Basement floor is damp and the top of my foundation is cracking after air sealing the attic?
Horizontal cracking? That's odd, and I think that's unrelated to your moisture problem (even with a picture, I'm not sure I'd comment on that).

Well, you've air sealed your house, which means that now you have to actually pay attention to the V in HVAC: Ventilation. In a hermetically sealed house, I strongly suggest seeking a better filter system.

I'll take a wild guess that you lack a suitably sized fresh air intake for the furnace, as well as a make-up air inlet for the house (because most houses don't have either).

But you probably just need to look into buying a dehumidifier. Assuming that none of your power-vented equipment is over powering any of your gas-fired natural draft equipment, or that any other item like a fireplace is doing so (hopefully your CO detector will notify you of that).



Your A/C is over-sized or improperly charged. Have a tech come out to diagnose the unit. Hire whoever can explain the difference between superheat and subcooling to you, and what a wet-bulb temperature is.

And explain to them that, you need the A/C unit tweaked to run longer, whether it be from reducing the fan speed, or monkeying with the pressure to make it less efficient, with the goal being to drop out excess moisture from the air.

Central AC system not reducing the humidity in the air? –dslreports.com


  a standard AC unit will drop out more humidity the longer it runs - if it is oversized you will be too cold before it has a chance to do the job - the too large coil will make the air cold too quickly and the unit will cut off before it has time to drop out the moisture. A slower fan speed would help some because it gives the air more time at the evaporator coil and will let the unit run longer 


The thread goes on about relative vs. absolute humidity for a while...


  Going back to the OP, if the AC is cooling down the house too quickly, then open up some window shades [or room doors] and give the house some heat to force the AC to run longer. This will give more time for the AC to pull moisture out of the air and lower the relative humidity. Having a proper moisture barrier is important though. Never open a window or turn on an exhaust fan. By doing so, you are pulling humidity into your home and as it hits your cool air, it will condense and feed mold.


However if it's not all that hot outside but it's really humid, "Agreed with others in that you are sort of in the 'screwed zone'."