[karma_carpentry]

Hi Mighty Anvil. You're right, it would not be in the way of the corridor, but it would still be in the way of the intended floor plan, and also the center of the sagging beam (its lowest point) is right there at the corner of thchimney. Maybe I could come 3-4 inches out in front of the chimney and put in a traditional lally column. How does this look in terms of getting adequate footing?

 

[mighty anvil]

To me a foot would be the minimum and 18" even better. The beam span can be effectively relieved an any point beyond the 1/3 span point on either side (or both). Once the span has been reduced by a third or more the exsiting beam strength should be more than adequate. If you intend to lift the sag, lifting at 2 feet off the center point one or both sides should still work. Design a good structure and then design the room around it. Restrictive conditions like this can often lead to great designs if you give it a chance.

Don't let the new footing touch the chimney or it's footing and don't undermine the existing soil under the chimney. Assume the soil under it is bearing at a 45 degree angle and don't break that plane within 6 or 8" of the chimney. The most important goal is to prevent the chimney from moving later and having to be rebuilt at high cost. Carefully protect what you have. The chimney is a booby-trap waiting for you to get sloppy.

Alternatively, if layout is important, jack up the beam (or level the floor above) and add one or two LVL's full span. Bolt the new to the old.

 

[ch0mpie]

as long as your new footing and chimney footing are at the same elevation, (do not dig deeper than the chimney footing or place the new footing at a higher elevation) you will not cause the chimney to settle. An eccentric loading can be handle by using a larger footing. Also what are you soil conditions? Like I said in my other post, you need to estimate the loading your new column will have on it.

 

[JustaFramer]

MA brought up a good point of not letting the new peir pad touch the chimney or it's footing. Would 2" foam around the chimney and footing work when poured for the new. Then dig out the foam and use a 2" expansion joint?

 

[karma_carpentry]

Thanks, Mighty Anvil, Chompie, and JustAFramer. This forum is the best. I hope I am not using it too much.

I understand the point about not disturbing the chimney's existing stability, and also that it's not necessary to relieve the beam so close to the midpoint. I did intend to separate any new footing from the chimney - probably by a foam separator like JustAFramer said. I also was going to be sure not to dig any deeper than the exisitng chimney's foot. Except it's unknown conditions down there - I think the chimney extends down with brick but that's just from probing with a hammer drill. I'm not even sure about that.

Good point about interesting designs growing from structural limitations. If it were my home, I would place a column about 12 to 18 from the chimney and make that the end of a little sidewall to a storage area with shelving. But this client tends to be pretty stuck upon his own designs.

I've already refused to build a stair balustrade for him because he had wide gaps of 10" in the thing. I told him the code dictates 4" max openings and that's with good reason for child safety, so he said he understood if I feel I can't build it - but didn't change the design to my suggestion. That's the kind of client he is. Really nice guy, but stuck on his designs.

 

[Greg Di]

Is there a way to dig a new footing right next to the chimney and set a 3.5" lally on it? I assume you are framing around the chimney and brace anyway, so maybe you could bury the column in the framing?

Just a thought. I'm glad I don't have to jack up that double... That's a lot of deflection to counteract. I can hear the snap, crackle and pop from here!


_______

That's what I get for posting without reading the whole thread. That was a waste of 5 minutes, huh?

 

[EngineeringGuru]

Karma-

Sounds like you figured it out. Eccentric loading on a foundation as you have sketched would be minor if you have sufficient depth to the new footing. You may want to consider extending your new footing under the existing chimney stack. Epoxy some steel from the chimney foundation to the new foundation. I would imagine that the 2" slab is a lip around the chimney and not the entire chimney foundation.

I always tell my clients to go upstairs and figure out the reason for the sagging. Check the upper level walls and attic for point loads inadvertenly placed on interior non-bearing walls. It is much easier to relocate a roof strut than it is to dig up under a house and place a footing.

Best of luck..

Engineering Guru