screw jack support posts

crawl space or basement?

crawl space it's not the best practice a poured post would be better; basement, common.

Not sure how to answer that (novice here). The addition is off the 2nd and

Based on later posting, I would count on doing some foundation work. T

So the posts, they're on the interior of a crawl space, correct? If they are, and do not come into contact with the soil or moisture, I wouldn't see why it wouldn't work. It they are exposed to the "elements" I would personally use concrete piers.

Depending on how serious you are about the house, and if this is a factor you might be able to get a credit to change it. Do you have pictures to share?

We call them helical piles. They are usually used when subsurface conditions at the usually footing level are inadequate for bearing. Steel in contact with moisture will rust....eventually. I can't advise on how long, but you have to also ask how long the building above is expected to last.