steel plate to reinforce joist

[Graven Water]

Here's a joist under my bathtub that needs to be strengthened:

Picture at

I'm planning to attach a steel plate to the front side of this joist, and a 2x10 to the back side. The plumber said he can make a single hole through a steel plate for the drain pipe, it would not be a big cutout.

What thickness should the steel plate be? It can rest on the sill plate, and extend about 15" past the cut part of the joist. Farther if it's notched to make room for a 2x4 attached to the joist.

I got a big floor jack and I'm raising the joist to horizontal very slowly. 16" out from the sill plate, it sags about 1/3" below horizontal. That's a lot of bend in a short distance, so I figured I'll take about a month to jack it up.

thanks Laura

[willshak]

Graven Water wrote the following:

1/3 of an inch? That's a hair over 5/16". Recommended jacking is 1/8" per day, so that would take 3 days to level. 1/8" + 1/8" + 1/16". As for the steel plate, 1/8" would be enough.

[dpb]

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Between 1/4-3/8" w/ such a chunk cut out shouldn't be much of an issue on raising...I'd jack it up and see what moves as it goes--certainly a few days at most for no more than that.

If it's been that way for as long as it appears and nothing else for a load has been added, if you can actually get the 2x10 across the length on the back and get it well fastened (iow have decent access), I think the steel would be immaterial.

But, if I were going to do it, I'd probably put a piece of 3/16" plate in there to be fairly stiff. With such a large gap, it needs lateral stiffness more than anything else or it will just tend to bend sideways. Another poster suggested 1/8"; that would be fine if it had a lip bent along the top or a piece of angle to add the stiffness. Otherwise, you could fill in the gap w/ blocking and bolt thru the thinner piece to restrain it in plane.

[hrhofmann]

Seems to me that I saw that same photo a few weeks ago??

[DD_BobK]

Whatever thickness you use, it needs to be the same depth as the joist. No notches only holes and only in the middle third of the joist depth.

As dpb mentions thickness only matters due to large unsupported area (gap) ....out of plane stiffness will be an issue.

For ease of drilling & cutting I might use a piece of aluminum.....

5/16" or 3/8". I would suggest using some Simpson SDS (1/4" x 1.5" self drilling lags) to secure the metal plate to the hacked up joist.

cheers Bob

[jamesgangnc]

Yep. The suggestion then was that a couple pieces of 1 1/2" or 2" angle iron at the bottom would do without breaking into the old plumbing. All it did was sag, not fall down. Op apparently decided to rip out the plumbing and do a steel plate.

[DerbyDad03]

What's with the white paint visible in both upper corners of the picture?

Seem strange that those areas would be painted.

[Graven Water]

Yes, I can put 2x10 in the back resting on the sill plate and extending about 27" past the cut and I have good access to it. The steel plate would add some more stiffness - I'm putting in a tile or stone floor so I don't want that joist bending.

Blocking seems like a good idea. The joist is a weird width, about 1 15/16", but maybe two pieces of wood together can add up to that.

I already put plywood blocking between all the joists under my bathroom, supported by 2x4's attached to the joists. So there already is added lateral stiffness.

thanks Laura

[dpb]

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Better plan than the blocking--if using the plate as well, predrill and sandwich it between the joist and the new scab and fasten securely to the scab in the missing section area to eliminate the flex.

[dpb]

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And, if you really wanted to and can get there, you could make the plate itself as long as you can slide it behind the obstruction even if not full width(*) and fasten as can. That would lengthen the span beyond the roughly 2-ft distance over which you would be bridging.

(*) Either don't use as wide a piece the full length or have whatever notch/corner cut to clear as field fit...it doesn't have to be true rectangle.

[dpb]

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The lateral stiffness I'm talking of is for this proposed plate--if it isn't thick enough to be stiff on its own or doesn't have either the aforementioned bent lip or an angle attached on the upper edge, a piece of light steel will simply bend since there's no lateral support across that fairly long missing gap.

You don't need enough load-bearing strength vertically it would appear to make a really heavy piece of plate worth while and fabrication is probably more than it's worth as well, so you need to constrain a fairly light plate in the plane of the joist for it to be of any value for the desired load bearing capability.

Hence the earlier suggestion(s) just to make clear what the recommendation is. I think if you're going to go with the plate the latter suggestion to sandwich it between the existing joist and the new scab is the better/easier way; you can then have it already fastened to the scab and dispense w/ the other blocking and simply put in place and fasten solidly when have the desired position.