Background: I had high Rh in crawl space with associated mold/mildew/etc. damage in crawl space as well as 1st floor of home.

Action: Installed new gutters and extensions. Made sure condensate lines for air handler (in crawl space) vent to outside. Made sure that sump and "spyder drains" operating properly and vented to outside. Had crawl space professionally encapsulated (looks like very thorough job) New insulated wall to isolate crawl space from wrap - around porches, etc. Had a high quality dehumidifier installed that vents to outside. Installed two transmitting humidistats in crawl space that transmit to data logger that also monitors indoors and outdoors temp and Rh.

Results: Crawl space temp runs a constant -5 degree f below 1st floor of house. Crawl space run a constant 50-55% Rh. House runs constant 65 degrees temp. House runs a fairly constant 35-40% Rh. Outside has ranged from 25 -65 degrees F and 30-85% Rh.

Puzzle: Obviously dehumdifier in crawl space brings Rh down to the set point of 50-55%. Temperature of crawl space behaves as expected vs. house. BUT when inside is 30% Rh and outside is 30% Rh for several days, the crawlspace is always 55%. The dehumidifier brings Rh down to the set point but WHAT is raising the Rh above 55% if inside house and outside is 30%.

I suspect that some type of inflitration of water is still occuring to raise the humidity in the crawl space but my contractor says that the system is performing as I should expect.

I would love to hear some discussion on this topic and why crawl space runs 55%.