Sagging joists around chimney box

[lindog]

Hi, I have some sagging joists in my basement. The reason they are sagging is that they are attached to a "box" that is built around my chimney. The chimney is between the sill plate and the other side of the support for the joists. I want to put a support perpendicular to the sagging joists right next to the chimney "box." However, the space between the joists at that spot and the furnace below it is only around 2.5-2.76 inches or so. I've thought of trying to use a 2.25" X 2.25" X 42" piece of steel ($100) or buying a sheet of 3/4" plywood (cheaper) and cutting slices around 2.5" inches wide and gluing them together. I could then place the steel or the plywood "block" into the gap and push on either end with jack posts.

can anyone tell me if the plywood will work, if the steel is the best bet or if there is another way? i won't move the furnace.

[HayZee518]

install a lally column on either side of the chimney box and jack up the joist. then install X bridging on either side of the joist to the adjacent joist. this will keep the sagging joist from twisting.

[pushkins]

I'm a little confused to what your 2.25" (anything) is going to do, unless you either jack (like Hayzee mentioned) or add another beam under the sagging joist your not going to achieve anything.
What is the joist size and how far does it span ? these are far more important questions.

Chimneys don't normally tie into any structural lumber, usually the "box" around the chimney as you call it is just a means of creating a header so other floor joists have a place to tie into.

[lindog]

Thank you to both of you for taking the time to reply.

I failed to explain the situation well I'm afraid. I am attaching a pdf that is a view from the top down, as though you were looking down through my main floor into the basement. I have labeled most of the components of the drawing.

I am concerned most about joist 3, as it is the most sagging. joist 1 is level and is resting on the foundation of the house. joist 2 sags a little, joist 4 sags some. joist 5 is pretty close to level. joist 5 is resting on a 2 x 4 on end and should be supported better than it is. the joists are all 2 x 8 solid lumber boards, and one end of each joist rests on the main beam of my house, which runs right down the middle of my basement.

The chimney is positioned right next to the stairs going down to the basement from the main floor. the red squares are planned sites for support columns. the green object is whatever i will use to lay across the columns to push up on all 5 joists (mostly 3, 2, 4, maybe some 5) to bring them all up to joist 1 level. joists 2, 3, and 4 are sort of nailed into a beam (2 x 8) that runs along the chimney, perpendicular to the joists, but there is no support under it. the reason the joists are sagging is that the old gravity furnace was below it and put out a lot of heat. also, the refrigerator is located right above joists 1, 2, 3, almost to 4. the weight and heat over the years must have made the joists sag.

The problem is that my furnace (the orange box) is under this section of joists, all along the chimney. there is only about 2.75" of vertical space from the top of the furnace to the bottom of the sagging joists. so, whatever i put across the support columns to push up on the joists will only have a depth of about 2.5" or less.

i have considered using a 2.25" x 2.25" x 42" steel, square-profile rod to lay across the columns or a block made out of pieces of plywood glued together. i will then lay the block or rod across the column plates and push up on it slowly over weeks until the joists come up.

one additional complicating factor is that joist 3 is cracked on the end next to the chimney, and i think it would be a good idea to sister a new 2 x 8 onto it to make sure it is solid.

ok, is my situation more clear now?

i've been reading that you have to use columns that are adjustable over a very small range, only about 4" to be up to code. also, i'm supposed to cement in the base of the column when finished. also, i'm not sure how to secure the rod or block to the column top to be up to code.

I forgot to say that it is about 7 feet from the center support beam to the chimney. The distance between the joists 1/2 and 3, 3 and 4/5 is around 16 inches i think

aaron

[pushkins]

Okay now it's much clearer.
Joist 1 and joist 5 are level or very close to it, 2 and 4 are pretty close (as to be expected as they run against 1 and 5 (that are level ish) and 3 is the real problem child. Just how much of a sag is there ?

Joist 3 is the problem, it's cracked which allows it to drop down dragging the other joists with it

If you can lift joists 2 and 4 level with 1 and 5 then it would be much simpler to bolt them to their respective sisters (staggered pattern on 12" centers). At the same time sister in a new joist 3 (this is 100% the problem cause) and attach it to the header with a joist hanger, then bolt the original joist to the new joist.

This should solve your problem without the need to add posts. 7' x approx. 32" is not a large area especially with 5 joists.

If you cannot lift and support the joists like mentioned above then you could look at a flitch plate design for the beam to support those joists. A flitch plate is a piece of steel sandwiched between two pieces of lumber and bolted together, a flitch plate will hold much. much more weight than either of the two options your looking at. A 3/8" x 2.5" steel plate with cut down 2x lumber bolted on 12" centers would do the job very well, have the steel supplier pre drill 3/8" holes on the centers it will save you a heap of time and cost very little more, then you could support it with your lally posts.
You are correct the lally's will need to have concrete boots on them when you have finished and they should be tapconed into the concrete floor as well. As far as