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sagging floor remedy

bradmd | Posted in General Discussion on December 29, 2004 02:05am

So I agree to buy the wife a dining room set (table hutch buffet – the works).  In exchange, I’m granted an extension to my deadline for finishing the basement by 1.5 years (no nag period).  Dining room set shows up in time for us to have Christmas dinner on it.  Wife is happy – I’m happy.

Except the hutch is so heavy the floor is sagging.  Construction is 2×10 spanning 15 feet, spaced 16 in on center.  Sag is about 1/4 to 3/8.  To make matters worse, entire weight sits on one joist – hutch runs parallel to joist.  Behind hutch is non load bearing wall in which the Kitchen cabinets hang.  Stove and refrig. against this wall.  This wall sits in middle of two joist and is nailed only to the decking.  One of the joist is holding up the hutch.  Kitchen floor sagged a little, now more so with hutch.

I was not looking for a new project, but now I must strengthen the floor.  In reading the archives, it seams their are two ways to go:

1) some how thread additional 2×10’s in to place and sister with existing joist with nails (after floor has been unloaded and perhaps lifted a bit with a jack).  Seams that glue is not required in the act of sistering.  I can lay the 2×10 side ways and insert from the opposite side of the steel beam (beam runs down middle of house – joist span 15 feet either side).  Do to obstructions, not all new joists can be sistered to existing joist – would require a 2x spacer.  Would this be a problem?  Some of the existing joist have a cup/bow (top to bottom) and by sistering with a new joist it looks like I would have to bolt the two together to draw them tight.  See any problems here?  When I insert the joist sideways into the space and then turn it 90 degrees to be vertical, I’ll need a big hammer to force it into position.  Any problems here?

2) second method: use 3/16 steel sheets as long as possible to sister with joist.  Bolt through every xx inches?  This would also require lifting the joist a bit with a jack along with unloading the floor.  It would be easy then method 1) since its easy to avoid obstructions.  The cost will be higher with the price of steel what it is.  What about the joist that are cupped/bowed?  At 3/16 thick, I’m not sure the steel plate when drawn together will eliminate the cupping.  Over a 15 foot span what length plate should one plan for?

I’ve considered adding block in between the joist, but given the weight I’m dealing with, sistering additional joists or steel plate seams better.  BTW the hutch weights 600 pounds empty over a footprint of 7.5 sq ft.  Live load is then 80 lbs/sq ft.  And yes the floor bounces (with it the china hutch sways).  FYI, the house is 9 years old and I’ll do the work my self (engineer).

Thanks for your input

 

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  1. MikeSmith | Dec 29, 2004 02:11am | #1

    when you go to roll the sister... you don't need as big a hammer if you skin the edges where it will rub..you can always shim the ends if you need the new joist to have full bearing

    the strength comes from the sistering & bolting together... so they  act as one built-up joist  

    2x10's at that span are maxed out.. you may want to triple that particular joist

    and as for the steel.. what you are describing is a "flitch plate"  it is only effective if it is full length

    typically a 2x10 flitch plate will be 9" x 1/4" thick .. sandwiched between two joists and bolted  16" oc up & down... you need the sandwich to give it lateral stability and keep the plate plumb.. if the assembly can roll, it will bend easily

    Mike Smith Rhode Island : Design / Build / Repair / Restore



    Edited 12/28/2004 6:16 pm ET by Mike Smith

    1. bradmd | Dec 29, 2004 02:24am | #3

      Thanks, Mike.

       

      What about the situation where I have to place a 2x spacer in between the existing joist and the sister?

      This is due to the overlab joist from the other half the house that meet at steel beam. 

      1. MikeSmith | Dec 29, 2004 02:31am | #4

        use a solid spacer... that will be the 3d joist..

         again.. it  is not (neccesaralliy ) a bearing problem.. it's a defletion problem.. the overlap amounts to what  ... 12" ?.... that 's close enough to the end so yu are still getting benefit from the shortened joist

        the WORST thing that can happen from this pragamatic engineering approach is that  the triple joist won't completely solve the problem... you can always post down from this new triple joist  unless that is completely objectionable

         Mike Smith Rhode Island : Design / Build / Repair / Restore

  2. JohnSprung | Dec 29, 2004 02:21am | #2

    Also, when you roll the sister, start with the top against the existing joist and subfloor, and clamp/hammer the bottom over.  That way you're rubbing the bottom edge of the sister against the plates/steel beam.  That's a lot less area for friction to act on than if you put the bottom in first and tried to force the top in friction against the bottom of the subfloor. It's also easier to swing against the bottom than the top.

     

    -- J.S.

     

  3. DanH | Dec 29, 2004 02:53am | #5

    You might want to reconsider simply installing blocking. Done properly (good and tight) it transfers the load to the adjacent joists. You should be able to achieve about a 2x improvement for a single joist.

    In any event, even if you do sister, also install blocking.

    1. JohnSprung | Dec 29, 2004 03:11am | #6

      Blocking keeps the bottom edge of the joist from moving sideways, and therefore keeps the joist from twisting.  To the extent that twisting is what's causing the deflection, blocking will solve the problem.

       

      -- J.S.

       

      1. DanH | Dec 29, 2004 03:12am | #7

        Blocking also transfers load to adjacent joists.

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