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?

[Marcus Auerbach]

We deal with this a lot in Milwaukee, even tough our basements are built differently, the principles are the same.

First line of defense is surface water management: gutters, down spout extensions and grading. The soil around your house should always be dry when you take out a scoop with a shovel. If your soil is wet, your basement will be too.

A sump crock is the next step, as it helps get water out from under the house. In Wisconsin houses have an inner and an outer drain tile system, basically a pipe with holes that runs around the foundation and collects all the water and then guides it into the sump crock, from where you can pump it out and discharge far away from the house.

A dehumidifier is your last line of defense, but if #1 and #2 are done correctly and you have proper ventilation (install a super quiet high CFM fan on a humidity switch) you should get down to pretty low levels.

You want to talk to a basement contractor, they specialize in foundation and water issues and have the crews to deal with it.