You don't have to have a basement if you don't want the reason he suggested that the new footing for the addition would have to bear on undisturbed soil, so they will have to dig down to the house footing, and with the walkout already there and the rest of the excavation for the new footing you pretty much end up with a full excavated basement.

If you don't want the basement, they will have to backfill and make a crawlspace or a slab.

IMO we do not have enough info as to why there is water there and IMO you need an architect to design additions not a contractor . Do you access this basement inside the house? IMO post some pics of the area from the outside .

Photos would help a lot.

Since you will be covering the outside stairway, if you extend the basement, you may not have a water problem. I would still put in the sump pump, just as a just in case. Sump pumps dont require a lot. It only takes a minute to make sure they are working, and if ever needed, you will be very happy to have it. I would extend the basement.

At the borrom of the stairway there is a typical drain that connects to the existing sump in the basement or to another drain source that will get rid of the rain water.

Depending on the age of the house this drains at that bottom of the staircases, in older homes connected to a dry-well, some to the storm sewer some even connected to a house sewer. Newer homes they would connect to a sump, dry-well or storm-sewer... In some cases they would have a a pit and a pump specifically for that drain.

So if this is an older home and there is no original exterior perimeter drain, the new basement would require to have a have a perimeter drain connected to the new sump-pump if it cannot divert ground water to the daylight without it.

You say you have a sump pump already, so the addition's drain tile can be tied to that (disregarding knowing where the existing stairwell drain discharges to).

You don't have to have it as an occupiable basement, but as GN described the foundation walls against the house will have to extend down to the basement level, and with the addition at only 6' out, probably the entire footprint. So at that point, you might as well make it another part of the basement. It can be a cold room, storage, or safe room if you only choose for a doorway to be cut into the existing wall.

Thanks for the responses. I'll try to get some better pictures tomorrow, but I'm attaching photos from the listing to give you an idea. The house was built in 67, but the walkup stairs are newer and there are drains in the bottom of the walls of the walkup that lead water to a drain in the floor. We are assuming there is some sort of french drain around the house, and that's where some of the water would come from for that drain. We are basically the lowest point in the neighborhood, so we get a lot of runoff from rains and the backyard stays pretty wet in some areas when it's been wet.

We don't know exactly where that drain leads to. The existing sump pump is at least ten feet away, and we have figured out that the sump pump leads to a nearby storm drain. We've already spend hundreds of dollars on the sump pump we have to upgrade it and to fix pipes that weren't connected properly, so the thought of another sump pump to worry about just isn't sounding fun, plus the basement itself has been full of bugs and small snakes (thankfully no rodents). We have to run a dehumidifier spring through fall to keep the bug population down. More square footage to worry about down there just seems like more space to get annoyed with.

So what I'm understanding from the responses is, is that the addition would have to have a foundation at the same level as the basement? We just weren't expecting that I guess. I was also hoping there would be an easier way to divert water away from the house, but with the basement basically completely underground, and the house not being that much higher than the yard, there wouldn't be a way to move that water without a pump.

I guess what I want to hear from someone who knows what they are talking about- is adding a basement room under the bump out the best option? Or is there something my contractor hasn't considered that might be a better option?

(not sure if this makes a difference- but part of the bump out will be two stories to bump out the master as well)

A design professional might be able to help you with your addition plans. Typically, bumping out only 6' means you want to extend your existing spaces, not create new fully separate spaces. However, you will have framing needed to support the existing upper floor, which would most likely still delineate a split between existing and new spaces, which is not optimal. There also are some design points about how close your bumpout gets to the cantilever bay, and the roof tie-in on the side wing of the house.

You might be missing the gist of why a basement is being proposed. You have an exterior stair dug down to basement level where there is no 'dirt' in that stairwell, it is all open. So after removing the stair, you have a blank space down to the basement level. The new foundation will need to extend down to that same basement level, because you do not want to place a new crawlspace or slab on top of new 'dirt' backfill. And, since you are only wanting to extend out 6', 3'+ of which is already excavated, to excavate the other 3' for a change in foundation wall height is inefficient. It is much easier and cheaper to just extend the dig out at basement level for the full 6' addition. Thus, you have a big empty box the height of your basement, so why not utilize it since you have it.