at several places along the joist using (3) 1/4" X 5" bolts. They would be removed if and when it works. I've looked at a few sites that discuss code for drilling holes and notches in joists but I'm still not sure if where I plan to put the bolts is OK. Most show just a single hole rather than the three that I'd like drill up the joist in the same plane. The holes will be 1/4". So I guess my question is: can I drill one of the holes at about 1 1/2" up the joists and the then one in the middle and the last one about an 1 1/2" down from the top? Bear in mind that there will be a sister joist over the holes when completed.

___________________________________________ top of joist
| . |
| . |1/4" bolts {{{{{{{{{{{{cupped{{{{{{{{
| . |in scrap 2x8's
___________________________________________ bottom of joist

I hope that makes a little sense--

Al T
Spokane,WA
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Last edited by atodalen; 01-28-15 at 03:33 PM. Reason: added picture
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Old 01-28-15, 03:32 PM
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Stagger the bolt pattern in the sistered and original joists. Bump up to 5/8" carriage bolts with washer and nut and leave in place. Do one bolt high, then 12" over do one bolt low and repeat. Glue is not needed and it will be much stronger than what you have been doing. Don't worry about the cup, just get them bolted together tightly. For all the other ones, I hope that you are using 16d framing nails in addition to the construction adhesive or you are doing little good.
 
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Old 01-28-15, 03:50 PM
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Thanks for the reply czizzi. I was under the impression that a good construction adhesive, once cured, negates the need for heavy bolts and will lessen squeaks later. I really want to remove the cupping if possible. I've got more time than money. I've heard that the cupped joist can crack if it forced too much too soon also. I don't have any real carpentry experience so I'll have to rely on the voice of experience such as yours.
Thanks,
Al
 

Last edited by atodalen; 01-28-15 at 06:47 PM. Reason: spelling
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Old 01-28-15, 05:18 PM
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Squeaks have nothing to do with adhesive between two sistered joists. Squeaks are cause by non ring shank nails slipping in the holes or miss fires that are riding along the edge of the joists. Construction Adhesive is applies to the top of the joists during the initial build and then the subfloor is attached to the joists sandwiching the adhesive - that is to quiet squeaks. You are trying to stiffen the floor by sistering, it will do nothing as far a quieting your creaky floor.
 
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