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Old 09-16-2009, 11:47 PM   #1
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Sistered OK?


Hi all,

I had a contractor sister some joists in my 120 yo house basement for my living room. My original joists are about 12" high and 4" thick. The house is a twin on stone foundation and all the mechanical's, as well as many wires, are near the problem areas. Of course.

What he did was: cut floor out 8 feet wide from center of 2nd joist from each end of room and 16ft long. He raised 3 beams about 2" with Jack Posts and then sistered 9 beams with 2x8x10's. He nailed and screwed these to originals, no glue. He didn't think raising all the beams the full amount needed would be a good idea in a house this old, so he angled the 2x8's to make the floor level. One 2x8 beam is about two inches above original. The rest are about and inch or so. These sisters are not pocketed in wall and there is no ledger to rest on or way to have hangers. They stop about an inch or two from wall.

I did question him about integrity and he replied between the 2x8x10's, nails and screws, combined with two 1/2" plywood sandwiching 1/8" luan and glue the floor is as stable as this old house can be.

Should the sisters be removed and pocketed in wall or will this damage the original beams too much? I cant run a beam on lally's across the underside, they are not even in anyway, even on the good side my room. I image these may have been hand cut on site and they didn't worry about basement bottom beams, so not milled to great extent.

Is this going to work? Should I add bolts or blocking for additional strength?

I searched forums and could find question like this, so sorry if it's already been answered. Just point the way.

Jamie

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Old 09-17-2009, 09:18 AM   #2
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Jamie,
The addition of sister joists is to control the deflection (sag and bounce) of the original joists, not to take additional loads I assume. Therefore, there are no additional forces being placed on the joist at the point of bearing at each end. The sistered joists should be just as effective stopping just short of the wall as they would be resting in a hanger or in a beam pocket in the wall itself.
Did he use deck screws to screw the joists together or did he use something similar to these?:

Deck screws lack shear strength, and nails would have been a much better option. I've seen hundreds of engineered sister joist designs in the field, and none of them called for or allowed for basic screws. Most call for construction adhesive as well, but I don't feel that's a requirement in any way (more for squeak elimination than anything). The trusslock screws shown above would work great because they're designed for this sort of application.
Short of the fact he used screws, I wouldn't have concerns.

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Old 09-17-2009, 09:57 AM   #3
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Was the reason for the sistered joists due to structural concerns due to damage to the existing joists?
KC covered the nail/screw thing but if this was for a structural application they should rest on something. Also altering the framing of a structure in any way requires a permit.
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Old 09-17-2009, 11:30 AM   #4
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Wow, thanks for the quick replies.

Quote:
Was the reason for the sistered joists due to structural concerns due to damage to the existing joists?
Some dropped in the pockets. The ones that did drop have a post directly under each joist separately, not the sister, but the original. There would be no way to place a 4x4 or 6x6 across the bottoms on two posts. They are not even in any way. Is it OK to hold individual joists in place like this? One joist was raised about 2" and he placed a post and a wedged a block of wood under the joist in the wall pocket, should this be filled in with cement or will that rot the joist?

Quote:
Did he use deck screws to screw the joists together or did he use something similar to these?:
He did use deck screws and nails. Should I get the type in the image and/or bolts? Can there be too many screws in a sister?

The contractor has the money and doesn't seem to remember to return my phone calls about my concerns (surprise, huh?), beyond the first time. To his credit he did come back and added a few extra nails.

The floor does seem solid, for now....


Jamie
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Old 09-17-2009, 11:49 AM   #5
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Quote:
Some dropped in the pockets. The ones that did drop have a post directly under each joist separately, not the sister, but the original. There would be no way to place a 4x4 or 6x6 across the bottoms on two posts. They are not even in any way. Is it OK to hold individual joists in place like this? One joist was raised about 2" and he placed a post and a wedged a block of wood under the joist in the wall pocket, should this be filled in with cement or will that rot the joist?
This is not right a post placed directly on a concrete slab with no footer to pick up a load. Wood block in direct contact with concrete. Sound like structural issues to me. This should have been evaluated by a structural engineer and permits should have been pulled.
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Old 09-17-2009, 04:18 PM   #6
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"12" high and 4" thick."----- these are almost beams as they are probably #1 old growth, very strong.

"He nailed and screwed these to originals, no glue." ------- Has been covered.

"They stop about an inch or two from wall." -------- Not a problem.

"Should I add bolts or blocking for additional strength? " ---- Those that are higher should be bolted at their ends to transfer the load to the bolts close to the original's bearing. Blocking will help distribute a load uniformly, not increase the strength for more load.

"One joist was raised about 2" and he placed a post and a wedged a block of wood under the joist in the wall pocket, should this be filled in with cement or will that rot the joist?" ---- Tack a small nail to keep the wedge there, leaving the head accessible to adjust later if needed. No concrete. If the joists are sloppy in there hole with lateral (side to side) movement, you may want to shim them in place or even add blocking (if really - 1-1/2" sloppy).

"Can there be too many screws in a sister?" ----- Staggered (20d nails per code for built-up girders and beams - but you are sistering) 32"o.c. at top and bottom and staggered at ends -- leave 1-1/2" of free wood across top and bottom for compression and tension of wood. The screws Kc said are good.

Here is some reading on sistering to ease your mind: Starting page 135: http://books.google.com/books?id=0SC...raming&f=false
Page 141 similar to yours.
Be safe, Gary
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Old 09-17-2009, 06:22 PM   #7
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A picture would help to see what this looks like
Some things show up better when they can be seen
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Old 09-18-2009, 06:48 AM   #8
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Sistered OK?


Sounds like he sistered these strictly to level the floor, not to add any structural strength. That being the case, they should be fine. I would have glued them, but I doubt you will have any issues, as long as they are secured well to the original joists. 4x12 joists are pretty massive and unless they are some excessive centers or an extreme span, they should carry the load without any problem. If the floor feels solid and is not springy or spongy, I wouldn't worry about it.
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Old 09-18-2009, 07:51 AM   #9
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The issue is not with the joists themselves but rather the degrading pockets they are resting in. The information posted hints that masonry failure is occurring. This should be evaluated by by a structural engineer to determine the severity of the degrading. Bracing sinking floor joists on posts (I assume 4" x 4" at that) with out the support of proper footings is not the solution to the problem. Sistering the joists when the joists themselves is not the problem also does nothing to correct the masonry issues.

Wood should not be in direct contact with concrete unless it is treated. A wood wedge is a temporary repair at best. The foundation issue should be evaluated by one qualified to do so to determine if continued degrading will be an issue and to determine a proper course of action. Those who would recommend a few additional nails or bolts for the sistering are ignoring the bigger underlying issue which is the degrading foundation. This is not something that can be easily diagnosed on this forum pictures or no pictures.

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