How to address high humidity in downstairs rooms

I am throwing this question out hoping someone else knew where to start with this issue- the rooms in my downstairs have high humidity (60%) and the house is built into a hill with a crawl space underneath. I am using a de-humidifier but worried about all the moisture/mold. Who would I call to check this out? Thanks for any help! 

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I had Cheryl from Mold Busters come to our old house to check out the lower level. She takes measurements in the rooms and lets you know if there is enough mold to have to do something about it. She was great! https://moldbusters.net/

We had the same 60% humidity on average in our bungalow (not on a hillside) along with general moldiness in the house. Years ago, we installed a vapor barrier over the dirt in our crawlspace and sealed at the sides of the foundation. We also added an energy efficient small "low sone" bathroom fan in the basement wall to run 24 hours a day and gently pull fresh air thru the space. You might also look into creating bigger air openings in your crawlspace if they are too small, as is the case in some older houses.

That combo has been effective at getting our humidity reading down to 50% on average. We also installed HEPA filters inside house that help with any residual mold. 

You can research vapor barriers online -- people who are up to crawling in the crawlspace can do it themselves; otherwise hire a contractor. There is a small ongoing energy cost to adding a fan to keep the air moving, but for us it is worth it.  If you buy HEPA filters, check on their power draw as it will also add to your electric bill and get an energy efficient model (we went with BlueAir).

Over the years, we've also used the SF firm Healthy Building Science to do some mold and indoor air testing, which was informative in our case (they are one of several health building consultants around in the bay area). They could probably recommend contractors to do crawlspace work.

There are also contractors who advise enclosing and sealing the whole basement. While that might be required in some situations, it is super expensive. Good luck with your decision.