"correcting" deflection in 100-yr old floors and walls 2

[SLTA]

ok, folks.

I was asked to look at options to "repair" the sag in the floors and walls of a 100-yr old house. The house itself is rock-solid structurally, but the potential buyers don't like the sag in the floors that comes from 100 years of vertically-offset bearing walls. The non-bearing and exterior walls have also settled to match the floor sag, mostly due to some not-well-thought-out original construction. Windows have been modified to close properly, and the built-in cabinets have drawer openings that work but clearly show the sag.

Just to make it more fun, the buyer doesn't want to consider plywood shims etc, because it would mean he has to remove the original hardwood flooring. He's suggested jacking the floors, but I have troubles with that for two reasons: a) it seems to create LOTS of extra problems and b) the offset in the bearing walls would mean having shores down the middle of two rooms. Moving the bearing walls to line up vertically would also mean replacing some existing joists, as the overlap would no longer be over the existing offset wall.

And also, as a thought - does jacking slowly (like over a course of a few years) actually work? But that would mean having jacks running along the middle of their living room for years.

Any help? Any good ideas?

Please remember: we're not all guys!

 

[dhengr]

SLTA:
I didn’t mean to imply that you could remove all of the deflection and settlement in the old jsts. Certainly, there will be permanent set, you might crack a little plaster, the more so if you work to quickly. The older lumber grades, larger sized 2x12's should be adequate on those spans, except for the worst offset on the first fl. I didn’t mean it would be easy. But, I’ll bet since you are already putting in a new wall in the bsmt., if it could be put under the wall above, at 12' instead of 10', you could solve a good share of the problem. Reread my first post and resolve the questions in your own mind. If you spent a day in the bsmt. with a beam under the wall above, and a few jacks, you could get a good feel for what you might be able to accomplish. The jacks in the bsmt. for a few months might not be as objectionable as those in the Liv.Rm. I suspect that the condition on the 2nd fl. is not as serious as that on the 1st fl., and in fact the 1st fl. condition is inducing (adding to, allowing) the 2nd fl. condition. You might make the clients happy by removing two thirds of the settlement, saving the hardwood floors, and then talking about the character we like in an old house.

 

[msquared48]

Another thought here...

Although you may be able to level the floor by removing the flooring and sistering on new joists, the ceiliing finish below supported by the same joists will still read the same vertical deflection.

The buyers will be opening up a real can of worms here if they try to do this. I, too, stongly recommend against this.

Mike McCann, PE, SE (WA)

 

[samdamon]

Jacking can work, but doing it slowly is key, and as others have noted you will need to stiffen the jacked floors so that they do not simply return to pre-jacked shape after removing shores. You can monitor the force in your jacks with pressure gauges (I have used hydraulic jacks with such gauges). In a 110 + year old 4 story townhouse I jacked, we removed about 2 1/2" of deflection in every floor over the course of about two months. Each increment of jacking was from 1/4 to 3/8", applied over a few minutes, about once a week. We took gauge readings before and after each increment. We subtracted out the estimated dead load of the floors we were lifting from the gauge readings, and were able to have a feel for how much the deflected floors resisted the jacking. The small increments mentioned above were found necessary to limit the forces in the jacks and floor beams. It was very interesting to find that the gauges showed that the wood floor beams initially resisted the change in shape but then would gradually relax over the following days. (We did not wait for total relaxation, so its unclear if that is achievable.)

In this case the job was a gut rehab so damages to finishes were not a concern. But we wanted to preserve the stair rise and run as evenly as possible for each floor and keep as much ceiling height as possible. If you simply shim and level the floors without jacking you may have an uneven top riser in your stairs. Every building is different. If you can find a contractor experienced in doing this kind of work get him on board and pick his brain. It will help you decide if the time and cost of jacking are worth it.