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  1. #1
    Timothy King's Avatar
    Timothy King Guest

    Default Rotten Floor Joists

    I need some advice on how to correctly repair several bad floor joists. The house is a single story crawlspace cinderblock foundation, it appears the yard was graded poorly and has kept the sill and joists wet for years. The grading was fixed a few years ago, but the damage had been done. The floor was sagging when we moved in and has steadily grown worse, so I crawled back there only to find a TERRIBLE MESS!
    At least 15 joists are rotted, several are very rotted, 3 have broken completly in half and the sill is as good as gone. On top of that the joists are only 2x8 on 16" centers over a 15'6" span. To make matters worse there is only about 12" of space between the dirt and the bottom of the joists leaving verry little working room.
    My plan is to replace the sill and joists with new treated wood. I do not want to sister anything just replace the whole joists. I plan to use two bottle jacks supported by two 4x4s with one jack under either end of a 4x4 post running perpendicular to the floor joists to jack the floor back into position. Then I plan to cut off the old joists within a foot or so of the outside wall and tear out what remains of the sill. I thought of using some aluminum flashing as a water barrier under the new sill to keep water from leaching up through the concrete block. After fitting the new sill I plan to slide the new joists in, on their faces, next to the old joists and then turn them up on edge and nail them in place.


    My Conscerns are:
    1) I am afraid that the rotted joists will crumble as I begin to lift the floor.
    2) I don't know what is going to happen to the floor when I cut the ends off the old joists
    3) I am betting that the header joist is bad too and I am afraid that all hell will break loose if I try ripping it out
    4) I know that 2x8s are not sufficient for a 16 foot span should i notch and use 2x 10s ?
    5) I have never replaced floor joists before and do not like the idea of being smashed under a 50 yr old house

    If you have done this and can offer any advice all will be welcome thanks
    Tim

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  2. #2
    Join Date
    Feb 2009
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    Default Re: Rotten Floor Joists

    We are home inspectors here mostly, and we are asked to not give the kind of advice that can lead to people getting in trouble or hurt.

    But since you're in Kentucky ..........

    Seriously, you should take a long hard look at this. Your house is built in a wet spot. Maybe a raised concrete slab would make a better floor.

    12" is not enough room to crawl in, let alone replace joists. Digging down will cause more water problems. That much rot makes the whole floor structure suspect. Don't forget that the subfloor will no longer be nailed down if you pull out the old rotten joists. So you will need to screw down from above into the new joists. Is the old flooring worth it?

    There are contractors here that raise houses by sliding steel I-beams under them. Rising the house will give you room to build a better foundation. I'm exhausted just from thinking about it.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  3. #3
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    Default Re: Rotten Floor Joists

    Did you get an inspection ?

    IMO.... give up any idea of replacing them from the bottom. Tear the floor out and start over. As for the span, when you install the new joists install a beam at the mid-span. This will fix any sagging problems you've had.


  4. #4
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    Default Re: Rotten Floor Joists

    Good morning, Tim:

    Your thought about limiting the amount of existing joist material left in place is a good consideration. Moisture tends to linger in existing materials that may potentially impact new materials positioned adjacent to existing. Limited air flow within the crawl space is a predominate factor that contributes to excessive ambient moisture conditions and promotes wood rot on an extensive basis -- as we see in your case.

    As you put together your plan for floor system restoration, planning adequate ventilation must occur so that your well intentioned efforts provide the longevity to this subject home. Adequate clear space between the bottom of joist and the crawl space floor should be a major component in your plan. Whether accomplished by excavating from within the crawl space or during floor removal --- if this an option that you elect -- a clear space of 24-inches between the crawl space floor and the bottom extremity of any wooden element should be considered.

    Thermally controlled foundation vents will open during the warmer spring and summer months and close during the colder periods of the year, but promote good air flow with minimal homeowner intervention...they need to be checked annually. Adequate venting units strategically installed around the crawl space perimeter will promote air flow, lessen the likelihood of elevated moisture conditions and enhance the home's longevity.

    Just some thoughts... Good luck.


  5. #5
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    Default Re: Rotten Floor Joists

    What you're contemplating is like an onion --as soon as you peel away one layer, there's another one just like it. Once you start ripping up "this & that", all sorts of "additional" damage will be visible.

    Frankly, you're in over your head. You have never replaced floor joists before, and by your own description, it is literally falling apart around you. This job needs skill, knowledge, and equipment that (by your own admission) you lack. It's time to consult with a pro.

    Good luck.


  6. #6
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    Default Re: Rotten Floor Joists

    Having grown up doing this kind of work, mostly in basements though. We don't have too many crawls around here. I have to agree with Dom, you are probably in over your head.
    With only a 12" crawl doing anything besides some hammering in place or bolting isn't realistic. I would consider your primary options as:
    1- support, raise and reframe the entire platform
    2 - take out the floor and install new joists
    3 - open one side wall and slide new joists in
    #1 - you can't do, have to hire someone, very costly might not be feasible
    #2 - can work fairly well but depends on how many partition walls you have, type of finished flooring, etc. If you have carpet and plywood who cares rip it out. If hardwood, that's painful. Under this scenario, you remove one half of the floor, install a proper midspan beam end to end, install new joists and plywood. Then do the other side, then do the finish floor. This makes installing larger joists easier and also takes some of the risk out of it. There are other issues
    #3 - You stated CMU walls; an option with this is to remove one or two blocks at a time, slide a new joist in from the side (if you have room) and keep going. This usually works better when repairing only a couple/few joists. Installing a continuous sill plate is difficult. You would also need to get underneath to do some jacking to raise the bow out of the floor to allow the new straighter joist to go in. Since you want to replace all, this probably isn't the best option.
    Under the scenario you put out I would probably spec #2 to a client. Remember you CANNOT remove old joists until new ones are set. You MUST maintain support (whatever remains) for the exterior walls. I would also move away from the idea of full length joists. Midspan beam makes the whole process so much better.
    Hope that helps

    www.aic-chicago.com
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  7. #7
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    Default Re: Rotten Floor Joists

    subfloor,bottom plates and wall studs act like straws sucking up the moisture into the wall cavities. you may find this additional work to deal with. hire a contractor if you think this job is overwhelming before you even start to do the work.


  8. #8
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    Default Re: Rotten Floor Joists

    Quote Originally Posted by Timothy King View Post
    My plan is to replace the sill and joists with new treated wood...

    I thought of using some aluminum flashing as a water barrier under the new sill to keep water from leaching up through the concrete block. After fitting the new sill I plan to slide the new joists in, on their faces, next to the old joists and then turn them up on edge and nail them in place.


    ...
    Tim
    Tim,



    Nothing about your "project" reads as "planned", "designed" or "engineered". It sounds more like someone unskilled who hasn't the least bit of knowledge is looking for a DIY instruction long-distance. You need a qualified evaluation and engineered design to both support and stablize the structure while work is being performed as well as a designed solution. Please consult a local professional to evaluate the site and conditions, and design engineered or stamped plans.


  9. #9
    Join Date
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    Default Re: Rotten Floor Joists

    Quote Originally Posted by Greg Boso View Post
    Good morning, Tim:

    Your thought about limiting the amount of existing joist material left in place is a good consideration. Moisture tends to linger in existing materials that may potentially impact new materials positioned adjacent to existing. Limited air flow within the crawl space is a predominate factor that contributes to excessive ambient moisture conditions and promotes wood rot on an extensive basis -- as we see in your case.

    As you put together your plan for floor system restoration, planning adequate ventilation must occur so that your well intentioned efforts provide the longevity to this subject home. Adequate clear space between the bottom of joist and the crawl space floor should be a major component in your plan. Whether accomplished by excavating from within the crawl space or during floor removal --- if this an option that you elect -- a clear space of 24-inches between the crawl space floor and the bottom extremity of any wooden element should be considered.

    Thermally controlled foundation vents will open during the warmer spring and summer months and close during the colder periods of the year, but promote good air flow with minimal homeowner intervention...they need to be checked annually. Adequate venting units strategically installed around the crawl space perimeter will promote air flow, lessen the likelihood of elevated moisture conditions and enhance the home's longevity.

    Just some thoughts... Good luck.
    I would say the moisture problem is from evaporation from the large dirt are under the house rather than capillary action through the block. Fixing the structural issues will only be temporary if the moisture source is not eliminated.

    If you are going with a vented crawl space then the floor needs to be air sealed and insulated.

    I think the better solution is to treat the crawl space as a short basement. The dirt floor should be sealed up either with poly or concrete to stop moisture intrusion.

    The OP talks of rotten sill plates and floor joists. The house will need to be raised enough to replace the sill plate. There are likely some issues the the rim joists too. This does sound like a complex job and an is likely not for an unskilled homeowner.


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