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Old 03-24-2008, 01:13 PM   #1
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Sagging 4x6 beams under the house.


I have an addition that was built on my house about 35 years ago. The house is post and beam construction with a crawlspace underneath. The addition has 4"x6" beams 48" on center with 1.125" plywood subfloor. The original structure has a subfloor that is 2"x6" T&G, and is VERY strong, with no flex.

The original structure has pier footings every 4 feet under the 4x6 beams for support. My addition is 11'6" by 23'. The 4x6 beams span the 11'6", with NO support in between!

MY question to everyone is can I jack up the now-sagging beams and put posts and pier footings underneath?

They only sag about 1/4" - 1/2", which has caused a slope in my floor. Whille under there, I want to add 2x6 joists mentioned in another thread to eliminate all of the flex in the subfloor, as I am going to do 16"x16" porcelain tile in one area of the addition.

Also, underneath the addition is the original concrete patio that was the backyard. Will I be able to set the pier footings right on top of this concrete?

All help is appreciated!

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Last edited by Wanttodoitright; 03-24-2008 at 01:17 PM.
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Old 03-24-2008, 06:56 PM   #2
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Sagging 4x6 beams under the house.


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MY question to everyone is can I jack up the now-sagging beams and put posts and pier footings underneath?
Ayuh,.... That's how it's Done....

No Problem with the concrete either,... It'll be easier crawling on.....

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Old 03-24-2008, 07:00 PM   #3
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Sagging 4x6 beams under the house.


Thanks for the reply!

Would it be better to do 2 supports - equally placed on each beam - for the 11'6" span, or is 1 support in the middle sufficient?
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Old 03-25-2008, 06:46 AM   #4
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Sagging 4x6 beams under the house.


If you jack the 4x6 level and sister a 2x8 next to it, notched over the sills on both ends and then add two more in the 48" bay, you'll have floor joists that will span the 11'6" distance on 16" centers. Then you won't need piers and you'll have a much stiffer floor. You plan to add joists anyway, so it's probably going to give you a better job in the long run.
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Old 03-25-2008, 12:05 PM   #5
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Sagging 4x6 beams under the house.


The thread I saw somewhere else mentioned running a double 2x6, perpendicular from one beam to the next, at the point of the support (pier). Then hanging 2x6s from that, 16" on center to the sills.

You suggest 2x8 running the entire span from sill to sill. In the end, I want as little deflection as possible, at least where the tile will be installed.

Where can I acurately calculate deflection, to determine the best solution for me??? The calculators I find don't take into consideration the sublfoor, only the joists.
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Old 03-25-2008, 02:17 PM   #6
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Sagging 4x6 beams under the house.


My thinking is that a 2x8 system on 16" centers is rated to span 12 feet easily with a 10psf deadload and 40psf live load and still meet the 1/360 standard for deflection. Flooring and sub-flooring is never calculated into the deflection equation because it is not continuous across the span. It is put down in pieces and is considered part of the dead load on the joists, not part of the support. You would need to calculate the loading per square foot based on the weight of what you plan to install on the joists, starting with the subfloor, cement board, tile, etc. Then compare that to a standard span table for floor joists. For example a 2x8 on 12" centers with a 10 psf dead/40psf live load will span 14'6", while a 2x8 on 16" centers with the same loading will span only 12'7". Since floor joist tables are pretty much all based on 1/360 deflection, what it boils down to is: you either (1) Adjust the "on center" spacing (2) deepen the joist, or (3) shorten the span until your square foot loadings work out.
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Old 03-25-2008, 03:48 PM   #7
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Sagging 4x6 beams under the house.


You might need stiffer than 360 deflection for 16" porcelain tile. I'm thinking supporting the existing beams as Bondo and you discussed and adding 2 intermediate joists parallel to the beams to get 16" oc as Maintenance 6 suggests (including the supported beam).

But you might need 2x10s to get stiff enough for the big tile. You might also be able to use joist hangers to eliminate the end notches and make it easier to fit the new joist into position.
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Old 03-26-2008, 02:09 AM   #8
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Sagging 4x6 beams under the house.


This whole "why don't we tile the kitchen" suggestion of my wife's is going to be the end of me, I can see it!

Now she wants to rearrange the layout of the kitchen and add more cabinetry......"while you are going to have things taken apart anyway"......that is going to turn into extending a wall, adding outlets, upgrading some electric, among other things that she hasn't thought of, yet (I talked her out of moving a door and a window, for now).

Great ideas from you guys, I will take before and after pics as I work on this.


With what little spare time I have, this will feel like quite the project!
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Old 03-26-2008, 06:34 AM   #9
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Sagging 4x6 beams under the house.


Isn't old home renovation a wonderful thing? You get to first fix all the previous owners mistakes before you can make your own.
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Old 03-26-2008, 08:24 AM   #10
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Sagging 4x6 beams under the house.


Ayuh,......
I just can't figure out Which needs More Maintance,.....

Old Houses,........
Or,...
Wives.......

Muchless an Old House,+ a Wife with Change on her mind.........
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Old 03-26-2008, 03:26 PM   #11
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Sagging 4x6 beams under the house.


I'm thinking that the easiest way to access my crawlspace for this work will be to remove a sheet of my subfloor so I don't have to lay down the whole time.

Would it be wise to only remove one sheet, or as much as I can for a wide open work are?
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Old 04-04-2008, 07:19 AM   #12
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Sagging 4x6 beams under the house.


I guess you've got to decide that. If they used construction adhesive like they should have, you won't get the subfloor up

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