+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 10 of 15
  1. #1
    Join Date
    Nov 2011
    Posts
    6

    Default sagging floor joists

    i have an older one story home with basement. the floor joists are 2x8's and span 16 feet. over time they have sagged in the center. the foundation is fine, merely the age of the joists have caused them to bow downward in the center. i would like to replace my floors and want it to be level without replacing the joists,which are still fine structurally. my proposed solution is to cut 3/4 4x8 plywood into 8 long 8" high strips and attach these on both sides of each of my existing floor joists with construction adhesive and screws and staggering the plywood lengths on each side, in effect having one side comprised of 4'+8'+4' lengths and the other side of the same joist comprised of 8'+8' length.will this be structurally sound?

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,758

    Default Re: sagging floor joists

    First let me ask you these:
    1. What are the joists resting on? joist hangers or wood/steel beams?
    2. How long are the joists from one support to the other?

    You need to pin point the cause of the sag and find a good solution, better than what you described, OR send some photos, if you can.

    After that, it wil be easier to recommend a course of action.

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: sagging floor joists

    Quote Originally Posted by vejir View Post
    i have an older one story home with basement. the floor joists are 2x8's and span 16 feet. over time they have sagged in the center. the foundation is fine, merely the age of the joists have caused them to bow downward in the center. i would like to replace my floors and want it to be level without replacing the joists,which are still fine structurally. my proposed solution is to cut 3/4” 4x8 plywood into 8’ long 8" high strips and attach these on both sides of each of my existing floor joists with construction adhesive and screws and staggering the plywood lengths on each side, in effect having one side comprised of 4'+8'+4' lengths and the other side of the same joist comprised of 8'+8' length.will this be structurally sound?
    Won't be enough -- at 16 feet the span is too great even if you were to sister a full 2x8 to each joist.
    It may be best to consider having a beam installed either at the mid point or at no more than 11 feet of span. This would also allow you the jack the floor level.

    Otherwise you might get away with sistering 2x12 to each joist or using steel ( heavy and expensise ).
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,758

    Default Re: sagging floor joists

    Quote Originally Posted by canuk View Post
    Won't be enough -- at 16 feet the span is too great even if you were to sister a full 2x8 to each joist.
    It may be best to consider having a beam installed either at the mid point or at no more than 11 feet of span. This would also allow you the jack the floor level.

    Otherwise you might get away with sistering 2x12 to each joist or using steel ( heavy and expensise ).
    OH, I missed the span, it is 16' and that is too long. I'd recommend the same thing - to add a center support beam.

  5. #5
    Join Date
    Nov 2011
    Posts
    6

    Default Re: sagging floor joists

    Thanks for the responses so far. I cannot add a beam in the center bc the basement is finished. The house was built this way over 60 years ago. Thejoists rest on the exterior concrete wall (above grade) and inside steel I-beam running the length of the house so that hosts rest upon it for the front and back of the house.

    There is a correction to the length though.the span is actually 14 feet. Once again, the interior I-beam and exterior concrete wall are fine.no structural problems.

  6. #6
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: sagging floor joists

    max span for a 2x8 joist is 12' i believe, thats with blocking and strapping.
    fire up the saw and make some dust

  7. #7
    Join Date
    Nov 2011
    Posts
    6

    Default Re: sagging floor joists

    Yes.let me deconstruct my entire home.not very helpful to cite building codes that didnt exist when the house was made. Any useful tips if my suggestion will not work?

  8. #8
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: sagging floor joists

    Quote Originally Posted by vejir View Post
    Thanks for the responses so far. I cannot add a beam in the center bc the basement is finished. The house was built this way over 60 years ago. Thejoists rest on the exterior concrete wall (above grade) and inside steel I-beam running the length of the house so that hosts rest upon it for the front and back of the house.

    There is a correction to the length though.the span is actually 14 feet. Once again, the interior I-beam and exterior concrete wall are fine.no structural problems.
    We understand there is no issue from the foundation , the joists are sagged because they are over spanned -- even at 14 feet for 2x8.
    If I recall the span table guide 2X8 has a limit of 12'6" At 14 feet your looking at 2x10 joists.

    If your basement is finished how did you plan on adding the plywood to the joists ?
    Last edited by canuk; 11-23-2011 at 06:38 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #9
    Join Date
    Nov 2011
    Posts
    6

    Default Re: sagging floor joists

    When I put in a new floor, that's when I will add the plywood on each side of the joists. Any useful suggestions?

  10. #10
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: sagging floor joists

    So , are you saying you will be tearing up the subfloor to expose the joists ?

    Btw -- we are trying to offer useful and proper suggestions
    "" an ounce of perception -- a pound of obscure "
    - Rush

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •