Damp garage, need suggestions

[homerj]

Hi folks, recently moved house, garage is sectional concrete panels with corrugated roof, slightly oversized concrete floor with potential dpm below which doesn’t go back under concrete panels, garage is watertight but floor is wet below car and underside of car was wet,
Heating hasn’t helped due to no insulation atm so currently running a fan under car which has dried things up.
Dehumidifier showed 75% this morning when turned on and hasn’t brought humidity down by much,
Is this purely a ventilation issue, no problem adding some vents but would also like to be able to get a bit of heat in there

 

[RrogerD]

Likely wet due to condensation (cold floor) rather than rising moisture. Not a lot you can do about it tbh without digging out and re-laying with insulation.
In general, garages were built to house a vehicle rather than storage things and so keeping it dry from above was the primary aim rather than having warm 'feet'.