Sistering Sagging Floor Joists....

 
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Old 03-21-2007, 03:55 PM   #1
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Sistering Sagging Floor Joists....


My boss and us are putting down wood flooring in a 70+year old house that has all sorts of humps/dips in the subfloor. Some of the joists have sagged in the middle about 1/4-1/2 of an inch(the joists are 2x8s that span 11 1/2 feet) . We jacked up the problem floor joists in the middle from the basement to flatten the floor, and sistered in new joists with nails, screws, and even 5 3/8 bolts with washers. We could not fit full length sisters up there because of space constrictions so we used two sections of 2x8s-one 8 feet long and one 2 1/2.

The first joist turned out perfect and ended up exactly where we wanted it (it did not sag when we removed the jack) but we did 2 others which had considerably more sag then the first and we probably only eliminated 50-70% of the sag and still have a dip of a little over 1/8 in the middle of these joists (on these 2 joists when we removed the jack you could see/feel the joist still coming down with it). We have to sister more but want to know what can be done to ensure the sister eliminates the sag completely. I have heard that if it has sagged alot that it might be necessary to actually cut the old joist in half or possible completely cut it through in the middle of the span-and then jack it up and sister in a joist. Anyone heard of this?

What would you guys reccomend? Thanks for the help!

Nick
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Old 03-21-2007, 04:09 PM   #2
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Re: Sistering Sagging Floor Joists....


You probably would have better luck if you leveled the entire floor before you started sistering.

The first joint was not 100% leveled. Because it was not, it pulled down the rest of the joists. An alternate messy and "by guess" method would be to raise the joist to be sisted too much so it pulls up the others to where they should be. - Too much work and over-raising could cause more problems.

The only way to eliminate the effects of out of level joists you already worked on is to raise and sister all of them and then remove the support. This way, you should get the same reults you got with the first joist by itself.

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Old 03-21-2007, 06:44 PM   #3
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Re: Sistering Sagging Floor Joists....


Yea, what he said, and, use microlams instead of dimension lumber.
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Old 03-22-2007, 08:09 AM   #4
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Re: Sistering Sagging Floor Joists....


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Originally Posted by concretemasonry View Post
You probably would have better luck if you leveled the entire floor before you started sistering.
We had actually jacked up and leveled out the 3 joists at the same time-but we did not remove all the jacks at the same time (we just removed the one under the joist after each was done)-so I'm not sure that is the problem.

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Old 03-22-2007, 04:03 PM   #5
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Re: Sistering Sagging Floor Joists....


could you have used a long (8+' as indicated) joist on either side of the sagging joist-thereby having three joists bolts together near the middle?
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Old 03-27-2007, 04:46 PM   #6
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Re: Sistering Sagging Floor Joists....


Try using LVLs or a mocro lam the same size they wont sag
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Old 03-29-2007, 10:12 PM   #7
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Re: Sistering Sagging Floor Joists....


If sister's dont hold, make a beam to carry the span and post it with loly's if you have room, that way if it ever does move again, the HO can adjust it easier.
If its all over the floor, lvl's would be your best bet!!

Last edited by IBUILD; 03-29-2007 at 10:16 PM.
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Old 03-29-2007, 10:29 PM   #8
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Re: Sistering Sagging Floor Joists....


Start by going 1/4 - 3/8" past level and use epoxies between the joists. The old joists are actually fighting you as they have been in that position for so long and may be stronger than the sisters due to being old growth wood.
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Old 03-29-2007, 11:33 PM   #9
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Re: Sistering Sagging Floor Joists....


There was an episode of Holmes on Homes a while ago with a simular situation in a century home.

He pulled the subfloor up and shimmed the top of all the joists to level. Then did new subfloor. I hate to know how much that cost.

You can kinda make it out in pictures 1 and 7.

http://www.holmesonhomes.com/episode...?sid=11&eid=19
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Old 03-29-2007, 11:45 PM   #10
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Re: Sistering Sagging Floor Joists....


Cured the symptom but not the problem?????
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Old 03-29-2007, 11:49 PM   #11
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Re: Sistering Sagging Floor Joists....


I didn't say it was the right solution

There was some issue with the tennant in the basement where they couldn't go in there and do anything.

I should ask Holmes how that floor is doing now.
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Old 03-30-2007, 05:33 PM   #12
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Re: Sistering Sagging Floor Joists....


No **** sherlock!

Is holmes full of it? Seems like he makes a living by overkill and knocking other guys' work.

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Old 03-30-2007, 07:41 PM   #13
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Re: Sistering Sagging Floor Joists....


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Is holmes full of it? Seems like he makes a living by overkill and knocking other guys' work.
He's done a lot in the last few years to expose a lot of shoddy, and I mean disgusting workmanship.

It has been an interesting show to watch and see what he finds. He's made a lot of people aware that they need to ask a few basic questions of the guy they hired from the sign on the lamp post to at least make sure they have proper insurance and a license.

Not perfect with everything he does, but he has helped a lot of people.
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Old 03-30-2007, 09:21 PM   #14
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Re: Sistering Sagging Floor Joists....


I've never seen the show but it sounds as if I could host my own. It doesn't take a lot to pick apart most builders today. Everybody is hurry-up and we'll fix the problems later........except later never comes.
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Old 03-30-2007, 09:42 PM   #15
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Re: Sistering Sagging Floor Joists....


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Originally Posted by Teetorbilt View Post
I've never seen the show but it sounds as if I could host my own. It doesn't take a lot to pick apart most builders today. Everybody is hurry-up and we'll fix the problems later........except later never comes.
It's a good show. He's gone from a half hour format, to 1 hour, to the ocassional 2-parter.

Apparently it's shown on your HOME Network down there.

http://www.holmesonhomes.com/broadca...dule.php?sid=9
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Old 02-19-2011, 11:28 AM   #16
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Re: Sistering Sagging Floor Joists....


There is a way easier way to do this stuff.

1st off I am apposed to jacking up joists if I can get away with not doing it, because it's going to cause damage to the rest of the house...I don't care how slow you do it. Secondly, the wood has taken that shape over time usually fifty years or more and is not just going to magically stay jacked up after you remove the support (and putting columns in is often times just not an option, I mean who wants columns in the middle of their living room to support the Master bedroom floor above.

Sistering is one option, but again if you jack up the floor and then sister, well the sisters are doing all the work and the existing joists are just some thing to nail to. They are doing NOTHING in the way of support, is a matter of fact they're adding more downward force on the sisters, so as a poster said before, you have to use a stronger material like micro lambs or all you've really done is bandaged the problem temporarily.

We are all familiar with the way a floor joist sags along its length. This is because to a certain extent wood is plastic. ANY house's dimensioned lumber floor joists that are more than 50 years old will be sagging along their length to some degree, I've had them sag as much as 2 inches (if it's more than that you probably have joists that are just under sized), but some where between 0 and 1 1/2 is typical.

The nice thing about a floor that has done this is that it is DONE doing it. This assumes it wasn't just under built to begin with, in that case you HAVE to sister, or put in support columns with some sort of header/beam component, but I would avoid jacking. Obviously termite damage, rot, and structural failures of one kind or another are going to require jacking.

So how do you level or straighten joists that are all bellied down along their length? Answer: Furring strips. Now wait; there is a very easy way to fur a floor with out taking ten million measurements that will leave the upper surface as straight as a string and take very little time.

1. Find your high spot (if you want it to be level and not just flat) you can do this with a laser or even a good 6 foot level minimum, if you're really Old School use a water level, they are cheap, and as good as a laser provided you mark the same point of the meniscus curve.

2. Snap some level lines off the floor at the bearing ends of the joists on both sides of the room. In other words the walls that are perpendicular to the joists.

3. Get some 2x2's and screw them down along the length of the room at the walls perpendicular to the joists under the level lines you just made. Remember wood is plastic, it will conform to the shape of the floor, and 2x2's will bend quite a lot.

4) Measure down from your level line to the height of the high spot and make a mark on the 2x2 at both ends and snap a line between them, and for gods sakes pull HARD on the line or it will sag in the middle. Now you have a straight line on a board that is conforming to what ever roller coaster shape the floor is.

5) Unscrew the board from the floor and rip the line with a circular saw (if you don’t call it a Skil I'm not sure you're qualified to read this, or your left handed in which case you're just creepy ) The line will not be straight, but generally not enough out of whack that you cant follow it with out binding the blade, just be careful.

6) Glue and screw baby. The furring strips top side will be as flat as a pancake.

7) Once you've done this with the two ends of the room you now have two boards to snap between for the strips you are going to apply on top of the joists across the room.

Now this is a fix, it does NOT address structural problems of any kind, nor is it always practical, but when you can do it I can think of no better way and it's virtually idiot proof, provided you pull HARD on the string line so it DOES NOT sag. Can't stress that enough. If your apprentice doesn't complain that you're hurting his finger then you aren't pulling hard enough.

It does often times require the removal of the sheeting, which in old houses is usually crap any way (make sure you don't cut the floor out from under the walls that run parallel to the joists), but I find as often, if not more often old houses with wood floors are on firing strips although I think this is because I live in Chicago and our fire codes require electrical conduit which was often times run across the floor hence the need to raise the floors up. If this is the case then you just pull the old ones up and put new down with this technique.

Last edited by mikej; 02-19-2011 at 02:04 PM.
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Old 02-19-2011, 11:46 AM   #17
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Re: Sistering Sagging Floor Joists....


super old thread


I like to pull strings and laminate on the side of joists and hold up to the string. the original joists have sagged and settled, they like being where they are. Unless you jack up and put in a new beam you're kinda pissing in the wind.
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Old 02-19-2011, 02:11 PM   #18
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Re: Sistering Sagging Floor Joists....


Quote:
I like to pull strings and laminate on the side of joists and hold up to the string.

Ya, so does every one else.

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Old 02-19-2011, 11:10 PM   #19
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Re: Sistering Sagging Floor Joists....


If 3 years later this guys still working on this project and coming here for advice on it, he's got a lot more problems than some sagging joists.
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Old 02-20-2011, 06:31 AM   #20
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Re: Sistering Sagging Floor Joists....


Ya ya ya I know I screwed up...I didn't look at the thread date.

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