Humidity problem

My barn tends to run on the humid side. It is particularly troubling in the early spring when the barn is still cold, and the air is warm and moist, but year round the humidity levels are high. I live in SE Michigan.

It is a 44 x 54 building with a concrete slab. On top of the slab is a VCT floor. The roof is trussed with ply and asphalt shingles. It has a ridge vent. The interior ceiling is OSB and there is R19 batt insulation, vapor barrier down on top of it. The walls are OSB with batt insulation behind them. Not sure if it is R13 or 19. The garage door is insulated 10x10.

There is an "attic fan" in the ceiling that when active draws air out of the conditioned portion of the barn, into the attic and out the ridge vents. I do not use this as I think it would draw humid air into the barn.

In the summer it is generally cooler in the barn then outside by quite a bit. (today it was 70 degrees F in the barn, 86 F outside. Relative humidity in the barn was 60%.

Because the barn is cool, and the air is moist I have condensation issues. When it is particularly bad, the floor and cars can get damp. I have had a mold grow on the interior of one of my cars last year. In response I added a portable dehumidifier and it does help, but is not doing enough, relative humidity is generally high.

If I open the garage door on a humid day, everything in the barn that is metal (like my cars) gets coated in a fog of condensate. I am tempted to run the heat to warm the barn up and reduce relative humidity, but It is hard for me to actually do that when it is 86 outside...

Would an fan in the attic to outside on a humidistat help any? More or larger dehumidifier? More roof insulation?

Suggestions are appreciated,
Joe

You need something like this or the max dry. http://www.santa-fe-products.com/products/impact-xt.html

The little dehumidifiers are sized for 100-200 sq ft. You have 10x that and thus need something that can get enough air through it to make a difference.

While not a garage my ~1500 sq ft basement with 9' ceilings (it's about total volume not just sq ft) was at 60-70% humidity. I installed the unit from the link and 2 days later it's holding steady at 45%.

Warming up the air will reduce the % but the total water in the air will still be the same. Thus your best bet is to condition/ cool the air, which removes humidity or install a dehumidifier of size to handle your space.

I have a similar issue and it's sort of a loosing battle.
Live in the woods in the shade.........garage floor condensates any time the dew point is above 65-70*. There is not stopping it and no cure. It a garage that is used every day and trying to condition the air space is not practical. The garage floor remines cool the entire summer. It similar to a ice tea glass.......no way to stop the glass from sweating.

I do have a separate shop with the same condition.........BUT.........the doors are not open often or for very long periods of time and it can be 85-90* outside and the garage temp will be 65-70* . Both spaces are very well insulated.

I had the same problem. The Santa-fe Advance 2 worked for me. You have twice the size building so I would recommend 2.