Subfloor Void - No Ventilation

[CENTHOME1912]

Hello All - First time posting here! I have a suspended floor I am working on and need some advise. I am building on top of a sloped concrete pad. Because of the sloped pad, the 2 x 8 joists will be sitting on top of the vapor barrier (plastic sheeting) on one end, and on the other end the bottom of the joists will be suspended above the vapor barrier by about an inch and a half (40mm). I am going to install 1-1/2" XPS rigid foam board directly on top of the vapor barrier (between the joists) then fill the seems against the joists with spray foam. Because each bay will be "sealed" I will not have any ventilation running under the joists and cannot run a dehumidifier, short of running one in each of the joist bays. What is typically done in this scenario? Do I need ventilation? Or because I am using a vapor barrier and XPS rigid foam board, along with the bays being "sealed" I do not need ventilation? Will there be condensation from the warm air in the house vs the cooler air in the joist bays, or will the air naturally get to an equilibrium? Thanks!

 

[blup]

Where is the existing ventilation if any?

 

[CENTHOME1912]

There is no ventilation.

 

[Deluks]

There is no ventilation.

Are there any exterior walls?
Trapping timber underground without ventilation will not end well.

 

[Scally-Ho]

Is it possible to duct outside air via plastic soil pipe to the void? As soon as the dew point is reached in the void, condensation will form.