Screw jacks if used right will cause allot less damage and yes always
remain stable, unlike hydraulic. In jacking a house or floor you will
affect the walls above. A screw jack can be raised in minute increments
that can be monitored better . raising a structure slowly , 4 weeks or
more per inch is important unless you don't mind large cracks in All
adjoining walls and walls above. Real slow allows your house to adjust
and not crack as much.
What are you raising, because in a 12 ft span 2 jacks will work if you
are jacking in a basement and want to be able to walk around easier. A
second floor ? 3rd floor ? 4th ? 5th?
I wonder how good the engineer was if he couldnt tell you how to do
it, because thats what it is really all about.
Depending on load there are different grades of screw jacks.