Humidity Issue in Shop

[89MustangGX]

Hello,

Background:
Several years ago I bought property with a @20x30 shop. It's built as a pole structure. It has traditional siding, but no sheathing - only a tar paper type wrap underneath and studs inside are exposed. It is open all the way up to the roof inside. It is not well sealed - it is open between the trusses (bird block area) and the bottoms of the siding are not sealed well either - I can see daylight on some.

I had noticed a while back that my tools are getting a layer of rust on them, I checked and the humidity in there is very high. It seems to range from 70-85% on average!

I tried a 70 pint-per-day dehumidifier and it filled up with about a gallon of water a day but never really noticed the humidity change. It was in the 80's and went to 70's over the course of a few days, but not sure if that's weather related or from the dehumidifier -- in any event, I don't think it was significant change.

When I moved in, I had a new roof put on the house and shop at the same time. In anticipation of someday finishing the shop, I had roof vents added (8 box-type).

Questions:
Are the roof vents the cause of the excess humidity? Should they be blocked? I have cut a few pieces of 2x2 to help seal the areas at the bottoms of the walls and I can work on adding bird block - but I don't feel like that is the answer to everything. What can I do to reduce the humidity, short of sealing it up and adding HVAC? Do I just need a giant de-humidifier? Or is this all a symptom typical of a shop like this in the pacific northwest?

Thanks,

Adam

 

[Showkey]

It’s impossible to control humidity if the building is not insulated and sealed ( to a reasonable air exchange rate). It would be the same if your trying to heat or cool a structure with the window or door is open.

 

[Bretny]

Temp swings will allow things with any mass to have condensation on them..leading to rust. Unless you stop the temp swings you won't do anything.

 

[SGKent]

Super seal the garage then you could put an AC system in the garage with both the interior and exterior units in the garage. It would hold the overall temperature about the same and dry the air as much as you wanted. Or put the exterior unit in a side room with a roll up door on either side, where you could roll up the outside door to it in summer and vent the warm air into the atmosphere - thereby using it as an AC unit in summer, or vent to the inside in winter when you don't want the AC to make it colder. Don't call it a heat pump because if you dumped the cold dry air outside in winter like a heat pump does, you'd do nothing for humidity other than heat the garage. The goal would be to dry air without freezing yourself out. I think this would work if done right. Cooling in summer and dry air when you needed it. Building has to be sealed because every time the door is opened humid air is going to come in.

 

[Showkey]

Super seal the garage then you could put an AC system in the garage with both the interior and exterior units in the garage. It would hold the overall temperature about the same and dry the air as much as you wanted. Or put the exterior unit in a side room with a roll up door on either side, where you could roll up the outside door to it in summer and vent the warm air into the atmosphere - thereby using it as an AC unit in summer, or vent to the inside in winter when you don't want the AC to make it colder. Don't call it a heat pump because if you dumped the cold dry air outside in winter like a heat pump does, you'd do nothing for humidity other than heat the garage. The goal would be to dry air without freezing yourself out. I think this would work if done right. Cooling in summer and dry air when you needed it. Building has to be sealed because every time the door is opened humid air is going to come in.

Since relative humidity is relative to the temperature a little heat in the building can go a long way in humidity control:

 

[SGKent]

Since relative humidity is relative to the temperature a little heat in the building can go a long way in humidity control:

a little heat doesn't change the temp of the slab or cars although it would change the dew point. The issue is that all winter the slab and cars cool down. Then a warm front passes thru in the spring like about now, and the cold slab and cars pull water out of the air. On a 75 F degree humid day this time of the year who wants to turn on heat to drive temps up enough to change the dew point so water doesn't condense on the slab and cars (cold mass). This will continue until the slab and cars warm up. To stop it with a heater one would have to have an insulated slab, and keep the building warm all winter so the mass isn't cold in the spring when that warm front passes. An AC system is a giant dehumidifier.

 

[Showkey]

It’s not a little heat if the shop is heated. Consistent temperature control critical as the other posts mention.
If the garage/shop is heated the humidity can be controlled assuming sealed and insulated.

Let’s apply some Common sense ?...Obviously in warm climate adding heat is not an option.
Damp cold day or week Washington or Wisconsin heating makes a HUGE difference in the indoor humidity levels as the photo shows. It would not be practical to run the AC or dehumidifier at 50-60* indoor temps.......when the heat adds comfort.

 

[SGKent]

Showkey - if the exterior coil is designed to blow its air back into the inside there is no change in the inside temp. Humid warm spring day - 70F. The inside coil pulls water out and dumps it into the drain, and the outside unit puts the same heat back into the building. Lower humidity and no change in temp in this model. Want AC in summer? Roll down the inside door to the compressor-coil room and open the outside door. Now the warm air goes outside lowering the inside temp. One could accomplish the same with a room, and pair of interior and exterior fans/shutters. Adding dry heat to the building for winter would be nice too but the AC unit in this model is simply a huge dehumidifier to use in spring, early summer. Then in summer it cools because the air off the exterior coil is now being blown outside instead of back inside.

 

[89MustangGX]

Wow- I must have missed my reply notification. Thanks for the info guys. It really sounds like I have no options other than to eventually seal it up tight and control the climate. Appreciate the advice and good read.