We've been in our house a little over a year. This spring a damp spot appeared (it wasn't there before) in the concrete floor of our under-house garage. And it hasn't gone away. We have no idea what's causing it and pondering it has left us baffled.

The spot is about 3 feet in diameter, off center in the garage floor. It's not near the walls or window. The floor is unpainted concrete and there are no pipes nearby. And most importantly, we don't even part our cars in there. It's more of a work space than anything and is mostly empty.

My first thought was a wet spring, some water crept in from below. That theory got scrapped when I moved a few items that were in the area and found that underneath the boxes and bags was bone dry, leaving nice outlines of the items in the midst of this damp spot. This said to me, it must be coming from above then. But the ceiling is dry and shows no signs of water, past or present.

My only other theory was that the window had been open (on the opposite side of the garage) and for some reason the morning air was condensing on the floor. Settling dew would explain the dryness under things, but why only that one area? I closed the window weeks ago. Yet the spot continues to mock us.

I'm out of ideas. I'm hoping the good folks here can offer me some explanation for this oddity and let me know if it's something to worry about or ignore as part of the house's "charm".