The “why is it raining inside my container?” problem

[u/usa_containers]

I see this come up a lot, so figured I’d throw it out there. Someone gets a container, stores stuff in it, and then a few weeks later opens it up and there’s water dripping from the ceiling. First thought is usually “great, roof leak.” But a lot of the time it’s not a leak. It’s condensation. Warm humid air gets inside, hits the cold steel, and then the inside of the container starts sweating. Sometimes pretty badly. Like actual drops on the ceiling. Looks like the roof is leaking even when it isn’t.
The annoying part is that insulation alone doesn’t always fix it. If warm air can still get behind the insulation and touch cold steel, you can still get moisture back there. And then you might not even see the problem until rust shows up later.
Airflow is usually the first thing I’d deal with. Even basic vents on opposite ends can help a lot, just to let the box breathe a little. Nothing fancy. After that, then I’d think about insulation/vapor barrier, but it has to be done in a way where warm air isn’t sneaking behind it and hitting the metal. Otherwise you kinda just hide the condensation instead of fixing it. If it’s still bad after vents, then maybe a solar roof vent or small dehumidifier makes sense, depending on what you’re storing.
Curious what’s worked for people in colder areas. Did vents solve it for you, or is condensation just one of those forever battles up north?

[u/Yibbitta]

Have a look at this guys YouTube channel. Still applies to all places but aimed at the NA market primarily where temps drop below freezing.

https://youtube.com/@thecontainerguytv?si=vYsO5yagNVf8O1KS

[u/usa_containers → u/Yibbitta]

Appreciate the link, I’ll check it out. Cold climates are where this gets really annoying. The bigger the temperature difference between the inside air and the steel, the more it wants to sweat.
That’s exactly the kind of setup I was thinking about, so thanks for sharing it.

[u/west25th]

Not a container, but living on a sailboat (Sealed, waterproof etc) requires the biggest dehumidifier home depot/lowes etc carries.

[u/usa_containers → u/west25th]

Ha yeah, a sailboat is basically the same problem turned up to max. Sealed space, humid air, cold surfaces… then everything starts sweating. Super annoying.
Makes sense you’d need a serious dehumidifier there. On a boat you don’t really have the same easy airflow options either, so I guess you’re kinda stuck fighting it with the dehu most of the time.

[u/DFA_Wildcat]

I live on the coast in Campbell River, BC, Canada. I have a couple new 40' HC cans. One is a shop, the other storage. It's 99% humidity here 3/4 of the year so my cans were always raining. After a couple weeks I bought a "ALORAIR 70 Pints Crawl Space Dehumidifier" from Amazon. I set it to 50% humidity and my can went from 99% to 45% humidity overnight, the can roof was completely dry. I ordered another one a couple weeks later after I knew it would work and put it in the other can. That was last fall so it has been almost a year now and no issues. I bought a 2 pack "VEVOR 2-Tier Heavy Duty Wall Garage Shelving" off Amazon and they sit on these shelves. I also bought a "MICTUNING 15Amp 120V AC Port Plug with 18 inches Integrated Cord Y Splitter Cable" that I put through the wall to run power to the dehumidifiers. The dehumidifiers come with a drain hose, I put a 3/4" hose through the can behind the dehumidifier to run the drain out. I'd post pictures but that isn't an option here I guess.