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Old 02-26-2013, 12:23 PM   #1
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Sistering 2nd level floor joists without jacking


I have a 2 family flat with a 1st floor apartment and a 2nd floor apartment. 1950's brick and mostly plaster walls in Washington, DC. I recently had the 1st floor apartment gutted and remodeled. When the contractor did the ceiling they shimmed the bottom of the sagging joists to make the 1st floor ceiling level (or something like that, I wasn't there). I now want to level the 2nd level floor. I am ripping up the old flooring and subfloor to expose the joists from above. I plan on sistering with new straight boards of the same width (2x8 if I remember correctly). Jacking from below is not an option. I'm not redoing the ceiling below, especially since I have a tenant down there.

1) Is it ok to sister the new straight boards to the old sagging joists? The new subfloor will obviously rest on the new straight joists, and the 1st floor ceiling will continue to be connected to the old sagging joists (Span is about 12 feet).

2) Should I sister on both sides of each joist to avoid twisting?

3) I plan on chipping away at the load bearing brick wall in order to make a gap big enough to fit the new joist into. I don't want the weight of all the new joists and subfloor resting on already sagging old joists. Is that necessary? Shouldn't be a big deal, just wondering if I needed to at all.

4) How should I plan on attaching the other end of the new joists to the load bearing wall? Do I notch/shave the end of the joist or just try to jam it into the space between the top of the wall below and the bottom of the wall above? I think I should notch b/c a tight fit with the wall above is not an issue since the roof load already transfers through the old joists to the wall below.

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Old 02-26-2013, 12:36 PM   #2
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Sistering 2nd level floor joists without jacking


5) Before I go digging into the party wall to support the new joists, how thick should the party wall be? I'm thinking it has to be more than 2 courses of brick or else the current joist cut outs would go all the way through, but I could be wrong.

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Old 02-26-2013, 02:24 PM   #3
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Sistering 2nd level floor joists without jacking


As long as ur boards rest on the bearing walls on each end it would b fine. If not ur adding more wait on ur sagging beams n it probably will start cracking n show seams in sheetrock below. Also try not hammering to hard as u sister the boards. All the hammering n movement can start cracking the spackle seams below. Maybe screw them in
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Old 02-26-2013, 03:14 PM   #4
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Sistering 2nd level floor joists without jacking


There's just no way anyone could give you an ansewer to these questions for sure without being there to see it.
Changes to the building like that would require permits, inspections, and may need an engineer to sign off.
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Old 02-26-2013, 03:46 PM   #5
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Sistering 2nd level floor joists without jacking


See below. I know sometimes consulting with an engineer may not be in the budget, or it is a hassle, etc. but I just did many of the items noted below in my house on two separate floor occasions. There are many things that go into what you are doing, so be carefully and I would certainly strongly consider an engineer to assist as insurance for your project. Remember, they are pro's, we are not I answered the below questions based on my experience a few weeks ago and based on your descriptions.

Also, I agree with Joecaption - need pics!!

1) Is it ok to sister the new straight boards to the old sagging joists? The new subfloor will obviously rest on the new straight joists, and the 1st floor ceiling will continue to be connected to the old sagging joists (Span is about 12 feet). Is only the beam sagging or are any of the bearing walls sagging? You should be able to do this without too much trouble assuming that both ends of your joists are resting on load bearing walls. Sistering without resting on bearing walls would be adding dead weight and could cause your joists to fail.

2) Should I sister on both sides of each joist to avoid twisting? Blocking

3) I plan on chipping away at the load bearing brick wall in order to make a gap big enough to fit the new joist into. I don't want the weight of all the new joists and subfloor resting on already sagging old joists. Is that necessary? Shouldn't be a big deal, just wondering if I needed to at all. ??? Yikes.

4) How should I plan on attaching the other end of the new joists to the load bearing wall? Do I notch/shave the end of the joist or just try to jam it into the space between the top of the wall below and the bottom of the wall above? I think I should notch b/c a tight fit with the wall above is not an issue since the roof load already transfers through the old joists to the wall below. A slight shave to fit exactly may be required to make it fit, but avoid it if you can. Shim afterwards for any gaps.
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Old 02-26-2013, 04:05 PM   #6
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Sistering 2nd level floor joists without jacking


From a purely structural point of view, you don't have to take the new joists end-to-end. You can stop them short of the loadbearing walls by a foot or so, as long as they are well-secured to the sagging joists (eg by bolting or screwing).

This is because the bending stress in the joists tails off rapidly towards the ends. There will be shear force acting on the existing joist-ends, but in residential floors, shear on timber joists is never a problem.

You could stop them twisting by solid blocking pieces.
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Old 02-26-2013, 04:10 PM   #7
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Sistering 2nd level floor joists without jacking


Thanks for the responses.
An engineer IS in the budget as are permits - just not a contractor
I can't show you pics because I haven't ripped the floor out yet
Chipping the brick shouldn't be a big deal. In my basement the joist gap has been widened to make room for sister joists as there was termite damage in the past. How else would one support the sister joists on the brick load bearing wall?
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Old 02-26-2013, 04:16 PM   #8
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Sistering 2nd level floor joists without jacking


Agreed, that being said there are some variables that go into that assumption. (hence the engineer suggestions). Best to 1) have an engineer look at it 2) get some pics on here. If you are changing your flooring type at all you could be adding even more stress to the already stressed beams.

That is the easier route to take but be careful on what you assume wont effect the structure. You know what they say about "ass-u-me"-ing things.
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Old 02-26-2013, 04:31 PM   #9
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Sistering 2nd level floor joists without jacking


I take it from being in DC area this is a shared wall? (i.e. no way to get to the framing members on the other side of the wall for a ledger or something similar - I guess with all the plaster on this would not be an option anyway). If it is a double brick wall you could build a pocket, but reach out to your inspector to see what his requirements are. Not sure if he would be okay with the chipping away of the structural brick. If the engineer signs off it seems like the way I would go is what tony-g has suggested. Sister the joists relatively close to the ends, use whatever fasteners the engineer deems, and add blocking to prevent twisting of the joists. Good luck!
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Old 02-26-2013, 07:03 PM   #10
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Sistering 2nd level floor joists without jacking


You want the engineer after the joists are exposed. If all the joists are sagging, you want to know why the joists are failing in that way.
One thing I don't get, is the whole of first floor is 12' only? When you say the span is 12' but the first floor ceiling had sagged, do you mean in spots or the entire floor? Was a wall removed? Was the floor just badly engineered or under engineered? Can you ask the previous carpenter for his opinion?
You can have a straight floor by sistering 2x4 or 2x6 to the existing joists. You don't have to use the matching size lumber to fix the floor. Only problem is, again, why did the lumber sag and did it stop? Somebody with experienced eye should see the actual joists. Because engineers sign off on their reports, they are the most reliable. A good carpenter with a span chart can do it too, but without a sign off, you're betting.
Joists should be sitting on stud wall plates or on studs. I don't think each joist is sitting in its own pocket in a brick wall. Anyway, the new joists don't have to have their own load bearing points. Old joist ends are enough to carry its own weight and the new sister as long as bearing points are solid and well connected.
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Old 02-27-2013, 09:12 AM   #11
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Sistering 2nd level floor joists without jacking


I just finished doing this for my floor. My span is 14' and was going to use 12' to lift a little. The only thing about this or any other way is that you have to lift the old ones up slightly then attach the new ones. Otherwise you are just reinforcing and not curing the sagging. I ended up using 14' lumber the same as what was there and I had to wedge the one end onto the beam running through. I used a utility knife to slightly shave a little off the first 1-2 inches so that I could put them kinda in place then hammer them onto the beam. Before that step though, I PL premiumed the both boards, then put it in place, c-clamped every 16", then used a framing nailer to nail it together. I put 3 nails every foot. After it was all done (23 joists), I put blocking in where I could to try tie it all together. It is a much better floor and when my kids are jumping on it, I don't have stuff falling all over from shelving units!
Hope that helps a little.
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Old 02-27-2013, 12:38 PM   #12
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Sistering 2nd level floor joists without jacking


The rowhouse is only about 20' wide. So there's a 12' span and an 8' span. I believe the sagging is caused by the original beam in the basement being replaced with a steel I-beam due to termite damage. When that was done, the entire basement floor was dug up (including load bearing columns) to fix drainage and install a french drain. I believe both the 1st and 2nd floor walls sagged causing the floor to lean towards the middle load bearing wall on both sides. I will have to rip each sister joist to be wider near the middle load bearing wall and thinner toward the outer load wall to achieve level (or shim the old joists).
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Old 03-03-2013, 03:48 PM   #13
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Sistering 2nd level floor joists without jacking


You need a engineer. You must find out why the girder sagged. Was it a mistake or a faulty installation? If you already know the answer (that an engineer told you and don't assume anything on your own or from PO's hearsay), then fine and just use 2x4 or x6 to level the floor, since the joists themselves are not the problem. If you level the floor this way, however, keep in mind that the floor extends into door ways, hall ways, kitchen cabinets, bathroom door sills, radiators, etc. You more or less have to level the whole floor and put down new floor.

It may have been easier to raise the whole building from the basement.

Have you looked at the roof? Any cracks in the 2nd floor ceiling? On site inspection is a must.

You may be looking at a money pit, unless you have a couple of years and do the work yourself. First floor repair was easy. Second floor repair is universe apart. I recommend living with it.
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Old 03-03-2013, 04:59 PM   #14
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Sistering 2nd level floor joists without jacking


Joists sag for one of several reasons.

1. They were undersized to begin with, and they deflected elastically under load.

2. Even if properly sized, all wood structural elements deflect under load, and eventually the deflection becomes permanent. This is known as creep. In your case, the house is over sixty years old, plenty of time for creep to develop.

3. The joists become damaged due to insects, cut outs, water damage etc., and lose strength. This can lead to additional deflection.

If the deflection is simply due to long term creep, there is no problem sistering an almost full length joist (no need to go to the wall). If the problem is damage to the ends of the existing joists, you need a full length sister with standard embedment into the brick.

It is not necessary to jack up the old joist, as you noted the floor will rest on the new joists. However, you will need to remove the existing subfloor first and nail it back down when you have installed the new, level joists. You should anticipate that over time, the new joists will sag a bit, but this will likely take many years, and is not a structural problem.
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Old 04-21-2013, 10:37 PM   #15
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Sistering 2nd level floor joists without jacking


"Flat"??? And here I was, thinking you were from England..DC, go figure. lol

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