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vejir
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?

dj1
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.

canuk
Re: sagging floor joists
vejir wrote:

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 ).

dj1
Re: sagging floor joists
canuk wrote:

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.

vejir
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.

jkirk
Re: sagging floor joists

max span for a 2x8 joist is 12' i believe, thats with blocking and strapping.

vejir
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?

canuk
Re: sagging floor joists
vejir wrote:

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 ?

vejir
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?

canuk
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

vejir
Re: sagging floor joists

Yes. I will be removing the old wood floor and the subfloor.
And thank you.

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