earth bermed garage got moldy

Hi.
I bought a house this spring on an east northeast facing hillside in Virginia. I know south is better, but $$ and commute and privacy were big factors. Anyway, the garage is tucked under the house, so that the doors and one wall are exposed, and they are not insulated. The back wall and ceiling are part of the house, and the south wall is underground concrete block. The south wall stays nice and cool, and I thought this would be great coolness for working out there in the summer. But what happens is that every time the doors open, moist air comes in and condenses on that wall. So we got a dehumidifier, and run it 24/7 and there is a constant trickle of water out of it. The frogs are happy, the mosquitoes are happy, but I need to reclaim a workspace. By the way, you are more likely to find a yeti colony than an actual car in our garage. There are reports of a glass kiln and several sheep fleeces, an air compressor, and a stained glass workshop in boxes out there. And an HP server with a thousand CDs of music.

A) I could live with it through the winter to see what else happens.
B) I could insulate the cold wall, and lose the a/c. Try to make the dewpoint inside a solid.
C) Can I insulate the door and exterior wall, to try to keep the room cooler? Maybe a curtain would limit the air exchange?
D) can I turn the cold wall into a dehumidifier, trap the condensate and expel it?
E) I could admit the dehumidifier is required, and look for a solar DC model?

I'm open to unconventional ideas, or else I wouldn't be here, but I'm new to this, so reference links and definitions are welcome. Efficiently controlling humidity is going to be key to using this property.
Humidity is at once the water of life and the evil destroyer of material goods. How can I dry out my garage?

Thanks for your input.
Lyvia

Could it be the wet weather? I've been in my house 4 years and the crawl space/storage room has never been this damp and in need of a good drying out. If you have been having unusually heavy rains, like we have had further south, maybe just borrow a dehumidifier for a while and see if it returns to "normal" in the fall.

I guess I am suggesting a mix of option A and option E.

Its a tough situation and very similar to the issues I face in my own basement. Thats great you dont park your car in there.. dont. Being tucked under your house, the air in there is probably the same as the air in your house. Iam betting that its contributing to your AC load in the summer and will make your house harder to heat in the winter.

If your were going to build such a structure new (not that I would recommend an attached garage) You would put insulation to the exterior of the walls with redundant water proofing and dampproofing techniques. The best way to fix the issue would be to excavate and install such measures. However, thats also the most expensive way and would avoid it by trying other stuff first.

First of all, keep your gutters clean and carefully evaluate your finish grade on the uphill side. You want water to flow away from that back wall (and area around it) as quickly as possible. The more water that soaks in back there, the more humidity your basement/garage/house will experience. I would consider a french drain (gravel with hard pipe to daylight and silt fabric burrito) if it would be difficult to change the grade which it often is.

Second of all, get very vigorous with your air sealing. I would consider building a wall in place of the door. The doors are probably leaking lots of humid air into this space even when they arent open. The mudsill is also very likely a source for air leakage. Look around down there during the day time with the lights off. If you see light, seal it up!

Dont stop with the air sealing in the basement. Air generally flows out through the roof and ceiling so if you block the air movement there, there will be less coming in the cracks you cant find or get to down lower. Get up in your attic, peel back the insulation around any lights, wall top plates, soffits and pipe penetrations and go to town with some canned foam. Always do this before adding insulation...

Air sealing the ceiling plane to stop mold in the basement? Absolutely! Your dehumidifier will not run as much as it handles the small volume of air in your trouble area as opposed to constantly dealing with the outside air flowing through your house. This will also decrease your heating costs.

Insulating the interior basement walls can be tricky and the payback is questionable but I would consider it depending on the details of your situation. After all, mold is unacceptable and constantly running a dehumidifier is bad for your monthly energy costs and the environment.

Thanks - you are right. I was focused on heat transfer and forgot about sealing air flow cracks.

While I don't have any experience with your problem I would try D).

The earth berm is naturally going to be a cold sink and likely below the dew point for your humid environment. Thus rather than trying to fight it I would use it. After sealing all the air leaks to the garage can you also seal the concrete with a hydrophobic material/spray? My thought is to trying and prevent the water from absorbing into the concrete and keep it on the cold hydrophobic surface. My next thought is to then take stainless steel wire attach it to the wall and create what would look like a river network on the wall that will allow the water to run downhill on the wires and into one collection point. If the amount of water is great enough you can put in a sump pump to pump it outside or if small enough taking the bucket outside every couple of days.

My idea is a little "pie in the sky", please critically evaluate.

Best of luck

Interesting, a homemade all-natural dehumidifier. Iam thinking there would be a bigger moisture load on the exterior side especially after air sealing the volume of air around the interior side. Might create more problems if the masonry cant dry to the interior like quicker rotting mudsills or worse, hydrostatic pressure.

There is good evidence that closed cell sprayfoam can be a good fit for these situations especially old and difficult to detail rubble walls. The tricky part is needing to create similar channels to daylight below the foam. This would be another expensive but possibly cheaper route than excavating the exterior side for retrofit.

Truthfully, without these expensive and invasive procedures, old and poorly built spaces below grade may always need a dehumidifier. Its a shame too because they use a lot of energy. Its tough to make passive technology that matches the effectiveness of phase change refrigerants and fan-driven moving air.

Brett, thanks - that crystallizes what I have been thinking. The problem is uncontrolled condensate, so instead of pre-empting the condensation, just control the condensate.

We do have hydrostatic pressure on that wall, and it has carbon fiber strips. We could seal around the strips, but I have to think that through. (Sounds reasonable, but those words can precede home disasters.)

We might excavate at least some anyway. DH wants to try it with the tractor. Since we have only had the tractor for a month (NEWBIE!), I'm hesitant to use it that close to the house. I'm thinking regrading might help. I'd really like to build at least a porch out there, and keep all rainwater well away.

Such a project.

Has anybody tried controlling condensate like that? Maybe in a greenhouse?

Good point Brian,

I didn't think about the exterior moisture entereing the masonry. Yeah, if the masonry can't breath and there is lots of moisture is in it will definitely degrade quickly. It wouldn't be a problem in the high desert where I am located as the ground is pretty dry. Yet, east of the Mississippi, maybe not so good an idea to seal the masonry. Don't seal the concrete.

Yet, I wonder if the cold stainless steel wires could still act as a passive dehumidifier if attached to the concrete.

Sealing the concrete may not be so bad as long as there was a way to prevent the build up of water (hydrostatic pressure) through the use of drainage channels to a sump pit or daylight. Thats the hard part I think.

I guess stainless steel would be a good choice for something like that because its cold and wont degrade fast. Problem is (besides considerable expense), it wont get cold enough on its own to attract and drain a meaningful amount of moisture.

I know hubby really wants to use that tractor but excavating an entire basement wall is tricky business. Be careful. You should definitly be trying to fix the grade on the uphill side of the house. Ever see how highways use lips at the top of a cut area to direct water away from it? If the cut is big enough they terrace it so there is not too much water ever running down the hill. If you have much hill above you grade it like the DOT does. Ideally, the first ten feet of grade around the house should be sloping away from the house. That should then slope as much as possible to prevent water from penetrating the ground or pooling up. Clay and other impervious dirts are helpful in these situations.

Didnt want to imply bad advice there. Was thinking some houses will never be alright with just good surface drainage. I suppose waiting out this wet period is really good advice but some homes have such high ground water that they will need major retrofit. Especially with a few more years of this type of weather on the east coast.

Thanks for the clarification. I did back peddle my original idea because the last thing I would want to do is cause damage to the house.

Directing the water away from the house also sounds good too. What do you think about compacting the Earth/dirt on the exterior side of garage and removing any vegetation? (I don't like to remove vegetation personally) I am just think about getting the dirt on the outside of the wall really compacted so it is less permeable to water. Any rain or moisture will have a hard time penetrating the ground and thus less moisture to the garage wall.

Hmm. So far I made a "free inspection" appointment with a basement waterproofing company, then got sick and cancelled it. So still open to ideas.

How would I attach a channel like a wire to the wall? Duct tape? Or maybe fashion a condensate channel out of duct tape?

In the Air Force I used to hem my blue uniform pants with duct tape. And mend my socks. It goes through the washer better than you would think. But it would not attach to a damp surface.

I re-evaluated the drainage and dug a tiny trench by hand before I got sick. There is definitely an avenue to improvement there. There is also a crack to be caulked. DH won't caulk it because he says he has to excavate first. So any air leak just keeps going. And of course the caulk and supplies are in the moldy garage. So frustrating!

I have a lot of condensation on cooler walls, and use candles or lamps to keep the wall surface just warm enough to halt the condensation. If I had electricity, I would use light bulbs or some computer fans. It might be a good temporary solution and less expensive than running a dehumidifier while you ponder the big plans. Good luck with it!

Part of the problem is that the outside wall is connected to damp fill that is a good heat conductor, always making it earth temp and close to dewpoint.
How about burying some plastic sheet from the wall out 20' or so to keep the soil against the wall dry. It's temperature will be closer to the inside house temperature and above the dewpoint. Dry fill will hold heat transferred from the concrete and become a massive heat sink, moist fill will wick it away quickly.
Actually 3 layers of plastic sheet with 1" of styrofoam between the layers.
The author's name escapes me but the book is Passive Annual Heat Storage, explains the whole thing in detail with a different objective but I think it would solve your problem.