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  1. #1
    Join Date
    Jun 2008
    Location
    Vallejo CA (+ Lacona NY)
    Posts
    1

    Default Mortise and tenon floor system sagging!

    I have a home in upstate New York built around 1880. The main living area is about 30' x 30' square, with a full basement. The house has a 'main beam' running the length of the main living area, and supported by one post into the basement's floor. But this post has settled (I am supposing) and the beam is sagging. This has opened up gaps between the beam and the floor joists. I know I'll have to jack up the beam and use temporary concrete footings underneath the jack stands. My question is how heavy is the load on the beam? Will one 10 ton jack be enough? Will I have to put a steel I-beam up against the main beam, and then jack the steel beam up against it?

    Thanks in advance for your ideas ... I've got another post coming: turns out they also used mortise/tenon joints to hold the ceiling joists and rafters onto the wall-top beam. As far as I can tell, the exterior wall studs are not load bearing!!!

    Picures of the house at http://picasaweb.google.com/WJHalverson

    William

  2. #2
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Mortise and tenon floor system sagging!

    I know I'll have to jack up the beam and use temporary concrete footings underneath the jack stands. My question is how heavy is the load on the beam? Will one 10 ton jack be enough? Will I have to put a steel I-beam up against the main beam, and then jack the steel beam up against it?
    Personally I would never use a hydraulic jack with a post for jacking .... it's dangerous. You have a lot of force being applied and there is a lot of restriction from from trying to do the lifting. The post will tend to go out of plumb and kick out.... when it does look out ... it will cause serious injury.

    If you think of it you are trying to balance something on a very small point on the jack ... if it's not perfectly centered , balanced and plumb ..... it will kick out.

    Instead I like to use adjustable teleposts or full length screw jacks for lifting.

    Besides depending on your local building codes these teleposts can be used as permanent support columns.

    By the sounds of it you would likely need a minimum of 3 support columns under that main carry beam .... along with the appropriate sized concrete footings.


    Just a thought.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,557

    Default Re: Mortise and tenon floor system sagging!

    Another problem with hydraulic jacks is that they sometimes creep on you under load. Jack posts are fairly inexpensive and easy to use. If you use a screw or hydraulic jack it is important to build a solid level platform to set the jack on and don't use posts on top of the jack. If you get the beam jacked up and the jack kicks out besides personal injury the sudden dropping of the beam may cause it to crack. Once the beam is in place you can install proper support posts or build a support wall under the beam. I personally don't like using jack posts as a permanent solution.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

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