Moisture on shop floor

[Jeff720]

I have a 25x35' steel tube shop with a 6" slab, built in the PNW. I have 3" spray foam on the ceiling and 2" rigid foam on all of the walls. It also has two 10x10 roll up sheet doors, the tops have a brush seal, but the sides do not.

I can barely register any moisture with my meter on the ceiling or walls, but the floor is consistently wet. I do have gutters installed and a vapor barrier was installed under the slab. The temperature on the walls and ceiling is about 1-2 degrees warmer than the floor when the doors are all closed.

I'm wondering if it needs some venting now that I have it sealed up pretty good.

Any help would be appreciated!

 

[Showkey]

Measure the indoor shop relative humidity..........suspect it’s 70-95%.

The floor is likely condensing the moisture in the air. The floor is acting like a giant ice tea glass on hot humid Summer day.

The answer is warm the slab, warm the air space, limit the air exchange rate and lower the indoor relative humidity while maintaining the indoor temperature.

Running dehumidifier will help if you have control of the temperature swings and seal the doors ( aka lowering the air exchange rate.). You paid for spray foam but the leaking door is counter productive. Dehumidifier work best at 50* plus to avoid prolonged defrost mode.

The goal in “winter” might be 50% indoor relative humidity. Remember the relative part is it’s relative to the indoor temperature. Add indoor heat ( vented) lowers the humidity levels. PNW and humidity is a challenge year round.

 

[fitter30]

Take piece of tin foil duct tape it to the floor for a few days take it up. Wet on top coming from the air between foil and floor coming from floor

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