Why is my shop so humid?

[zmoz]

I have a shop built out of concrete blocks with a concrete floor. Ok, the seal around the door isn't 100% perfect, but why, oh WHY is it always so humid in my shop? It is often in the 70-80% range, about the same as outside. I use a dehumidifier in there but it just can't keep up with the amount of humidity coming in. There is only a little bit of insulation in my roof, and the temperature stays around 50 degrees. There are only two openings in the concrete blocks, one for the man door, one for the roll up door, and they're usually closed.

On the other hand, my garage, attached to my house, has no humidity problem at all. It stays below 50% almost always. The two buildings are very close, why the difference? My garage isn't insulated and the seal around that door is even worse than the one in my shop. I've never used or needed or even thought about a dehumidifier in there.

Is moisture seeping in through the blocks in my shop or something? It's really pissing me off seeing all my stuff get rusty. Really the only difference between my shop and my garage is that the garage is wood framed, the shop is concrete. The garage might have some kind of vapor barrier in the wall, but there is still plenty of gap around the roll up door that could let moisture in. Why no humidity there?

 

[EMS503]

I had a similar problem in my basement, I cured it for the most part by leaving a fan blowing to circulate the air in the room.

 

[zmoz]

I had a similar problem in my basement, I cured it for the most part by leaving a fan blowing to circulate the air in the room.

Yeah, I've usually got a fan running too. Doesn't seem to help much.

 

[jbooth]

I have the same problem with the floors in my shop and attached garage (both unheated). On certain high humidity days both floors become completely wet. Generally just happens in the spring. I have always attributed the warm mosist air hitting the cold floor and drawing the moisture from the air.

 

[SandburRanch]

I have a shop built out of concrete blocks with a concrete floor. Ok, the seal around the door isn't 100% perfect, but why, oh WHY is it always so humid in my shop? It is often in the 70-80% range, about the same as outside. I use a dehumidifier in there but it just can't keep up with the amount of humidity coming in. There is only a little bit of insulation in my roof, and the temperature stays around 50 degrees. There are only two openings in the concrete blocks, one for the man door, one for the roll up door, and they're usually closed.

On the other hand, my garage, attached to my house, has no humidity problem at all. It stays below 50% almost always. The two buildings are very close, why the difference? My garage isn't insulated and the seal around that door is even worse than the one in my shop. I've never used or needed or even thought about a dehumidifier in there.

Is moisture seeping in through the blocks in my shop or something? It's really pissing me off seeing all my stuff get rusty. Really the only difference between my shop and my garage is that the garage is wood framed, the shop is concrete. The garage might have some kind of vapor barrier in the wall, but there is still plenty of gap around the roll up door that could let moisture in. Why no humidity there?

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What's the air temperature in the garage when it's 50 in the shop?

If the shop is 50ｰ and the dew point temperature is 41 the relative humidity will be 71 %. Let's say the dew point increased only 4 degrees to a temperature 45. The increases the RH to 82.8 %. This is what causes a concrete floor to become wet and these weather systems can change quickly. Your block walls may be moist and not be as visible as a concrete floor.

A few days ago all the windows in my garage were wet on the exterior and stayed that way for most of the day. I've only seen that happen twice in my lifetime. Eventually the glass temp. rose above dew point temp. or the air mass lost some moisture and the condensation dried.

 

[zmoz]

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What's the air temperature in the garage when it's 50 in the shop?

It stays slightly warmer in the garage, only because it's attached to the house. I'd say my garage usually stays about 50-55 with no heat and the shop stays close to 50 with electric heat. Both have finished drywall ceilings.

I don't really notice any moisture on the floor or the walls, just measured in the air. And a ton of surface rust on everything. The concrete walls are painted inside and out, if that makes any difference...

 

[JJT]

I have a shop built out of concrete blocks with a concrete floor. Ok, the seal around the door isn't 100% perfect, but why, oh WHY is it always so humid in my shop? It is often in the 70-80% range, about the same as outside. I use a dehumidifier in there but it just can't keep up with the amount of humidity coming in. There is only a little bit of insulation in my roof, and the temperature stays around 50 degrees. There are only two openings in the concrete blocks, one for the man door, one for the roll up door, and they're usually closed.

On the other hand, my garage, attached to my house, has no humidity problem at all. It stays below 50% almost always. The two buildings are very close, why the difference? My garage isn't insulated and the seal around that door is even worse than the one in my shop. I've never used or needed or even thought about a dehumidifier in there.

Is moisture seeping in through the blocks in my shop or something? It's really pissing me off seeing all my stuff get rusty. Really the only difference between my shop and my garage is that the garage is wood framed, the shop is concrete. The garage might have some kind of vapor barrier in the wall, but there is still plenty of gap around the roll up door that could let moisture in. Why no humidity there?

Seal the concrete floor. I used a clear concrete sealer sprayed on with a bug sprayer. That significantly reduced the moisture coming up through the concrete. Less than $100 to do 1200+ sq ft.

 

[zmoz]

Seal the concrete floor. I used a clear concrete sealer sprayed on with a bug sprayer. That significantly reduced the moisture coming up through the concrete. Less than $100 to do 1200+ sq ft.

Funny enough the shop floor is sealed, the garage isn't!

 

[Toyboy]

You didn't put a vapor barrier in the ceiling of shop...did you? Also earth floor drains will funnel moisture up into bldg. if you have any.

 

[jake98]

Also earth floor drains will funnel moisture up into bldg. if you have any.

Never would have thought of that! Floor drains as moist air ducts.. could happen under the right conditions I suppose.