Joist – Hard to Sister
A joist was cut, and I sistered it. However, the joist now is in the path of a toilet flange (which accounts for the original cut).
To get the additional joist to fit, I laid it on the two supporting walls nearly horizontally, and then used a series of clamps to get the board vertical, then bolted the joists together.
The other side of the wall has an open width of about 6 inches, and I was unable to fit the whole, additional joist in that space.
If there is a common way to sister the joist in this case, or an alternative, I would appreciate it. I have read a few things – metal strapping, or using a partial joist that does not reach both walls – but they don’t seem as strong as a sistered joist.
I thought of ripping a new joist into two 3.75 pieces, and putting the bottom piece in first, and then fitting the second piece on top of it.
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Attached is a photo. Note, someone had already previously sistered the joist, but that joist did not reach both walls, which seemed weak, so now there are 3 boards sistered.
Erich,
I tried but failed to understand your meaning. Maybe another GBA reader understands your question, but I don't.
-- Martin Holladay
Erich, it sounds like you are struggling with rotating the new joist into place due to the tight fit. You can rip a bit off the height of the new joist without completely ruining its strength, if that helps. There are two forces to be concerned with, shear and bending. Unless there are large loads on the floor, shear--the reason you want the ends to be supported--is not a big load, and can be adequately transferred through glue and a few bolts or structural screws.
More important in most cases is stiffness in bending:
(2) 3.75" rips together: 63% as stiff as a full 2x6. It doesn't matter if they are side by side or stacked.
A 4.5" member would be 55% as stiff.
A 5" member would be 75% as stiff.
Or you can notch just the ends, but it's best to notch with a long, tapered curve shape instead of a sharp right angle, to avoid a stress crack in the new member.
What might be easier for you is to simply stop the sistered joist short of the bearing wall. With construction adhesive and several bolts or structural screws, you will adequately transfer the load to the existing joist in most cases.
Erich,
Mike has pretty comprehensively covered the options, but just to reinforce one aspect of his response:
You wrote:
"Note, someone had already previously sistered the joist, but that joist did not reach both walls, which seemed weak"
If the joist was adequate for the loads before it was notched, adding another to strengthen it that is cut short so it doesn't bear on the walls still leaves the same amount of bearing as was there before the notching. As long as the two joist are well attached, having just one resisting the shear loads on the wall is fine.
Hi Malcolm and Michael -
Thanks for your comments. It sounds like the previously sistered joist was fine as it is, without one end supported by a wall.
To sister I used lag bolts and fender washers, staggered along the top half and bottom half of the joists. Three joists on this side of the basement / kitchen had cracks. This side of the basement did not have blocking between the joists, the other half had cross bridging, and none of those joists were damaged.
The joist parallel to the bathroom wall is at about 12 inches, so a 10 inch rough in may fit. I would rather have a standard 12 inch, but 10 inch is relatively common.
Thanks again for your comments.