repair of cut joist

I posted last summer asking about how to brace a joist that has a big cutout for plumbing. See
http://camoo.freeshell.org/bathtb.jpg for an picture of it. I slowly jacked up that joist and it's now level, ready to be braced.
After discussing it, I think the best way to brace it is to sandwich it between a length of 2x10 and a 3/16" steel plate. Both the 2x10 and the steel plate can rest on the sill plate. Both can extend about 3' past the cut on the other side.
I asked the plumber and he said the plumbing can be redone so there's only a minimal cut in the steel plate, which would be in front of the joist in the picture. There would be no cut in the 2x10, behind the joist.
So here are my questions :)
- What size bolts should I use to fasten the length of 2x10 and the steel plate to the joist?
- As someone mentioned, the boltholes in the wood should be drilled slightly smaller than the diameter of the bolt, to make a good snug fit. How much smaller?
- I put 3/4" plywood blocking between the joists. It's orange, you can see a piece in the picture. To the left of the picture, the plywood blocking would have to rest on a piece of the 3/16" steel plate. Do you think 3/16" thickness is enough to support that plywood blocking? There's 3/4" plywood subflooring above it that ends right next to the joist, same as the plywood blocking, so weight might be supported on that 3/16" thickness of the steel plate. The plywood blocking is quite snug next to the joist. I think it's probably fine.
thanks Laura
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On 11/6/2011 9:00 AM, Graven Water wrote: ...

3/8" would be fine; 5/16" certainly adequate.

If you use bolts that are only threaded on the ends, not full-length, the shank is full dimension and you'll have to drive a 3/8" in a 3/8" hole, anyway. Drill the hole the size of the bolts and fuggitaboudit.

...
What's the span of this subfloor you're expecting/needing support? What's the load above? If it's only a single 16" bay and there's nothing above, it'll _probably_ be fine. If it's in the middle of a traffic area or has other load, it ought to have a full header.
The 3/16" lip is ok now, but stuff does move over time and that's not much extra. Comes back to what the purpose of the blocking is intended to be; generally "blocking" is between joists only to prevent/minimize twist, not provide vertical support. As above, if there's a real need for load support I'd not be satisfied; if it's essentially cosmetic it won't matter.
--
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theres no harm in sistering TWO 1/2 steel plates across the area, along with the wood beam.. OP could also put a jackpost under the area if convenient
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On 11/6/2011 10:00 AM, bob haller wrote: ...

Whole point is what's the purpose, need?
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someday that home will be inspected before sale...
its far easier to over repair and avoid required consultations with a structural engineer, and all other hasslers at that time. think of it as belt and suspenders at a reasonably low cost
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wrote:

One did on a home I sold:( the home was 60 years old and the cut joist wasnt truly a problem. it had been like that since new.
But a home inspector flagged it, ranch house cut joist visible from basement. This caused endless grief and nearly killed the sale....
IN SUCH CASES YOUR FAR BETTER OFF OVER CORRECTING THE PROBLEM.
At home sale time in PA your required to disclose cut beam and how it was fixed or risk being sued by new homeowner. this brings questions like was repair approved by a structural engineer? documentation?
over correct the issue and who could care........
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On 11/6/2011 11:28 AM, dpb wrote:

To keep it from sagging again when the jack is removed! It was sagging so far that they spent months slowly jacking it up into it's proper position. Remove the jack and it will sag again, so the floor also will sag again.
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On Nov 6, 10:00am, snipped-for-privacy@grex.org (Graven Water) wrote:

Unless this is carrying some unusual new load of significance I don't see why you need the steel plate. Steel plate can be used in lieu of another joist, in which case you usually would use two plates, one on either side and bolt it all together. But since you're putting in a sister joist you don't need the plate and I'd keep it simple.

More reason to skip the plate all together.

I'd probably use small lag bolts.

I'd drill the holes in the new piece so the lag bolt fits in either by hand or with just a little tap from a hammer. You can pre- drill the new piece, then drill smaller starter holes in the existing one, provided you can get a drill in there.
I would also use construction adhesive on the joist before installing it. That together with the screws will give you all the structural integrity you need. After all, the existing joist is almost non-exstent, and it didn't fail. So this new sister will be fine.

No. But I don't know what the purpose is here either. Normally 2x4 or similar is used for blocking, to keep the joist from moving laterally, not plywood. And usually nothing rests on the blocking.
There's 3/4"

If you need support for the subfloor because it ends just short of the joist, nail or screw a 2x4 to the joist.
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On Nov 6, 10:00am, snipped-for-privacy@grex.org (Graven Water) wrote:

@Laura:
You need better pictures of the surrounding structure but usually when you are "patching" a hole in a floor joist like this you measure the steel plate or sistered piece of wood in feet, not inches...
~~ Evan
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There's no particular load on that area now, and it's not a trafficked area. It's near the wall and it's unlikely that anyone is going to load it so that weight will rest just on the 3/16" steel plate. But - I'm going to have the steel plate fabricated - I'll get them to drill 3/8" holes in it. They could attach an angle to the top of the plate to nicely support the subflooring. Just in case - I don't want some future homeowner to have a nasty surprise :)
I put the plywood blocking in, in order to stiffen the floor, hopefully to make it suitable for ceramic tile or stone. Which is also why I'm repairing the joist.
The gap between joists is about 14". I measured it earlier and decided I could make the bracing extend 27" past the cut, that's more accurate than the 3 feet I said above.
There's a drywall ceiling underneath this joist. I think it unlikely that a home inspector will even notice that there was a repair. When I bought the house, I don't think the home inspector noticed the cut joist. A home inspector might notice the steel plate if they look into the plumbing access. That's one reason I was going to use a length of 2x10 on the side that faces the plumbing access - it's a more standard repair than a steel plate. I think it would look good to a home inspector, 2x10 on one side, steel plate on the other side for good measure.
Yes, this joist has lasted for 50 years. Although my hardwood floor *is* sagging elsewhere - I don't think it's the cut joist where the floor is sagging, but the cut joist may have put stress on the rest of the structure.
It's not practical to sister the joist out to the next load-bearing wall. I need to use a steel plate on one side of the repair because a second 2x10 wouldn't leave room for the bathtub plumbing. The other side does have room for a 2x10, if I get the plumber to redo some pipes.
Yes, I was thinking of having a structural engineer over to evaluate the situation in person. People have also told me to header off that joist. That also doesn't look practical to me or like a good idea - it would put more of a burden on the next joist over - but perhaps a structural engineer would be able to show me how to make it practical.
I'll use lag bolts, thanks that's a good point.

You would use only 1/4" bolts? Someone else said 1/2" would be standard, but 3/8" probably ok, same 6" separation? Yes, I figured staggered, like the 5 on a die, repeated along the joist.
I was thinking 3/8" sounds about right - there are surely 3/8" lag bolts around. I'd need about 5" long bolts to go through joist, steel plate and the piece of 2x10, with washers and nuts.
I want to thank you people for actually being useful! I've had so much experience online of people not answering the question, but telling me to do something totally different that I've already considered, without being there to see the actual situation ...
Laura
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On Nov 9, 12:25pm, snipped-for-privacy@grex.org (Graven Water) wrote:

What about lags through the plate and into the wood instead of bolts with washers and nuts?
Wouldn't the washer and nut crush the wood and never get really tight? Unless, of course you used a big honkin' washer - like a steel plate perhaps. ;-)
Seriously, you can only tighten a washer/nut against wood so tight before it starts to sink in. With a washer on the head of a lag inserted through the holes in the steel plate I think you'd get a more secure connection.
Pre-drill, of course.
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On Nov 9, 12:25pm, snipped-for-privacy@grex.org (Graven Water) wrote:

Why do you think you need more than one 2x10? Sistering a joist is normally done using only one 2x10 and if done correctly it provides as much strength as a normal joist would. The joists you have are 16 inch on center and even with the one that is cut 80% way there has been no sagging for decades. Don't see why you insist on making things more complicated than necessary.
As I said before, I would sister it with one 2 x 10 using lag bolts and construction adhesive. End of story.
The other side does

More work for nothing.


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On 11/6/2011 10:00 AM, Graven Water wrote:

If you use all wood and glue and screw it, it will be much stiffer than a steel plate with bolts. The bolts in the holes will sag.
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On 11/6/2011 10:05 AM, Tony Miklos wrote:

Glue and screw does not meet any flitch plate designs from engineers that I have ever done. They have always required staggered bolts. YMMV.
Laura, if you can install a joist next to the existing from bearing to bearing, I would not worry about the steel plate. I assume that won't work for whatever reason, so you plan sounds good. I would consider 1/2" diameter bolts as normal, though I think 3/8 would be much easier to install and would be adequate for our needs.
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