I am looking for advice on the best way to reduce humidity seeping up from my unfinished basement floor of my large, Second Empire Victorian house in Western Massachusetts that was built in 1882.  The basement is unconditioned space.  The basement walls are fieldstone and then brick foundation. Part of the basement floor is concrete, and part of it is Rat Slab (see photo below) that has lots of cracks through which humidity and moisture percolate up.  The concrete floor is usually dry but sometimes it’s damp or wet which I suspect is a combination of condensation and in a few places where there are cracks water seeps up from the ground.

I have two good French drains along some of the walls each with its own sump pump, although where the French drain is, the stone was never cemented over (see photo below). Along key parts outside of the house I had grading done in which rubber was installed three feet below grade and then drainage pipes and stone. The drain pipes take the water far away from the house.

I think I need to install 1.5” XPS foam insulation board on the part of the cement floor where condensation and seepage occurs.  I can’t decide if I need to have a dimple mat directly on top of the cement floor, and then have the insulation board, and then I’d have cement board for the floor.

Another option I’m thinking of is to cut ¼” channels in the 1½” EPX foam insulation so that if there is water that comes up through the floor it will have a channel to flow through.   If this insulation board with the channels extends over the stones of the French drain, then the water would be carried away.

Has anyone ever done this:  Cut ¼” inch channels in EPX foam board which is then put on a cement basement floor?  There is a product, Dricore, which is insulation board with ¼” big groves and then on top of it is Oriented strand board (OSB).  Dricore is expensive.  It will be less expensive to install 4’ x 8’ XPS rigid foam board and cut groves in it, then buying Dricore.  What do you all think?

For the Rat Slab part of the basement, I plan to install another trench drain where the fieldstone foundation meets the floor, and at the lowest point of the Rat Slab. I plan to cover the Rat Slab with 20 mil polyethylene, making sure the edges are sealed down. I don’t think condensation collects on this part of the basement floor.  Does this make sense?

Attached are photos of the Rat Slab, and the concrete floor that some times is wet from condensation and water seeping up occasionally and in this photo you can see the stones of the French drain.