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How do I sister a joist?

Posted by amateurplumber (My Page) on
Mon, Aug 4, 14 at 12:39

As you can see (https://imgur.com/a/CHJPE), some dummies took a notch out of the center joist in my shower, and it was also damaged by water. I would like to sister it. I can't sister the entire length. The most I can access is that 3-4 foot section you see. As I understand it, I just glue the two together, then drill a hole and bolt some bolts in. Questions:

1)How many bolts should I use?
2)What size bolts should I use?
3)What type of bolt should I use?
4)What tools do i need to do this?
5)Do you guys have any other tips or anything?

Thanks a ton!


Follow-Up Postings:

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RE: How do I sister a joist?

I wouldn't bolt it and why can't you install a full length 2x4, after all, you have plywood on both ends, as well as sils.

Just install the full length that extends past the sils and anchor as the rest of the backing and then either screw or nail to the affected member.


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RE: How do I sister a joist?

I meant I can't tear up my house to get in a full length 2x10 haha


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RE: How do I sister a joist?

Ok, then just use a 2x4, or 6, because your goal is to strengthen the joist.


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RE: How do I sister a joist?

amateurplumber:

You want to use the same depth of lumber as the existing and make it as long as you possibly can. I'd pump a tube of constructive adhesive on the sister and drive 3" spikes in a row of 3 every foot or so.


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RE: How do I sister a joist?

"You want to use the same depth of lumber as the existing and make it as long as you possibly can. I'd pump a tube of constructive adhesive on the sister and drive 3" spikes in a row of 3 every foot or so"

To add, if you can not swing a hammer between joists, replace nails with 1/4" or 3/8" nut/bolt/washers thru drilled holes.

YMMV


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RE: How do I sister a joist?

4)What tools do i need to do this?
5)Do you guys have any other tips or anything?

When you need to ask what tools it takes to drive 3" screw into a piece of wood..

Your in over your head..

Hire someone to glue and screw a piece of 2x to the side of another.. That is not a serious load bearing joist. A piece of 2"x4"x48" and 8 or 10 3" square drive galvanized screws would work with no problems.


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RE: How do I sister a joist?

hippy,

The OP asked those questions before the answers were provided as to what needed to be done.

Or were you just kidding?


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RE: How do I sister a joist?

"...That is not a serious load bearing joist. A piece of 2"x4"x48" and 8 or 10 3" square drive galvanized screws would work with no problems."

Allow me to respectfully disagree. If this framing member fails, it could mean tile failure as well. It is important. A 2"x4" is completely inadequate to provide any meaningful additional strength which is why I recommended sistering with matching lumber. Structural screws would be fine, cheap drywall type with little strength in shear would not.


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RE: How do I sister a joist?

To "sister" a joist means adding a joist from support to support or far enough for the new joist to develop its full bending strength.

To reinforce a damaged joist over a short distance should not be done with a short length of joist but something with greater shear strength and thinner placed on each side like plywood or steel plates. It helps if the steel wraps under the joist. If the damage is in one place Metwood makes a prefabricated repair plate.

Here is a link that might be useful: Metwood repair plates


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RE: How do I sister a joist?

Hippy--I would think that our OP knows how to drive a 3" nail into a piece of wood.

I understood that he/she is asking: "which of the many fasteners that are available to me are appropriate to this job?"

I can sure as heck hammer and nail, and I've installed tons of screws, etc.

But for sistering a joist, I would wonder: Are nails enough? Is construction adhesive overkill, or is it actually bad in some way? It's not enough on its own, surely. Can I drill holes through these two joists in order to use a bolt w/ big washers on each, or does that weaken them? If I'm going to drill those sorts of bolts through, do I need to tighten them to any special tolerance, or is it enough to do what just seems sensible?

in fact, the actual information that -other- people have given the OP seems really, really helpful. In fact, it's detailed enough that it seems clear to me that this was a very intelligent question to ask, even if a person knew all about how to hammer a 3" nail into a piece of wood.

I have noticed a really snotty tone on this forum--very dismissive and judgmental. It's really too bad--it makes this a very un-safe place for people to get any help.


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RE: How do I sister a joist?

amateurplumber should be allowed to respond instead of others jumping in uninvited to nitpick. It's the ankle biting that makes the forum unpleasant.


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RE: How do I sister a joist?

Again.. That is not a serious load bearing joist.. It is under a shower stall.

The cut out in the joist does not go but about 1/2 through and does not extend the full width of the joist. A simple 2x4,6,8 or 10" sister would all work just fine.

I am willing to bet that he did not even know that it had been notched until he tore out the shower and sub floor.

The man ask..
How do I sister a joist?
and
What tools do i need to do this?

Someone ask. "How do I cook a steak" and then "What tools do I need to eat a steak with... Silver or plastic..Spoon or fork..."

Then it is time to hire someone to do it for them..


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RE: How do I sister a joist?

I don't think that steak example is parallel at all. And given that it is *not* that hard to do, why not tell them what they need to know, so they -can- do it themselves?

Or, maybe it is parallel.
It's not -hard- to figure out how to eat a steak for the first time, but a person who had only eaten lasagna or cooked grilled-cheese sandwiches might benefit from a little extra info.

Would you seriously suggest that a person hire someone else to feed him a steak, or would you just say, "Plastic would work, but it'll be less frustrating if you use metal. And it'd be easier with a steak knife instead of a regular table knife."

Would you seriously say, "You obviously don't know enough to cook a steak; go to a restaurant"? Or would you say, "Use X flame, X minutes; you can tell it's by when it feels like this. Don't poke it with a fork to turn it, and don't use tongs; use a spatula to flip it so you don't squeeze the juices out."

People who have cooked one simple thing are sensible to ask for expert advice when they're ready to expand. But wanting (or even needing) advice before doing so doesn't mean the person isn't capable of doing it successfully.

And there are supportive ways to tell someone that you suggest they get someone w/ more expertise to help them. There was a beautiful example of that elsewhere on this forum.

But I think that the level of detail given by people here and on the other thread on this topic, and the disagreements on this thread, are proof that this was a very sensible question to ask, and it in no way indicates that our OP is unable to hammer a nail or drive a screw. Or that the OP is unable to successfully support this notched beam.
It's not that hard; but there are smaller pieces of info that will make the OP much more effective at this.

If a person is just ridiculed for ever wanting to learn how to do things like this, how will they ever expand their abilities? Isn't that the purpose of forums like this, to transfer experienced knowledge to the brains and lives of those who are inexperienced but willing to get more info?


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RE: How do I sister a joist?

hippy:

You've got my curiosity up. What constitutes a "serious" load bearing joist?


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RE: How do I sister a joist?

What constitutes a "serious" load bearing joist?

The ones under the custom built 4' x 4' "closet" that holds the 600 pound gun safe before the guns are added.

The ones under the 10'x12' room that holds four 1890's -1920's Hamilton Piano's.

I would say those joist are serious load bearing when compared the load placed on ones under a shower stall per square foot.


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RE: How do I sister a joist?

Hippy:

So coming here to ask advice on how to do a home repair project is, a priori, proof that the OP is not and never will be competent to do it and should just hire a pro? Give me a break.

By that logic, NO ONE should ever attempt anything they don't already know how to do, and this forum should be closed down.

I think your posts are good evidence YOU don't have a clue how to help people who post questions here, and you should give up trying.


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RE: How do I sister a joist?

I will as soon as you tell me why it is OK to use 2x8 joist for a 12x16 deck or porch and not for a 12x16 kitchen or living room.

Would load bearing have anything to do with it?


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