Damp Garage

[krisway]

Background info first. I live on the east coast of Canada, province of Newfoundland. I have a 18x36 garage with concrete floor that I have been slowly finishing the interior with insulation, sheeted up walls and ceiling and adding heat.

Two years ago I had half of the garage insulated and sheeted up with 1/2" plywood. Garage was damp during the winter, usually being colder inside than outside. Opening the garage door allowed warm air to enter and thus make it damp.

Last year I completed the insulation, sheeted up the walls with 1/2 plywood and insulated the attic and used 7/16" OSB for the ceiling. Added soffit venting and roof vents as well. For heat, I have 5500 watts of electric base board heating. Last year for the winter months I kept the heat on in the garage all winter.

On the sheets of plywood that I installed two years ago, I'm noticing surface mould (dark specs). I'm wondering if this was due to the garage only being half insulated and NOT heated a couple of years ago. OR am I going to continue to see this mould grow. I'm wondering if I have something done wrong, not enough venting, etc. My worry is that the backside of these walls are mouldy too! I did use vapour barrier, is this correct or not?

I should also note that I drive a summer only vehicle and park it in this garage all summer. Some days the vehicle is parked in the garage wet. Which I guess is making the air damp?

So my biggest question is have I done something wrong? Should I have opening vents for the summer months? Should I invest in a de-humidifer.

 

[yeldogt]

A garage is no different than a house -- the more you can insulate and stop air movement the better you will be. If you live in a humid area at ground level you will most likely need some way to condition the air.

The air in the garage has nothing -- or should have nothing to do with the vents in the roof.

Sound like you need to get a dehumidifier and keep outside are from getting in when outside air is above 60% RH.

I have an Ultra Air unit in my garage .. they make a Santa Fe unit that is excellent. The better units really work and will keep the space bellow 50% RH all year and not kill you on electric.

 

[krisway]

A garage is no different than a house -- the more you can insulate and stop air movement the better you will be. If you live in a humid area at ground level you will most likely need some way to condition the air.

The air in the garage has nothing -- or should have nothing to do with the vents in the roof.

Sound like you need to get a dehumidifier and keep outside are from getting in when outside air is above 60% RH.

I have an Ultra Air unit in my garage .. they make a Santa Fe unit that is excellent. The better units really work and will keep the space bellow 50% RH all year and not kill you on electric.

Thanks, I'm thinking a dehumidifier is my next step. Maybe only needed on damp and humid days.

 

[yeldogt]

I open up my doors and windows on nice days ... otherwise I keep it sealed up. My dehumidifier is up on a shelf and controlled by an accurate humidastate.

What I have found is that if you get a good unit -- they are able to keep ahead of the problem. Once getting the space down to the proper RH .. they don't have to run very often if you watch the intrusion of moist air.

I'v tried using the smaller units with the removable tanks -- and they just don't work well enough for me .... they run all the time and never get the space dry enough. So you end up spending a lot on electricity.

 

[Andamo]

Get some sort of ceiling fan in there and keep the air moving and having a better ability to dry things up.

 

[kbs2244]

Humidity( “dampness”) goes from wet to dry.

Your first defense is local weather conditions.
If it is cool and dry outside, open the doors.

Your second defense is air circulation.
Even in damp conditions, moving air will not “cling.”

You will have to pay attention to local weather.
This is not a "set and forget" solution unless you want to get into all kinds of sensors and automatic controls.
And that is a hobby unto itself.

 

[toolmiser]

My parents (Wisconsin) had a humidity problem with the floor of their insulated 2 car garage. They found if they took out the attic door and put in a screen the problem went away. Might be worth a try.

 

[yeldogt]

If you floor is damp because moisture is coming up through the slab -- opening the shop up on dry days will lower the RH.

Ventilating any enclosed space with outside air above around 60% RH is going to be a problem.

 

[jgschroeder99]

Not sure what your budget is, but a heat recovery ventilator would probably work well. Not sure how big of a dehumidifier you would need for a garage with lots of air leaks (especially overhead door). An HRV would let you get rid of the moist air on dry days without losing heat in the winter.

 

[911mike]

Just get the air moving with fans. Try 2 box fans on the floor and a good dehumidifier. I ended up installing a high volume ceiling fan and keep it on low 24/7 and only need to use high a few times during the winter.

The damp floor most likely is from the cooler (lower) air condensation on the cold slab. Move the air and you won't have the cool layer sitting at floor level. The movement will help the dehumidifier too.