Iv'e been fighting this present issue for a year now with no results from my prior havc instructor and hvac co workers. I live in seattle, wa in a 1700 sq ft rambler with an underground fully finished basement ( drop ceiling). My wife and I and my 2 kids occupy it about it about 14 hrs out of the day. I have 2 baths on the top floor and 1 in the basement, all have high cfm EH fans which are used. The bath down is plumbed to an in ground sump and ejected into the mainline. (main sewer line is higer than the lower bath). The house is a 1947 which I fully remolded - with double pane insulated windows and min r-30+ in the attic with code roof vents. Heating is an 80% 70kbtu gas furnace and 2.5 ton condenser.
Last year my wife calls me at work and says there is some water in the mechanical room comming from the hot water heater. I had her turn off the water main comming in the house , which is located down stairs in the drop ceiling until I got home. I found the newer supply line had broke and replaced it. When turning the main back on I noticed a green stain line which ran down the wall where the shutoff is located. I also noticed all the copper which was insulated fully condensing. I removed all the insulation, wipped all the piping and checked for leaks, both with the water meter on and off- no leaks. Mind you this is in the wineter months here with alot of rain. I put the basement in 10 years ago which has a continous footing drain and has never leaked. I bought a portable 35 pint dehuhidifier and attempted to investigate further. I replaced the sump gasket, replaced all 3 closet rings on the toilets. The dehumidifier has run constantly both during the winter and summer for the last year. I run my ac from may to oct also. Humidity is 55-60 all the time regardless if I run the unit in auto or on. Like stated before the house is pretty insulated and tight. I don't pull in any make up air, since majority of the months the ouside is raining and don't want additional humidification brought in.
Any ideas that can be brought to light would be much appreciated.