sistering joists

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some time ago i inquired about fastening some steel plate to the sides of some 100+ year old, full dimension, rough cut oak floor joists to stiffen them up. I've decided to sister them with like sized (2x8) wood instead. These are the second story floor joists and they are 2x8 and span 15.5 feet. I've got the ceiling out on the lower level and want to stiffen them up before i go back with new ceiling. My question is, what is the best way (and frequency) to attach them? Screws, nut and bolt, nail, glue, etc?? It's a balloon style house and i'll be able to set the new sisters up on the ledger board like the originals. My main concern is pulling them together in such a fashion as to best create a "oneness" .
thanks!
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Steve Barker
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On Sun, 22 Jan 2012 22:02:59 -0600, Steve Barker

If possible to have enough open time, I'd use some adhesive too. A bead of construction adhesive along the length, then nail in place. Give the wood is rough cut and old, adhesive may not do all that well though.
I've seen a few methods. Driving a pair of 16d nails every 12", alternatively, a pair of screws about the same distance, and bolts through. Good reason to buy a nail gun that will fit in the space between joists.
I'd take a look here too http://www.finehomebuilding.com/PDF/Free/021184090.pdf
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I would think the joists are 2' apart. I suppose you know to put the crown, of the sisters, up. Lift the old joists, a bit, by jacking, before attaching the sisters, if the lifting doesn't interfer with anything. X bracing between the joists would hurt, either, if convenient.
In order of my preference, with construction adhesive: 1) nut and bolt, 2) lag bolts, 3) nails... staggered top and bottom every 12"-16".
Sonny
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On 1/22/2012 10:44 PM, Sonny wrote:

Thanks for the reply. they are somewheres in the 16" range oddly enough. (my wall studs range from 12" to 20". LOL! ) Working with this old house (1871) has certainly been enlightening.....
I was wondering about the nut and bolt thing. If drilling all those holes would weaken more than helping. I do have a right angle drill and can do that.
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As long as you keep the bolts in the middle third of the joist depth, the holes won't matter. If you decide to use double rows of the SDS 1/4" screws keep them at least 2" from the top & bottom of the joist.
cheers Bob
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On 1/23/2012 12:35 AM, DD_BobK wrote:

:)
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That was supposed to be ... wouldn't hurt, ....
Sonny
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On 1/22/2012 10:34 PM, Ed Pawlowski wrote:

Thanks Ed, for the reply and the link. Open time won't be a problem. It's been open for 6 years now. another few days or weeks won't make a difference.
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A couple comments & questions......
What are the actual dimensions of the original oak joists?
If they are 1-7/8 x 7-7/8 (or are they larger?) and the dimensions of the sistering joists are 1.5" x 7.25", the sistering process will only add 62% to the floor stiffness.
The old oak will probably not be very accepting of nails. :( This is unfortunate since nailing is a great way to a create a "no slip" connection.
Bolts are a less than optimum way to sister joists....too much slop in the holes.
To get the sister joists to accept some of the dead load & to preload load them, I would suggest jacking up each old joist slightly and holding that position while attaching the sisters.
My preferred method of sistering the joists is to use Simpson 1/4" x 3" SDS Drive Screws http://www.strongtie.com/products/connectors/SDS.asp A single row of screws at 12" o/c should be adequate since each screw is good for ~200lbs+. Double rows staggered at 12" o/c would be great but over kill.
I suggest match drilling both joists at 3/16", see how that works for oak joists to avoid splitting. These screws should pull the joists together nicely.
cheers Bob
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On 1/23/2012 12:15 AM, DD_BobK wrote:

They are about 1 3/4 x 7 5/8 i'm a thinking. (i'm not where they are right now.

I had already planned to do this. I think they will jack up a half inch or better without too much effort.

I think this is the product that was suggested when i was contemplating putting on steel plate.

Do they need washers, and
Would you still apply construction adhesive with this fastener program?

Thanks for the help, Bob. I think the fastener idea is great and will plan to use them.
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Steve Barker wrote:

Yes. As much adhesive as you can possibly apply. a) Adhesive and its application is cheap, b) It can't hurt, and c) A massive layer of adhesive can spread the shear force over a huge area.
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Construction adhesive and nails work for me, as long as the joists are straight and come together. Simple and I'd say about as effective as anything else for the application. The point to joining them together is to prevent them from bowing laterally and you don't have major force in that direction.
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On 1/23/2012 7:44 AM, snipped-for-privacy@optonline.net wrote:

Thanks for the reply!
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wrote:

t4-
Nails are very good for shear transfer (no slop in holes like bolts) but that 100 year old oak may not accept them readily.
Depending on the sister joist geometry, the SDS screws may or may not need to take much shear load. It all depends on the load path. If the sister joists bear up against the floor sheathing and the sister joists bear against the ledger (with or without blocks), then the screws will carry very little shear.
If the sister joists only bear on the ledger & not against the floor sheathing, the SDS screws will wind up taking load out of the original joist and into the sister joist.
Getting the sister joist to bear cleanly & continuously against the floor sheathing will be difficult. The SDS screws (or adhesive) will do the important job of getting the old & new joist to work as two springs in parallel.
Lateral support of the new joist is a secondary task for the screws, composite action is the primary.
cheers Bob
cheers Bob
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On 1/23/2012 5:43 AM, HeyBub wrote:

thanks!
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when this old house sisters beams they always use a single bead in a continious lazy S fashion.
using a massive amount of adhesive may not help.
they showed a previosly sistered beam that someone used circle adhesive.
it didnt adhere, the circles trapped air and prevented adhesion.
in any case use carriage bolts to hold it alltogether..... if its a bad issue add a steel plate between the sisters for extra stability
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Bolts require a hole tat least as large as the bolt shank, this makes a sloppy fit. Lags (SDS) screws need a pilot hole (screw root diameter or smaller), makes for excellent shear transfer..... no slop.
cheers Bob
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Adhesive is great, lots of contact area to spread the load. But adhesive can be really messy and two rows of SDS screws is plenty of shear transfer.
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wrote:

A good nail gun should be able to handle it, but it would need to be tested. I have seen shipping pallets made of some incredibly hard lumber and nailed together. The nails will break rather than pull out.
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EXT wrote:

Given your average sweet-gum tree, about all you CAN make of it are pallets and shoring material for deep trenches.
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