Duration of Floor Jacking Process

I’m going to second what nalusurf said – the building has taken a long time to sag and the best thing to do at this point is to replace the beam in its current position, not try to jack the whole thing back up to where it used to be. The only “jacking” that has to happen is to temporarily support the joists and lift them ever so slightly off the beam that’s being replaced so that it can be removed. The new beam then goes in exactly where the old beam was. Some shifting in the rest of the structure is inevitable in order to reconnect it to the new beam and you could see some minor cracking in the plaster. I don’t think you can avoid this by doing it more gradually but it bears discussing with your GC that your intention isn’t to make everything square again (that’s basically impossible) just to make sure that the structure is stable. Just for the record – I’m not a structural engineer but I work in historic preservation and just recently went through some structural work on an 1840s building. Good luck!

zlapqtorekgljwxy

in Renovation 8 years and 8 months ago

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badefrancis | 8 years and 8 months ago

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I got such great help on my last question that I wanted to throw another dilemma out for advice 🙂

In my townhouse the main support beam is still the original 6×6 oak beam and its cracked and turned and not properly supporting the floor joists. As a result we have a lot of sag (+1 in.) and need to replace the beam. We’ve had a structural engineer and multiple contractors out for evaluations and they said they could jack the house up and put in a new beam within a few days.

That seems like a really short amount of time for floor joists that have been sagging for decades to be pushed up without leading to cracking and splintering since they have so much “memory” that needs to be reversed. Many are already damaged and will need to be sistered, but obviously we’d like to avoid causing additional damage. Also, it seems like it would cause a lot of cracking to our plaster. (We aren’t doing a full gut reno and will preserve most of the historic layout and walls/mo ldings.)

For those of you who had to jack and replace the main beam how long did your project take and what secondary damage did you get? Did any of you work with someone who did it slowly (multiple weeks?)

daveinbedstuy | 8 years and 8 months ago

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It shouldn’t take all that long. The determining factor time-wise would be if new footings need to be dug and poured. If they don’t need to be it really is just a matter of placing a few jacks and shimming properly. And, for sag of an inch or so you shouldn’t see cracking plaster in walls to any great extent.

nalusurf | 8 years and 8 months ago

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We replaced our original girder for similar reasons plus old termite damage. Dug new footings (as DiBS said this took the most time as they need to cure and set up), temporary support of load, removal of old girder and replacing with new was all completed in several days to a week or so. We did not jack up the house but placed the girder under the existing level of the beams. I am not sure what your contractor told you in regards to the sag, but as I was taught by many knowledgeable contributors on this site, jacking up the house will not straighten your joists. As you said, the joists have been sagging for many, many decades, maybe even a century. They are now bowed like a banana. Jacking them up will lift them but won’t straighten them. So, envision pushing up from the center (the jack), and understand that the whole joist will lift, both ends too, not just the center. This is where I believe most of the issues with plaster cracking arises from. I don’t believe that you can erase this “memory” through jacking them up. The only way to do that is to sister new level joists along side them. Perhaps others will chime in…

DouglasAlan | 8 years and 8 months ago

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I’m not sure of the exact extent of what you need, but I had something similar done in like a day and a half. If memory serves, mine was a 10-foot piece of beam replaced and about three new Lally columns with new footings.