Humidity in my detached concrete garage

[treblediva]

My garage is a detached concrete block structure that is recessed into a hill on three sides. It's also intended as a tornado shelter, so it's VERY sturdy. It has an attic area that has a floor for extra storage.

My home is in the greater Atlanta, GA area. Humidity is a huge problem here, both in the cold winter and blazing summer. Pretty much anything stored in the garage will eventually be subject to mold-- even the vehicles, if they are not sealed up tight!

My goal is storage for excess household/outdoor items, canned goods & long-term food storage and a small workshop for woodworking/car repair.

Any advice on the following is appreciated as well as thoughts I haven't expressed:
1. I expect, eventually, to be heating/cooling to control the humidity. What are the bare minimums for each? (I'm shooting for <50% humidity, if possible.)
2. How do I insulate the concrete block walls? The garage door?
3. Do I need to ventilate the attic roof while insulating?
4. I want to install walls in the attic. Which is better--OSB or drywall?
5. What is the best/least expensive way to climate control/ventilate the two different layers?
a. Bottom floor=3 concrete walls below grade and garage door.
b. Attic=all above grade and hatch to bottom floor.

 

[914wilhelm]

I might place some plastic sheeting up against the walls and floor in an attempt to figure out how much of that humidity is coming through the walls and floor. If there is a lot of water coming through, you may need to excavate the walls, tar the outsides and place drains at the bases. Also it is good to slope the dirt away from the walls to decrease water pooling against the walls. If the walls are dry then I would work on running a dehumidifier indoors. If the walls are leaking water though, a dehumidifier will be a losing battle.

 

[Randy in Maine]

If it were me, I would have the local spray foam guy shoot 2-3" of closed cell high density foam on the CLEANED interior concrete walls and the roof. Assuming this thing was built to not allow for moisture to wick through the concrete, I would think that would act as the vapor barrier.

I would then use a properly sized air conditioner to remove the excess humidity and provide for some cooling.

A mini-split would be really worth having.

 

[matt_i]

There is a type of paint designed for aiding waterproofing of concrete block. I would try that first. The dehumidifier is next, I would also get 1-2 ceiling fans and keep them on low speed, moving air despite being humid, will not allow mold to grow easily. Couple it with the dehumidifier and it will dry out.

The A/C would be another way to dehumidify but also include the benefit of cooling the space for greater comfort.

Personally I would let the attic be "hot" meaning ambient (+) and passively vent it with soffit and ridge vents. Keep your items needing climate control downstairs and separate with a drywalled ceiling plus fiberglass or similar insulation.

 

[rsanter]

There is a type of paint designed for aiding waterproofing of concrete block. I would try that first. The dehumidifier is next, I would also get 1-2 ceiling fans and keep them on low speed, moving air despite being humid, will not allow mold to grow easily. Couple it with the dehumidifier and it will dry out.

The A/C would be another way to dehumidify but also include the benefit of cooling the space for greater comfort.

Personally I would let the attic be "hot" meaning ambient (+) and passively vent it with soffit and ridge vents. Keep your items needing climate control downstairs and separate with a drywalled ceiling plus fiberglass or similar insulation.

This

Bob

 

[DC73]

Given your location and unique building situation, I would post your questions on the Q&A forum at GreenBuildingAdvisor.com They have some building science gurus who hang out there. It would be good to hear what they have to say.

DC