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We have a small house and a lot of stuff (camping gear, winter coats, books) is kept in a storage facility. The place we had first was very humid, then I bought a hygrometer and found another space.

The hygrometer measured 80% humidity in the new place when I left it on the floor, which is just tarmac. I though that this is too humid to move there. Is it wrong to put it on the floor and should I instead have put it on something?

Then I found yet another space, moved stuff from the original humid storage to the new place which is on the first floor of an unheated storage facility. This time the hygrometer read 75%. This reading is also from the floor and I had filled the space with stuff coming from the original storage. I have no reading for the humidity there but I did hang a cotton bag with about 1.5kilo of salt there, and it was dripping.

Is it possible the humidity at the newest place is in fact from my stuff, and the storage itself would be ok? Is it wise to put the hygrometer on the floor?

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    Concrete is inherently wet (ask a wildfire victim about the prospect of reusing their foundation, and you'll hear an earful about how removing all water from concrete kills it). Water also transmits through concrete. So unless the facility was laid with vapor barriers, I would say you are getting bogus readings. Heck, lay a sheet of plastic across most concrete floors and you'll see condensation on the plastic! Dec 1, 2021 at 0:13
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    Is it wrong to put it on the floor and should I instead have put it on something? ... what is preventing you from making multiple readings at varying heights above the floor?
    – jsotola
    Dec 1, 2021 at 1:30
  • @Harper-ReinstateMonica the floor is actually tarmac, black, like road. I have no idea is that changes anything.
    – Ivana
    Dec 1, 2021 at 22:16
  • @jsotola Time? I have a job and family and can do better things with my evenings than drive around to experiment with hygrometers.
    – Ivana
    Dec 1, 2021 at 22:18

2 Answers 2

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"unheated storage facility. ... hygrometer read 75%."

Yeah, that's pretty much shockingly normal. An unheated storage facility is hopefully not getting rained in, but otherwise there's no particular reason for it to be low humidity unless you are in a naturally dry climate.

Check the weather history at the nearest airport (or other weather station) for outside humidity, and don't expect better than that, unless you are in climate controlled storage. My local airport shows a high of 100% and a low of 65% with most readings in the 80's and 90's over the past 3 days.

"Dehumidifiers" along the lines of the "bag of salt" have no hope unless the space is completely air-sealed, which is very unlikely in unheated storage units. More damp air will just move right in.

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    Right, you are better off packing your possessions in boxes and lining the boxes with large plastic bags. Throwing a dessicant pack inside the bag wouldn't hurt either. They make proper dessicant, that can even be recharged in an oven (hold it slightly over 100C for an hour, the moisture boils off, then put it in a plastic bag to stop any absorption until use). I don't know what that business with salt is, but it sounds like hillbilly nonsense... salt air is highly corrosive so I wouldn't let that near any stuff I valued. Nov 30, 2021 at 23:57
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    Take a few boxes of stuff from the storage unit home. Let them dry out for a week or so, pack and SEAL them at home in the reasonably low humidity inside a conditioned house, then return them to storage. Bring home a few more boxes. Eventually, everything will be packed and sealed with dry(ish) air inside plastic and all the items will be protected. After that, it doesn't matter what the humidity level is outside the sealed packages.
    – FreeMan
    Dec 1, 2021 at 15:13
  • Of course Bayes! I should have asked myself what the expected humidity would be.
    – Ivana
    Dec 2, 2021 at 22:44
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The best place to put a hygrometer is at the top of the house and away from any windows or doors. The reason for this is that it will give you an accurate reading on humidity levels in your home without being affected by external factors such as wind, rain, snow, or sunlight. On most occasions, the hydrometer is hung on the wall, and it should be at least 2' off the ground to avoid making false readings.

For better results, a good rule of thumb is to try to keep the temperature of your home between 65-80 degrees Fahrenheit (F) when taking the reading. For the intended storage area, the acceptable temperatures should remain lower than 68 degrees F, with relative humidity between 30 and 50%. Fluctuations should not exceed +/- 5 degrees F in temperature, and +/- 3% relative humidity within a 24 hour period.

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  • Since it was noted that this is an unheated storage area, I doubt the OP is going to have much control over either temperature or humidity.
    – FreeMan
    Dec 1, 2021 at 15:11
  • @FreeMan If you want to store your item in a non-weather control, unventilated warehouse, or even your own bathroom, nobody will stop you. It is up to you.
    – r13
    Dec 1, 2021 at 16:06
  • @FreeMan The focusing question is where to place the hydrometer.
    – r13
    Dec 1, 2021 at 16:08

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