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  1. #1
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    Oct 2007
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    Question Damaged Joists Need Replacement or Sistering - Which and How?

    I recently purchased and moved into a 120 yr brick farmhouse that has a dirt basement with humidity issues (I've placed a dehumidifier in there and that has seemed to help greatly).

    The floor joists have significant insect damage. During the initial home inspection, the inspector suggested that they be replaced, but can also be sistered. He added that sistering the joists could be something I could do own my own. The insect damage has left part of the floor in one of the first floor rooms uneven.

    I would very much like to use the most environmentally sound ("green") alternative as possible, including lumber treated with borate or reclaimed hardwood or whatever.

    Bottom line, however, is that I need to address this problem. My initial question is which option - replacement or sistering - is the most practical. And if its sistering and its something I can do myself, how? I'm not an engineer, but I'm not above learning quickly. (I also have friends that are slightly more inclined to having better carpentry skills than I.)

    Any suggestions or info would be much appreciated. Thanks. (See photos attached)
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  2. #2
    Join Date
    Sep 2007
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    Long Island, NY
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    Wish I had more time to take some pic of my basement and how I
    sistered(?) mine (c:1680) but I need to get to work in the morning ....but for now let me suggest this. Green AND a great way to do what you want would be to use TJI's. Engineered lumber. YOu can go long spans with the appropriate sized TJI's and the tops of them are like a 2x3 on the flat.
    I've done both. Sort of made my own TJI's by using a flat 2x3 on top
    of 2x8's which worked great for my purposes. I also used real TJI's in other sections of the basement next to a cpl termite eaten trees...I mean floor joists...lol..
    Far as sistering per se' you can also just dble up your joists. Doesn't "have to be" nailed right to the old ones. Depends on each area you're working on.

    You can also build cribs out of plywood. Sort of long boxes out of 3/4" ply. Those are good if your floors uptop are also your only floors as in no subfloors like I have in a lot of the rooms in this old house here. The wide boxes (cribs) sort of act as flattening areas to nail the floor to as well as give it more strenth. Like I said...there's a lot of solutions for all different situations on the same project.
    In your case I "think" TJI's might be helpful...if not...forget that you ever read this post...lol.
    nite***
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  3. #3
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    Sistering is definitely easier than replacing, especially when you consider that the flooring above is nailed to the old joists. Sistering is basically sliding a new joist in beside the old one. If the old joists are sagging or the ends are damaged you may have to jack the old joist up then nail the sister joist to it. Going green is great but sometimes not appropriate and in this case I would suggest you go with pressure treated lumber. It will be in contact with concrete or stone and installed in a damp basement. Because of the thickness of your old joists you may even have to place a sister on each side of the joists.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  4. #4
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    Sep 2007
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    Quote Originally Posted by JLMCDANIEL View Post
    Sistering is definitely easier than replacing, especially when you consider that the flooring above is nailed to the old joists. Sistering is basically sliding a new joist in beside the old one. If the old joists are sagging or the ends are damaged you may have to jack the old joist up then nail the sister joist to it. Going green is great but sometimes not appropriate and in this case I would suggest you go with pressure treated lumber. It will be in contact with concrete or stone and installed in a damp basement. Because of the thickness of your old joists you may even have to place a sister on each side of the joists.
    Jack
    Just a quick note Jack..."one of the reasons" I suggested he go next to the bad beams rather than sistering to them is b/c there's no reason to remove the old and like you said the nails could be a pain that are attached to the floor above.
    Without actually seeing "how" rotted the old beams are its too hard to say what the best thing to do is. If the old beams are badly rotted they're doing little more than acting as a nailer for the floor above which is why I suggested new beams...even doubled up ones if necessary.
    Pressure treated goes without saying. You're right. And alot of engineeered wood is really weather resistant as well.
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  5. #5
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    Andy, sistering is placing the new beams beside the old without removing the old .
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  6. #6
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    I know that Jack..what I meant was not "attaching" it to the old beam. I sometimes think that if an old beam is rotted the rot can spread or pass termite tunnels along so "sometimes" rather than sistering, I just add a new beam "near" the old one on its own being that the old beam isn't doing much anyway depending on how bad it is.
    I guess if its just "cracked" thats a different case than rot. Then it would truly add to its integrity/strength.
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  7. #7
    Join Date
    Oct 2007
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    Nashville, TN
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    I'm new to both the forum and taking a crack at a 70 year-old house, so I could use some more elaboration if possible. Sorry if I ramble here.

    The basement in the house I have was finished out, but I found mold and in ripping everything out found more damage than I anticipated. I've addressed all of the moisture issues, and have beaten back the mold as far as I can but am still left with rotting boards, some with substantial termite damage (lucky me). It looks like someone tried to address these issues by sistering some joints ages ago but these boards are now damaged as well due to years(decades) of neglect while the basement was finished out. Though not sagging, the finished floor does not feel secure and shakes while walking across it. I'd obviously like to address these issues before finishing the basement out again.

    The rotting floor joists only run from the center steel joist to rim joist and obviously need to be replaced due to mold issues alone. Also this problem only concerns 6 joists. What additional information should I consider before replacing these myself? I know it is a rather broad question but this was something I never considered yet now realize it is probably what needs to be done.

  8. #8
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    Default Re: Damaged Joists Need Replacement or Sistering - Which and How?

    One of the problems with complete removal is the the floor above is nailed to the joists. That's why the preferred and easiest method is sistering to the old joists. If you treat the old joists for termites, clean up as much of the mold as you can and sister on treated joists you should be O.K. Without moisture the mold should be little problem.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

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