Sistering Joists

 
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Old 01-29-2011, 08:00 AM   #1
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Sistering Joists


Mornin', My house is built using 2 x 8 joists with an approximate span of 12 1/2 feet spaced 16" oc. This is fine but there seems to be a lot of deflection, when I walk around on the 1st floor, I can hear things rattle. I was thinking about sistering maybe every other joist but I won't be able to sister the entire length. My question is, Do you guys think this would do anything or be worth the effort? Thanks in advance for helping out a dumb plumber
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Old 01-29-2011, 09:32 AM   #2
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Re: Sistering Joists


What are you better at...being dumb or being a plumber?

Read what you wrote again...you already answered your own question

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Old 01-29-2011, 09:45 AM   #3
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Re: Sistering Joists


You know the old saying, aint nothin dumber than a plumber but for the record, I'm a better at being a plumber I know that adding anything to the joists in theory would stiffen them, but I wasn't sure if it would do enough to be worth it (money & especially time wise) Thanks Greg
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Old 01-29-2011, 04:54 PM   #4
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Re: Sistering Joists


sister 2x10's next to your joists, and notch the ends if you're going over a beam or plate. add bridging blocks if you dont have any.

or run a beam and posts down the middle of the span.
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Old 01-29-2011, 09:02 PM   #5
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Re: Sistering Joists


Based on the information provided I can tell you with absolute surety that yes you should sister every other joist part way. It will be well worth the effort.


GIGO
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Old 01-29-2011, 09:29 PM   #6
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Re: Sistering Joists


I agree there robert c1
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Old 01-29-2011, 10:10 PM   #7
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Re: Sistering Joists


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sister 2x10's next to your joists, and notch the ends if you're going over a beam or plate. add bridging blocks if you dont have any.

or run a beam and posts down the middle of the span.
Agreed post & beam is your best option.
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Old 01-29-2011, 10:29 PM   #8
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Re: Sistering Joists


Yup, the specs. you provided on the floor joist span is right at the limit for #2 DF 16" O.C. x 8".

You could try solid 2 x 8 blocking at 48" intervals, this would spread the weight distribution to other joists.

Or just sister on some 8s. from about 6" short of both sides, (don't have to go on top of plates), then 16d nails two of 12" O.C.

Or a girder underneath spanning across the joists.

Lots of options.

Andy.
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Old 01-30-2011, 09:13 AM   #9
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Re: Sistering Joists


Thanks everyone, yep, it is right at the limit. Everything in this house was built to minimum code. Some stuff below minimum lol.
When I remodeled the kitchen, I discovered the stack for my master bath had only siding on top of it. In order for them to fit the 3" line in a 2 x 4 wall, they had to stuff it in there & cut the sheathing away, no insulation.
Also, to support the water lines for both upstairs baths they just added some nails to the joists, driven in at a 45, kind of like a cradle, & just laid the pipe on top, m copper none the lest...
Makes me run through a bunch of emotions everytime I have to open a wall
Thanks again, time to go get wood
Jimmy
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Old 01-30-2011, 09:26 AM   #10
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Re: Sistering Joists


I would rip some 3/4" plywood and sister both sides with that.
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Old 01-30-2011, 09:45 AM   #11
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Re: Sistering Joists


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Originally Posted by WarriorWithWood View Post
I would rip some 3/4" plywood and sister both sides with that.
My thoughts as well, plywood in rips along both sides screw and glue will help with deflection alot, it will give some strength but it is mainly there for the deflection.

Because the veneers of the plywood cross they have more compression and tension strength. Just look at the engineered wood I joist.

doing this should help alot
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Old 01-30-2011, 10:29 AM   #12
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Re: Sistering Joists


The floors very possibly have some sag in them. If you first remove some of the sag with a temporary beam and posts, and THEN install the 3/4 plywood (possibly w/ construction adhesive) you'll have an even better repair.

If a person was laminating the joists this way would it make sense to stagger the laps?

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Old 01-30-2011, 12:02 PM   #13
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Re: Sistering Joists


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The floors very possibly have some sag in them. If you first remove some of the sag with a temporary beam and posts, and THEN install the 3/4 plywood (possibly w/ construction adhesive) you'll have an even better repair.

If a person was laminating the joists this way would it make sense to stagger the laps?

Willy
from opposing sides of the joist I would say absolutely, helping the joists not to "break" in those areas. always stagger, it will always help, even if minimally.
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Old 01-30-2011, 12:23 PM   #14
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Re: Sistering Joists


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Originally Posted by Bastien1337 View Post
from opposing sides of the joist I would say absolutely, helping the joists not to "break" in those areas. always stagger, it will always help, even if minimally.
I agree, but I posed it as a question since in doing so one side might be composed of 2 strips of Plywood and the opposing side would have 3.......an extra joint, but to my thinking it would lack that stress riser.

It also seemed to me that if the surface connecting to the floor was glued it may quiet the floor. The ends where plywood ends abutt may as well also be tight and glued.

My question would be what type of fastener would be best to use and what frequency?
I think I would clamp and hammer things tight, then staple to hold and then follow with something like an 8 or 10 sinker. I'm thinking that if glue was used all you would want would be to connect the ply to the joist on each side. IF you used a 16 penny through all pieces wouldn't it tend to drive the opposing sheet away from the joist?

As other people mentioned a beam across the center would work well, but in a low ceiling it could be a problem.

Willy
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Edit; before you decide what to do run a string line across your floor and measure the amount of sag you presently have.

Last edited by Willy is; 01-30-2011 at 12:29 PM. Reason: new additional thought, not worth a post
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Old 01-30-2011, 12:25 PM   #15
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Re: Sistering Joists


solid staggered crossbridging would help if none exists.
in addition, you could possibly run a 2x6 strongback perpindicular (fastened with structural screws).
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Old 01-30-2011, 12:31 PM   #16
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Re: Sistering Joists


Quote:
Originally Posted by Willy is View Post
I agree, but I posed it as a question since in doing so one side might be composed of 2 strips of Plywood and the opposing side would have 3.......an extra joint, but to my thinking it would lack that stress riser.

It also seemed to me that if the surface connecting to the floor was glued it may quiet the floor. The ends where plywood ends abutt may as well also be tight and glued.

My question would be what type of fastener would be best to use and what frequency?
I think I would clamp and hammer things tight, then staple to hold and then follow with something like an 8 or 10 sinker. I'm thinking that if glue was used all you would want would be to connect the ply to the joist on each side. IF you used a 16 penny through all pieces wouldn't it tend to drive the opposing sheet away from the joist?

As other people mentioned a beam across the center would work well, but in a low ceiling it could be a problem.

Willy
I personally would use 1 1/2" - 2" screws on 3/4" ply. It wouldnt come through the other side. Tied in with glue it would suck it flat and I would use a nailing schedule similar to regular doubling. (2x8: 4 screws ever 12-16")

I dont think the number of joints matters so much as long as you span as long as you can between them. Realistically in a 12' run, 2 8' pieces spaced dead center on opposing sides of the joist would take the bulk of the deflection out. You probably wouldnt need to hit that last 2' sections near the ends of the joist because that is not where its greatest deflection occurs anyways.
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Old 01-30-2011, 12:34 PM   #17
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Re: Sistering Joists


In terms of the joist sag, there might not be much you can, if there are tiles on the floor above or cabinets, it could throw those out of wack, you might have to just strengthen them in place.
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Old 01-30-2011, 12:40 PM   #18
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Re: Sistering Joists


Good thoughts and advice.
I've seen some good sags in floors and just thought I would bring up that the amount of sag could determine the method of repair.

Willy
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Old 01-30-2011, 08:37 PM   #19
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Re: Sistering Joists


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I would rip some 3/4" plywood and sister both sides with that.
Agreed, A vary good idea. Fast, cheap & would work vary well.
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Old 01-31-2011, 03:17 AM   #20
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Re: Sistering Joists


Quote:
Originally Posted by WarriorWithWood View Post
I would rip some 3/4" plywood and sister both sides with that.
Quote:
Originally Posted by SAW.co View Post
Agreed, A vary good idea. Fast, cheap & would work vary well.
plywood ripped at 7 1/4" is not going to provide much strength.
better off to double up the joists, even better with 2x10's if possible.

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