Humidity: What's the maximum amount?

[AdamIsAdam]

I was wondering what people think is an acceptable level of humidity to have in a garage?

I recently started renting a 2 car garage that is built into a hill, so it's about half below grade. As such, the humidity can be as high as 90% if left closed up so far this summer. I don't know what it will be in the winter. My restored 1964 Pontiac is not there yet, so I'm just testing things.

If I run a dehumidifier that does the trick and can easily bring it to 60% or less which seems fine, but the electric is about $75 a month just for that!

I painted the 3 walls and ceiling (all concrete, since there's a second story garage above me) with Dry-loc cement paint and that seems to have helped quite a bit too. I also just put in two 4lb buckets of DampRid FG50T Hi-Capacity Moisture Absorber, 4-Pound Tub https://www.amazon.com/gp/offer-list...&condition=all

I'm also running fans because that helps the dehumidifier, plus circulation and fresh air helps with humidity in basements/garages. I may add vents to the garage doors (with screens) to let fresh air in and humidity out.

I know winter will bring lower humidity here in NY, but I'm worried about parking the car in this place all winter. Should I be? What can happen to the car? Do I need to run the dehumidifier?

 

[Showkey]

Depends on temperature and how well the building is sealed but 50% is an acceptable goal and after 70-75% bad things start to occur like mold and mildew on organic material like leather, paper and some rubber products. Higher than 75% surface rust on untreated metal willl occur quickly.

Once you run a dehumidifier do not run fans or exchange the air from the outside that just defeats the purpose of running the dehumidifier. Keep the building sealed as best as possible and practical. Yes on dry 40% outside humidity ventilation is ok but not needed or really effective in the long run. Once you “condition” the air keep it conditioned.

 

[AdamIsAdam]

Hmm. There's no HVAC in the garage. 3 walls are cinder blocks with extra concrete outside that was added when they built the second garage on top, along with cement ceiling and steel I beams. So aside from garage doors the garage is basically closed up. The seals on the garage doors are old and very worn.

That being said, in the summer it was more humid inside the closed garage than it was outside. It's about 90% humidity inside on a 70% outside humidity day.

Hopefully, winter will bring lower levels. The garage has been empty all summer. I'm nervous to bring my car there, which is bad since I'm paying a lot of money for rent!

So if 50% is my goal, I want to see if I can accomplish that with just fans and the DampRid products which are much cheaper than electricity.

 

[200.447]

Is the floor sealed?
Most of the humidity comes up through the floor. Concrete is porous!

When I built my garage, I laid 4 mil plastic on the sand before the floor was poured. Worked wonders. Have cut metal pieces over a decade in there without any rust on it...

So, look into sealing the floor asap.

 

[AdamIsAdam]

I don't want to go through the expense of sealing the floor since it's a rental. I was thinking about buying some sort of vinyl floor covering since I can take it with me, like this: http://www.northerntool.com/shop/tools/product_200361265_200361265

What do you think?

AND is it still somewhat effective to cover most of the floor area (like an area rug) as opposed to covering 100% of the floor? Will that reduce my vapor coming up from the floor?

 

[finn]

Relative humidity is higher inside than outside in the summer because the indoor temperature is lower than the outside temperature.

A dehumidifier will do the job, and insulation on the cement walls may help a little to keep the cool walls from sweating.

 

[ishiboo]

Hmm. There's no HVAC in the garage. 3 walls are cinder blocks with extra concrete outside that was added when they built the second garage on top, along with cement ceiling and steel I beams. So aside from garage doors the garage is basically closed up. The seals on the garage doors are old and very worn.

That being said, in the summer it was more humid inside the closed garage than it was outside. It's about 90% humidity inside on a 70% outside humidity day.

Hopefully, winter will bring lower levels. The garage has been empty all summer. I'm nervous to bring my car there, which is bad since I'm paying a lot of money for rent!

So if 50% is my goal, I want to see if I can accomplish that with just fans and the DampRid products which are much cheaper than electricity.

DampRid is not going to do the job... you need a dehumidifier until you hit winter. The temperature swings are what really causes condensation to form though. Controlling where humidity is getting in is a big part of it.

Just like air conditioners, going with an energy-efficient "central" unit vs a window unit is much cheaper to operate, but they are of course much more expensive to buy... the Aprilaire standalone is like $1100.

 

[AdamIsAdam]

...Controlling where humidity is getting in is a big part of it...

ok, then is it still somewhat effective to cover most of the floor area with a roll down vinyl flooring as opposed to covering 100% of the floor? Will that reduce my vapor coming up from the floor? The roll down flooring is at least portable (remember, this is a rental), but it's not cheap! So if I cover 80% of it, will that get me ~ 80% reduction in moisture coming in from the floor or am I better off spending that money on electric bills?


Hopefully the winter won't be an issue then. I HOPE!

As for summer, if I need to run the dehumidifier, I guess it's a cost of storage.

 

[AdamIsAdam]

Just fyi, I've had the dehumidifier running along with two big fans and 2 buckets of DampRid in the garage for about 36 hours. Current weather is 72*F and raining, dew point is 72* and humidity is 98%. Inside, it is 68*F and 54% humidity. Felt nice in there.

It's looking like I'm going to have to run that dehumidifier all the time, aren't I? At least when my car in parked there. :-(

 

[trashmanssd]

yes there is no substitute for running a dehumidifier. I run 2 in my basement and I run one in my detached garage (detached also has a heat pump system for heat and A/C but that only runs a few months to stave off extreme temps), my attached garage doesnt get nearly as bad as it shares 2 walls with the house and the house has central air, also I leave the door open to the house a few hours in the afternoon early evening to warm it up in winter or cool it in the summer.

 

[toyotadriver]

Lack of insulation on those concrete walls means they are cool and likely condensing moisture. The moisture then evaporates and starts the whole process over again.

Part of the issue likely is the building is closed up and so the concrete is staying too cool. You need to warm that concrete up. Leaving doors open on nice days to help warm up the concrete will help.

Regardless, you'll need a dehumidifier.

 

[AdamIsAdam]

ok, let's talk insulation then. Remember, this is a free-standing, remote building that is not on my property. So garage doors are closed 99% of the time. And also remember it's a rental.

That being said, do I need insulation or more of a vapor barrier on the walls? What type of insulation?

I did paint the entire place with 2 coats of DriLok paint that seems to have really improved the condition, believe it or not. (The day I first saw it there was condensation on the wall cabinets and dripping off the I-beams. I almost didn't take the place. There was leaking water on the corner that has stopped since the DriLok. Also, the brick steps outside that run the entire side of the building are crumbling and the owner plans to rebuild the entire thing with poured concrete, so I'm hoping that pitching that away properly will help things too.

 

[Bretny]

Hello from a few hours north. You may need to run the dehumidifier up until things start to cool down, about late nov. U should be good until the spring thaw.
I have a dehumidifier in my basement and it was costing me about $75 a month to run and not gaining much head way. Got turned off 5 years ago. Your problem is prob water migration through the concrete like me. I own the house and prob will never fix it. Requires me to rip up the whole basement floor.

 

[rsanter]

Paint the floor. I know you said it’s a rental but basic garage floor paint is not that expensive.
Perhaps the owner will pay for the paint of you apply it. Explain that there is excessive humidity and that can cause mold and other issues to the structure

Bob

 

[AdamIsAdam]

Paint the floor. I know you said it’s a rental but basic garage floor paint is not that expensive.
Perhaps the owner will pay for the paint of you apply it. Explain that there is excessive humidity and that can cause mold and other issues to the structure

Bob

Yea, that was my original plan, to paint the floor. And I've done it once before. But the floor has a fair amount of oil stains on it already and I just ran out of steam in my plan to do that. Plus I read that if the floor has excessive moisture coming up that the floor paint will not stop that, the moisture will push up and cause the paint to peel.

Which brings me back to a roll up vinyl covering. Fast, easy, and portable. They're not cheap (they vary, and most stores on line are sold out right now for some reason), but I can have it for life and move it to my next garage should the need arise.

I would think if I cover 80% of the floor, I'd cut down on humidity seeping up by 80%. Especially good for the car which will be parked on top of the mats and covered. No?

 

[justinjoyal]

Relative humidity is higher inside than outside in the summer because the indoor temperature is lower than the outside temperature.

Exactly what I was going to post.

People often get fooled by %RH.

Remember warmer air holds more water.

 

[AdamIsAdam]

Just thought I'd post an update. I decided to put down a pit mat on one side of the garage. I figure it'll reduce moisture coming up directly under the car, and it looks cool. Plus, naturally I can take it with me if I leave or use it at car shows.

The humidity stays about 50% now that it's cooler. The landlord rebuilt the steps that run along the outside of the garage with the grade and found that the drain pipe for gutters wasn't connected under ground, so hopefully both the new steps and plucking will help reduce moisture around the outside of the building. If not, I'll run the dehumidifier on the summer.

Here's the garage with new lights installed, quick Jack, and my tools.

Next up, heat!

 

[dadsEH]

Yea, that was my original plan, to paint the floor. And I've done it once before. But the floor has a fair amount of oil stains on it already and I just ran out of steam in my plan to do that. Plus I read that if the floor has excessive moisture coming up that the floor paint will not stop that, the moisture will push up and cause the paint to peel.

Which brings me back to a roll up vinyl covering. Fast, easy, and portable. They're not cheap (they vary, and most stores on line are sold out right now for some reason), but I can have it for life and move it to my next garage should the need arise.

I would think if I cover 80% of the floor, I'd cut down on humidity seeping up by 80%. Especially good for the car which will be parked on top of the mats and covered. No?

Go to a carpet store an ask the guys to save you some carpet they have replaced. It will probably only cost you a slab of beer. They have to dispose of it anyway.

Carpet will keep your chassis dry underneath.

 

[AdamIsAdam]

Go to a carpet store an ask the guys to save you some carpet they have replaced. It will probably only cost you a slab of beer. They have to dispose of it anyway.

Carpet will keep your chassis dry underneath.

Interesting idea

 

[Ak Jim]

Another possibility is one of the car storage bags from a place like California Car Cover. Maybe nor super convenient but it would keep the moisture out.

 

[AdamIsAdam]

Another possibility is one of the car storage bags from a place like California Car Cover. Maybe nor super convenient but it would keep the moisture out.

Yea, I thought about those, but I want the entire garage and contents to be at a reasonable level and protected from the wrath of humidity.

I plan on running the dehumidifier over the summer. In the winter so far it's between 45-55% and spiked as high as 66% during rain. All acceptable.

 

[larry4406]

....It will probably only cost you a slab of beer.

What is this “slab of beer” measurement? New one for me.