I have a garage that lies in sloped terrain with the back wall almost fully below ground level. The garage is very moist, probably because of water seeping through the walls and floor.

I would like to build a small metalworking shop in the back of the garage. The shop would need to be reasonably dry to avoid rust on equipment. I have thought about building the shop almost like a shed within the garage, with a few inches of air between the garage walls and floor and the shed. The shed will have to be insulated because of temperatures below freezing in the winter.

Is this at all possible without digging around the outside of the walls and fixing the drainage?

  • Ideally you want to insulate the outsides- but you can insulate the inside walls.. and drain the water at the bottom somehow and build a new inner wall.
    – Piotr Kula
    Commented Aug 21, 2011 at 20:46

2 Answers 2


This might not be the answer you are looking for, but depending on the amount of moisture in the garage, why don't you just run a de-humidifier? I have one running in my basement, which gets very damp without it. I bought the one with the smallest container, since I'm bypassing the bucket with a garden hose straight to the floor drain. I have mine set a little high at 70% since that seems to be the threshold to the bad smell that comes from a musty basement.

If you get a newer, more energy efficient model, you will save money on your electric bill. Not to mention, it will probably be cheaper than your other alternatives.

  • This would only require building a wall to make a closed off room at the back. The de-humidifier would give some heat also. I think I will try this solution first. Commented Aug 22, 2011 at 8:46
  • Give us an update when you have done it all
    – Tyler
    Commented Aug 30, 2011 at 3:44

The major cause of rust on machine tools is fast changes in temperature during humid weather.

Imagine this scenario: you have a large pile of steel sitting in your cold garage at night. Because the garage is dug into a hill, if the garage is well-insulated, the temperature of the steel will be near the ground temperature, probably around 5 C. During the afternoon, warm, humid weather arrives, and you decide to go out to the garage to do some welding. You open the door, and a breeze of 20 C, humid air blows into the garage and hits the cold metal.

Cold air can't hold as much moisture as warm air. When the warm air hits the cold metal, the air is cooled. (The metal also warms up a little, but more slowly.) If the air is humid enough and cool enough, condensation forms on your steel. That's when you get rust.

To prevent rust, you need to do two things:

  1. Reduce the permeability of the garage to air.
  2. Regulate the temperature of the garage with heater that has a temperature sensor of some sort.

You can try a dehumidifier, but for the cost, I suspect that a heater is a better deal.

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