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Old 09-10-2010, 11:14 PM   #1
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question about joist sistering


2x6 nominal, sistered to 2x6 rough cut, 12' span. Wanted to make sure I did this correctly.

1) Jacked up midspans and put a crown in the original joist.

2) I put a row of 3 nails, 4 inches from one bearing point, and then nailed 16" apart, until I laid nails 4 inches from the other side of the joist. Sisters rested on the same bearing points as the original joists.

3) I did not apply glue. The old joists weren't completely straight, and with the additional work I had to do to fasten the sister, the glue would've dried up.

4) I pre-drilled holes to put the 10d sinkers in. I know, sounds weird pre-drilling holes for nails, but it absolutely had to be done. Drilled about 2" in, and drove the nail (with much resistance) the rest of the way.

Before I go on any further, does this all seem right? The second sister I put on, refused to go completely tight, but it did seem the sister would still move with the old joist (for now). Still, I'm a bit worried about the gap in between (maybe 1/8 of an inch or less). Does the sister have to be completely tight to the old joist?

Nail rows (taken from the 1st sister I put on).



Gap between 2nd sister and old joist



Any comments before I continue with more joists? Sadly, the joists still have a slight sag (although a lot less noticeable), but the floor is more level in those spots, and the deflection is so much better.

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Old 09-10-2010, 11:57 PM   #2
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question about joist sistering


Sister joists perform best when securely fastened to the existing joist by using construction adhesive and screws by using this method you make a very effective connection. While the sister joist is in position mark the position for fasteners, and any areas where construction adhesive should not be applied. Now drill the sister joist for all fasteners. This will make it much easier to install the fasteners once the joist is in position and use two rows of fasteners located about 1/4 the depth of the joist from each edge. Space the fasteners 12-16" on center and apply several beads of construction adhesive for a secure connection.
The combination of screws and construction adhesive forms a secure, squeak free connection. And yes the two joists should be tight together. You can also use a bolted connection by drilling right through both joists using ½’’ diameter bolts, nuts and washers staggered every 12-16’’ on center.
The sag can be corrected by forcing the two joists into alignment with a 2x4 which is driven under the joists to force alignment prior to driving home the screws or bolts.

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Old 09-11-2010, 12:18 AM   #3
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question about joist sistering


Quote:
Originally Posted by epson View Post
Sister joists perform best when securely fastened to the existing joist by using construction adhesive and screws by using this method you make a very effective connection. While the sister joist is in position mark the position for fasteners, and any areas where construction adhesive should not be applied. Now drill the sister joist for all fasteners. This will make it much easier to install the fasteners once the joist is in position and use two rows of fasteners located about 1/4 the depth of the joist from each edge. Space the fasteners 12-16" on center and apply several beads of construction adhesive for a secure connection.
The combination of screws and construction adhesive forms a secure, squeak free connection. And yes the two joists should be tight together. You can also use a bolted connection by drilling right through both joists using ½’’ diameter bolts, nuts and washers staggered every 12-16’’ on center.
The sag can be corrected by forcing the two joists into alignment with a 2x4 which is driven under the joists to force alignment prior to driving home the screws or bolts.
I had jacked a 2x4 under the joists prior to sistering, and crowned the old joist slightly. Unfortunately, the old joist returned to a slightly sagged position (noticed a bit by a level, but it's a lot better than before), and it took the sister down with it. Bah.

I see you talk about pre-drilling the sister, but how well would your method work when it comes to having to pre-drill the original joist? That was my main issue. If I didn't have to drill, I would've applied glue down, but since I had to drill through the old joist (which was giving rock hard resistance to nails), that didn't happen. I can imagine it would've taken forever to get everything lined up as well by myself I'll looking into bolting through though. Hopefully that'll keep everything tight.
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Old 09-11-2010, 12:20 AM   #4
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question about joist sistering


I'll be doing a bunch of that soon. I have some clamps to help draw them tight, and plan to rent an impact driver for screws. Depending on circumstances, consider adding cross-bridging.
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Old 09-11-2010, 12:38 AM   #5
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question about joist sistering


You could of used a continuous 2x2 flush on either side of the joists glued to the subfloor with construction adhesive and when the joist were level and straight drill and fasten them to the joist to hold them straight. Also the bolting is the better way to go. Are you using a cordless drill to do your drilling? If that is the case no wonder you are having problems drilling into the joists. I always use a corded drill when doing that type of work which gives me continuous power.
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Old 09-11-2010, 03:36 AM   #6
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question about joist sistering


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You could of used a continuous 2x2 flush on either side of the joists glued to the subfloor with construction adhesive and when the joist were level and straight drill and fasten them to the joist to hold them straight. Also the bolting is the better way to go. Are you using a cordless drill to do your drilling? If that is the case no wonder you are having problems drilling into the joists. I always use a corded drill when doing that type of work which gives me continuous power.
Drilling wasn't the problem (I drilled fine with a cordless, although it was a pain still when hitting the oak). Nailing was. The nail would just bend and refuse to go anywhere. Only drilling a hole into the oak joists, was it able to bite somewhat. Funny thing...the day before, I did a test. Drilled a hole out, and tapped a nail in until it was snug (and I mean tap, not pound). Next day..had to use a crowbar and a lot of frustration to get the nail out. I forgot to mention that the joists are 103 year old oak. I'm not sure if your 2x2 idea would've worked...I had the old joist jacked up with a slight crown, and sistered the new one. After it was sistered, I took the 2x4 from underneath, and unfortunately, the old joist sagged a little, and it overpowered the sister. Perhaps I'm misunderstanding how your idea would work. With that said, the sag is a lot less noticeable than before, and the floor is stiffer (thank god). I'm sure bridging will help out even more, but I'll try the bolt idea when I get a chance, to try to draw the sister even closer. I'm even considering coiled steel straps for even better stiffness, but I shall see how bridging goes.

At the very least, I'll feel safe putting a queen bed on the floor now

Last edited by Tonglebeak; 09-11-2010 at 03:38 AM.
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Old 09-11-2010, 06:22 AM   #7
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question about joist sistering


You've received plenty of good advice here. All I'd add is to emphasize that 1\2" bolts with washers would allow you to get these tighter than anything else. And given the character of old oak, you're not going to get it dead tight unless you crack your sistering. It you have any squeek - drive a hardwood shim in and glue it. Hide glue is very slow to set, just make sure it's warm enough.
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Old 09-11-2010, 08:31 AM   #8
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question about joist sistering


You have received alot of good advise on your issue. I would like to add a few more ideas. First of all to lift these joists effectively, the cheap way is to invest in 3 jack posts from Home Depot and use these to lift your sagging joist. Start one in the middle of the joist and then start the others 2' apart. Keep jacking these back n forth untill you have this joist plumb. Once you have it plumb, get your sister joist in place and nail it to hold it in place temporarly. You have to use lag bolts to hold these together !!!!!Nothing else will work as effectivly as lag bolting them together. Use 5/16 or 1/2". Use washers on both ends because if you don't they will pull right thru the wood. Use 3 bolts in line(vertically) every 2' the entire length of joist. You will need to use an impact gun to get these tight.The more expensive way to go is to rent a hydrolic house jack and do the same process......................Another thought as you jack these joists up..............have you considered what is going to happen to the walls, doorways just above this area???? When you start jacking this area up, it is going to throw all the doorways out of plumb and possible start cracking the walls as all of these areas have sagged along the joists, so by bringing the joists plumb, you have created other concerns above this area..............
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Old 09-11-2010, 10:00 AM   #9
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question about joist sistering


The reason you want to get the joists tightly connected has nothing to do with strength, and everything to do with stopping squeaks when the joists flex. If they are not tight, they will not flex the same amount when you walk on them, they will rub, and they will squeak. The glue helps hold them together to minimize squeaking, again has nothing to do with strength.

Bolting the joists together is very effective, but you need to use through bolts, which in your case would be easier anyway than trying to drive ten penny sinkers through oak. If you use 1/2 inch bolts, you oversize the hole slightly (typically 1/16 inch larger), and use a threaded bolt (called a cap screw at the hardware store) with a washer on the cap end, and double nut it with a washer on the threaded end. The bolts can be easily tightened using an ordinary ratchet, the double nutting will effectively prevent the bolts from loosening.

You can still use glue between the joists, although in my experience if you bolt it is not necessary. I like to bolt every 6 inches, staggered up and down, however this is not for strength so much as stopping squeaks. You can certainly go every 12 inches to save a few dollars in materials and some time.

To minimize floor deflection, you want to get the original joist tight to the floor before you sister the new joist in, which is where the jacking comes into place, as previously discussed on this thread. I would be cautious about overjacking an old oak beam, they tend to acquire a permanent set over time, and it is very difficult to remove the set by jacking without risking cracking of the joist. Call it old home character. I use an ordinary hydraulic car jack to do my jacking, 5 ton capacity, then hold the beam in place using temporary supports, typically a pair of 2x12's on a set of doubled 2x4 legs with a 2x6 spreader at the bottom. Seems to work fine, low tech, no rental equipment required.
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Old 09-11-2010, 12:04 PM   #10
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question about joist sistering


I'm hearing all Great comments but I have a question. The floor was designed with the current floor joists’, then adding twice as many joists, is it necessary to use thru bolts? It seems to me jack, glue, clamp, and screw would be enough.

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