Two years ago at my father-in-law's cottage we constructed a 16x24 garage on a slab of concrete (4 to 6 inches thick on a sand based ground) with a R20 insulation value for the walls, vapor barrier and aspenite interior that was painted. Lots of insulation in the roof cavity. It has a 10x8 insulated garage door and 1 window. We find that the interior has a great amount of humidity and we are thinking to use the idea of a non condensing dehumidifier system by putting a 8 inch round duct with a fan inside it (sold as a complete unit). It would be 4 to 6 inches from the garage floor and would be vented outside: would this work? If it would, would we need to put a fresh air vent at the opposite side of the duct to replace the moist air that the fan would remove from the garage? If not can you suggest a treatment for this problem that is causing the walls to sweat and tools to rust.
Answer:
Don't worry about it. There is no way you'll create a vacuum in there. Ventilate, ventilate, ventilate. As long as you have a humidity problem you have rusty tools and all kinds of other moisture problems.
