I have and 1841 house with granite basement. What is a normal humidity level I should control it too?

Question

I would like to prevent mold from growing. I live in CT in an old house, the basement does not leak but gets very humid.

Answer 1

A wet towel should be able to dry down there.  there are small round aluminum vents with screens in them that can easily be put in opposing walls between the joists,  It takes just a hole saw and drill.     A cellar that smells damp is too damp.  On them vents.  It is good to plug them up in winter as too much heat will leave.  Summer is the time of most humidity problems particularly if you have a cellar furnace.

Answer 2

Depending on the accessibility, you could install a bathroom vent fan in your basement exhausted to the outside.  You could run it on a timer so it would run a couple hours a day automatically.  You could also install a dehumidifier near your sump pump if you have one and modify it with a drain hose that emptied into your sump system.   A 'good' humidity level would be 60% RH.  

Granite can also contain radon.  If there is alot of granite, spend the $20 for a radon test kit.