What makes you think it's not load bearing? Everything you say suggests that it is. If a wall is "preventing sagging" then it is most certainly carrying a load and you'll either need to re-engineer the joists or add a beam to support the floor above.

Your post is full of ambiguities. Do you have an architect or an engineer helping you? Why would that person not be telling you how this must be done?

It seems obvious that the wall was load bearing but you don't say what the spacing is. Assuming the spacing is 16" o.c. the tables in the building code will tell you that 2x8 #2 hem-fir joists can only span 12 ft. To span 18ft would require #1 2x12 joists or 2x10 D. Fir spaced at 12" o.c.

It is also possible to use I-joists or LVL's to reduce the height of the framing.

If an architect or engineer draws the design he/she will be responsible for the structure even if they do not stamp the drawings so just do what they tell you.

Thanks for your responses. That clears up my confusion as to load bearing "ness" and joists.

We do have an architect/engineer that worked on the plan. He got the plan approved with the city, showing that 2x12@16 ceiling joists will be verified during construction. However, when we asked him why this verification was needed when he has already poked a bunch of holes in the ceiling and saw the joists were 2x8@16, he then said 2x8@16 is sufficient. In addition, the plan doesn't show that there is another level above. We asked him to revise the plan and submit to the city, but he has been refusing to do so. So here I am trying to understand the structure.

I understand that he will be responsible for the structure, but I would rather prevent faulty construction from starting, rather than finding out later and have to deal with the mess.

In terms of load bearing or not, I made that assumption, since that wall is just being knocked out without additional beam or (bigger joists). But if it were a load bearing, shouldn't there be something below also supporting that wall? I don't know if the floor below has a wall that aligns with this. I will have to check later and report.

Thanks!

If it sounds to good to be true, it probably is.

The plans should contain all the floors that affect, are affected by this remodel.

DO NOT REMOVE THAT WALL until you have hired a competant engineer.

Go ahead and knock the wall down, just don't walk around upstairs.

8s can't span that far. I have no engineering or architectural degree, but 8s can't span that far. Fire this guy.

Reporting.

There is a wall in lower level (below the wall to be removed), but it is off by about 6 inches. Also it doesn't span across the entire length of the wall we are trying to remove. It is about half that long and the other half is a doorway and a hallway.

A bearing wall below can be offset up to a foot from a bearing wall above it. Look in the basement to see if there is a beam under it. If this wall is in the center of the house it is almost certainly load bearing. A door in a load bearing wall will have a header to carry the load to the wall below.

The note for the contractor to verify the hidden structure is a standard note. The important question is what is resting on the floor above. If there is another bearing wall, what is it supporting? Is there another floor or attic above it?

Sizing joists can be done from the building code tables. What requires some knowledge is determining the loads involved. A simple section drawing showing the joists and their supports is the place to start.

Looks like there is a beam in the basement along this line. I haven't opened it up, but it is protruding from the ceiling right in the same area, so I am assuming that this is the beam.
The floor above the kitchen is a deck, so no other wall above this one. If this is a deck, would the joist size be different (smaller) than it being another floor, like bedrooms? I am asking because the engineer was treating this as a ceiling joist, not floor joist.
Lastly, can we add a header (beam), instead of beefing up the joists? Could the wall below able to support the new posts for the beam or is that load too concentrated? It seems like fitting one beam snug under the joists is easier than trying to fit several joists snug under the floor. Am I completely off?
Thanks again!

"Lastly, can we add a header (beam), instead of beefing up the joists?"

Yes.

"Could the wall below able to support the new posts for the beam?"

Yes.

"Or is that load too concentrated?

No.

"It seems like fitting one beam snug under the joists is easier than trying to fit several joists snug under the floor. Am I completely off?"

It is easier; you are not off.

Thank you!

2x8s can EASILY span 18ft or more if they are for ceiling joists used only for uninhabitable attics with no storage, and are intended to only carry the weight of drywall.

If the 2x8s joists are planned to be floor joists for a new story above...you have problems.

one more thought--if the concern is that the new supporting beam will sit too low in your remodeled area, you can do a 'hidden' beam.
This involves building a temp wall on either side of where the beam will run, and then cutting each of the joists the width of what you are installing. You then push the new beam up into the slot you have created, post the ends, and then reattach each side of the cut joists to the new beam with joist hangers.

It is more work, but it reduces (and sometimes eliminates) the drop down of the new beam. We did this last year in a high-end kitchen reno, and as if worked out, the sized beam(lvl) fit completely up into the ceiling plane, the new posts (to ground) disappeared into the dining room wall, and the owners had a fully open kitchen, with nothing to show that a wall was removed when we were done.

The deck would create an additional load in a cold climate.

A beam would work if the support posts at each ends will sit on top of existing basement posts or the basement beam is strong enough to take the additional point loads or the basement beam is reinforced.

Why don't you use the approved drawings and build with 2x12's? Does raising or lowering the floor structure cause a problem?

Did the engineer visit the site and look at these conditions? If so, why isn't the 2x12 design appropriate to use?

Without knowing more about the existing conditions no one can advise you.