Basement damp and water intrusion

[Tony Wang]

I have a property in Seattle with a basement apartment. It is below grade and built from a crawlspace (still have half of the crawlspace remaining). The previous owner likely did not do it properly because it is a nonconforming basement.

The emergent issue is that the basement is pretty damp. The humidity level is always 70 to 80. Running a dehumidifier helps but then I cannot open the windows. It has the basement smell or the damp smell, which may likely cause mold issues but I haven't seen anything obvious yet. I don't see water intrusions no matter how heavy it rains. However, when it snows heavily which is once or twice a year here, I could see the water coming in from the cove joint.

I talked to two foundation companies. Both of them suggested burying a sump pump in the basement to deal with the water intrusion, and the damp issue will go away after that. However, it doesn't seem to be a good idea to do anything inside the basement according to the posts I see here, and I don't know how that can magically resolve the damp issue. Any suggestions on what to be done, and where I can learn more about this?

Also, who should I talk to, a foundation expert, a basement expert, or a GC? Any local recommendations are appreciated!

PS: I am also looking to get it up to code and maybe add an egress window on the other side as it has no natural light coming in. Is this something that can be included in the same effort?