If the garage floor has condensation, it’s likely that the builder did not install a vapor barrier before pouring the concrete. A vapor barrier can be as simple as a 4mm or 6mm plastic sheet spread across the floor and properly sealed at the seams and other openings. The vapor barrier, also called a vapor retarder, prevents water vapors from condensing by allowing them to pass through the material.
It’s probably not feasible to tear up the garage floor and install a vapor retarder or install radiant heating in the floor; these are expensive options. Try running a humidifier, which will pull some of the moisture out of the air.
Find out what the codes are for the installation of vapor barriers in your climate. Vapor retarders can also be installed on walls and ceiling. Some insulation materials have the vapor barrier attached. If insulation is installed in the walls or ceiling and the wrong type of insulation product is used or install improperly, you can end up with moisture issues.
Also, ventilation is very important to ensure the proper air flow and keep the proper balance between interior and exterior temperature. If the garage is not properly vented, there won’t be a path for moist air to escape. Check that the proper vents are in place and are open and not obstructed. The ridge vent should be in the roof.
There may be a series of small vents along the roof or one continuous vent large enough to ventilate the entire space. Also, check for soffit vents or vents installed in the lower part of the exterior sidewalls. Another ventilation option is an electric-powered vent fan, which operates on a timer system.
If condensation is forming on a finished garage ceiling, it may be an indication that the cavities between the rafters were insulated. If the job was not done correctly, this could be the source of the problem. A case in point -- ventilation channels were not installed between the insulation and the roof sheathing.
Do not vent the dryer or other exhaust to the garage. This can cause excess moisture; always vent exhaust from appliances and exhaust fans to the exterior. This will avoid moisture problems and avoid potentially costly repairs.