The condensed version
I pulled into the garage yesterday afternoon, and the floor was soaking wet. This is not the sort of sight that delights a homeowner, so I spent the next few minutes looking for an obvious source.
Now I’d seen damp spots in there before, but nothing like this, except for those few times when we’d had a combination of heavy rain and winds at the precise angle to drive water in under the garage door. Inasmuch as we’d had an unusually-dry December, this wasn’t the explanation. There are water lines out there, this being where the laundry equipment is housed, so I inspected them. And it occurred to me: were the lines leaking, wouldn’t it be wetter nearer the lines? Yes, it would; and no, it wasn’t.
Finally it hit me. The first half of the week had been seriously cold. (Sunday’s high was 27, Monday’s 28.) Things gradually worked back to something resembling seasonal norms, and then Friday, out of the blue, we had 70s all day. So I formulated a hypothesis: the concrete slab on which the garage stands had been so thoroughly cooled for so long that when the temperature reached the 70s — with a dew point hovering around 60 — massive amounts of water vapor condensed on that cold, cold surface. What’s more, said surface, I reasoned, should be warmer where it’s closer to the rest of the house, and yes, it was drier.
So I put the matter out of my mind and went in to listen to the basketball game. Then about four this morning, there was an exceptionally-loud thunderstorm that dropped half an inch of rain, the result of a cold front running smack into that mass of warm air; at the moment, it’s in the upper 30s, and the garage isn’t even slightly damp, except for a square of carpet that absorbed a fair amount of water yesterday. Lesson learned.
Jason »
27 December 2008 · 9:40 pm
Well, that answers my questions about our semi-closed-in tiled front porch that was soaking wet the other day also.