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Old 06-21-2011, 09:53 PM   #1
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floor joist replacement

My husband and I are recovering from a major flood(under the house, not in). We are replacing all of our ductwork. We are not putting everything back the way it was. The water wouldn't have gotten into the ducts if they had been all the way up next to the floor. We are moving the unit to a high place also. Anyway, we have some good advisors helping with the ductwork planning so that's okay. However, during the time spent under the house(crawlspace is 5' in the back of the house and about 3'6" in the front) moving electric and cable lines we have found 20 floor joists that are going to have to be replaced. We had an infestation of termites in 1996, but that was taken care of. The joists that are rotten(or eaten) are not your normal 2x8's. These are actual trees that were cut flat on two sides to a 4.5" size and the bark is left on the other two sides. What recommendations do you have for replacing what is there? We are going to run some new joists(2x10 or 2x8) and pour some concrete and make new concrete block piers for some of them, but some will have to be put right next to the bad joists. Obviously 4x4s will not be enough to take up the space and we want to make sure it's plenty strong. As you can guess, it's a very, very old house.


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Old 06-22-2011, 12:32 AM   #2
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I did an older antique house just as you have described several years ago. I was always bad to over build or over do things but the way we did was we treated the logs that were infested or were dry rotting very heavily. We used treated lumber back and placed the 2Xs one on each side of the log to be replaced. We probably could have gotten by with one 2X joist but I wanted to make sure there wasn't a joint in the flooring that broke on that log so we made sure both sides were supported.

We made drop girders at both ends of the new joists and in the middle as the span was pretty good. We did pour new pier pads and build up piers. It turned out to be a good solid floor. Just another note, many of the homes built back in the early 1800s didn't have a sub floor they just had thick flooring.


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nkjmom (06-22-2011)
Old 06-22-2011, 05:50 AM   #3
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I worked mainly on antique homes and took similar approaches. In your case, I would plan on hangers and joists as replacements. What dimensions they should be require some load calculations I would not attempt via forum posts? Without seeing plans, or even with them in hand, I think you would be very wise spending a little money to bring in an architect or a structural engineer to look things over for you. You are being given a second chance here---although I am sure it may not feel like it.

If I knew I had rotting timbers that self-served a buffet lunch and dinner on a regular basis I would want them out of there. Otherwise or just since you have access? I hope you are spraying on a suspension of Boron or leaving some diatamacious earth (swimming pool filter material). The sharpness of the minerals in either will tear the exoskeletons of insects to pieces.
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Old 06-22-2011, 07:45 PM   #4
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Okay, so after hearing from you guys that have more experience, I feel better about the situation. You didn't come up with anything really scary that we hadn't thought of. We are replacing with pressure treated lumber and actually adding piers to reduce the span length so I think it will be really much better. We are removing all the rotten wood possible and will definitely check out diatamacious earth. That is the first time I have heard of it. We know that we dodged a bullet. If we hadn't decided to move the ductwork up and do all the work ourselves we may never have realized the damage...until it was too late! Thank you for the good advice!
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