Low-tech dehumidifying?

Up here in eastern Canada, it is damp. It's usually quite humid here at all times of the year except during winter. I have a hygrometer it's rarely below 60% humidity inside, and there are parts of the basement that are starting to get a touch of a mold smell. (The basement in our new house is mostly unfinished except one room, and there is some mold on the drywall. I need to check if there are leaks behind it, otherwise the foundation is in good shape.)

But assuming a properly sealed foundation, how do you go about reducing humidity, if at all, throughout your house? Is there a cost-effective way to do it without relying on electricity to power a dehumidifier? Or is humidity simply something that you have to live with?

ClareBroommaker's picture

There's some discussion of basement dehumidifying here https://greenwizards.com/node/813

Do you know if your hygrometer really gives a good measure? I've seen crazy difference between different hygrometers in the same space. Although, if you've got mold, that seems like a pretty good indicator that the surface is pretty darned wet.

Thank you! Yes, I have a few hygrometers by different companies, two are digital, one of them is analog, and they all seem to give different readings. But 60% seems like it's reasonable.

Is there an ideal humidity that a room should have?

You've got to improve your air circulation.

Sadly, unless you've got a prevailing wind and operable windows on all sides, that's hard to do without electricity.

Some suggestions to improve air flow:
ALL your shelving should be Closetmaid. That is, it should be vinyl coated wire shelving. This is easiest to do in closets and pantries. Closetmaid shelving is adjustable with a hacksaw.

Use vented louvered doors wherever you can. They don't work for bedrooms but for closets and pantries, they're great. We've also got a louvered door to the upstairs bathroom. Because of the way our house is built, that bathroom is only used by the person living in our bonus room attached to the bathroom. It might not work as well on a main bathroom, but if you need more air flow, you should think about it.

Bathrooms need venting, both a window and a ceiling vent.

Open windows all around, from top to bottom.
Make sure your attic is fully ventilated with ridge vents and soffit vents.
Basements need venting too, as do crawl spaces.

Yes, extensive venting can wreak havoc with heating and cooling so you want to consider if your vents need to be operable.

Sunshine can be helpful so more sun reaching deep into your interiors won't hurt either.

We're working on getting those vents in the attic, which should help. And thankfully the basement has windows, lots of them. It's partially finished, and I did find at least one leak. I'm thinking of unfinishing it to check for further leaks, but then that would involve taking out the insulation. So maybe I will have to do some serious work to the basement, and then live with a dehumidifer.

Some of the insulation in the basement, and in the attic, is normally pink-colored, but now has some black substance covering parts of it. Probably also mold...

lathechuck's picture

My electric dehumidifier can pull a gallon or more of water out of my basement in 24 hours, day after day. It's noisy and expensive, though it's the kind of job that would be fine running on intermittent (e.g., solar panel) power, because it wouldn't matter if it only ran during sunny hours, and missed a day or two. There are chemicals that absorb moisture, but these are only practical in sealed containers. If someone says that a bag of chemicals can dry your closet, or basement, ask yourself "where does the water go?" and "How do I tell if it's still working?"

I've used and still use both.

DampRid works in small locations, like a closet. You MUST have the bucket within a bucket setup whereby the DampRid crystals sit in the upper, perforated bucket and the water drips down into the bottom bucket. The buckets that DampRid come in at the grocery store are small; about 2 pint size. To successfully use DampRid, you must check the bucket at least every other day and dump it. You've got to add extra crystals (bought in gallon bags at Lowes) regularly to continue absorbing water. DampRid will let you control moisture in a small area but that's about all it will do.

For a large area, you'll need a dehumidifier. As with so many other areas of maintenance, the more water you can keep outside where it belongs, the less hard your dehumidifier needs to work. Dehumidifiers will not hold back the tide.

In our experience, our basement had all kinds of water issues. We took care of (a decade-long process) water infiltrating from outside. That helped more than anything. When we first bought the dehumidifier, it ran continuously, only stopping when the bucket filled up.

Eventually, a process that took over a decade, the dehumidifier stopped running on its own before the bucket filled up. That is, when the sensor says (and I use the lowest setting) it's time to stop, the dehumidifier stops. I think it's about 40%? IIRC?

What happened is that first, we stopped the water infiltration. Second, we improved overall ventilation. Third, over time, we gradually removed all the water that had been absorbed in the joists and walls. There isn't as much moisture in the air and the building itself as there used to be. Thus, I don't need the dehumidifier roaring away continuously.

It took over a decade. Again, you have to fix your water infiltration issues FIRST or you're just bailing.

Both DampRid and dehumidifiers produce water but you'll need to handle the water differently.

I ALWAYS toss DampRid water down the toilet. I don't know what's in it after passing through those magic crystals.

Water from the dehumidifier goes on plants, either indoor or outside. It's just water. I suppose you could drink it, if you had to.

Just like distilled I would guess.

ClareBroommaker's picture

If we are talking about something bigger than a polyacrylate packet with which your shoes or vitamin tabs come packed, then the water goes to what ever collection vessel you (or the manufacturer if using something like Damp-Rid that Teresa mentions) provide.

In the older thread I linked above, what I had in mind was to pour Calcium chloride (same as Damp-Rid) into a plastic tub or glass vessel. The more surface area, the better. Vapor sticks to the crystals until the crystals dissolve in the water that sticks to them. In the commercial system, water drips off the crystals into a collection bucket. My idea was to simply save the resultant fluid right in the tub or glass vessel and dry it out for re-use by driving the water away under the heat of our solar oven.

When I was a child, my parents had a cookie tin which had a humidity absorber in the lid. When an indicator in the crystals turned lavender-pink, it was time to put it in an oven to dry out the crystals for re-use. Likewise, I had a ceramic toy dog that was coated in probably the same Calcium salt with indicator. When the dog turned lavender-pink, it was supposed to be an indication that rain might be on its way. These very small amounts of calcium chloride could be used repeatedly. Given time and heat, it seems to me the calcium chloride in a nonreactive tub could be used again and again.

I have not actually tried this yet. I'm sure it is a lot of fuss compared to using an electric dehumidifier.

I have no doubt that an electric dehumidifier can remove water from the air much more quickly. Does your dehumidifier put out a lot of heat?

Yes, ours did. It didn't feel like that much, but then we ran our dehumidifier ONLY in our unfinished basement.
That space is always cold, even in during August, so the heat wasn't a problem.

I would NOT want to run the dehumidifier in living spaces during August.
Like incandescent lightbulbs, you get more heat than you expect.
Sometimes that's useful (in winter), sometimes not.

Ah, those are good points. Thanks for the warning!

Sweet Tatorman's picture

If those solutions are not viable for you, I am in agreement with Lathechuck and Teresa up thread with the exception that I cannot quite get my mind around Teresa's comment regarding louvered doors and bedrooms.

David Trammel's picture

If I had to guess, Teresa probably means to cut down on mold and moisture in small areas, to promote airflow.

I'm doing something of the same sort with the two closets in the basement, putting louvered doors on them. I also put a one inch air gap between the foam insulation glued to the walls and the metal frame walls which are covered in cement board and dry wall.

Moisture gets you when there is a temperature difference between the air and a surface. Cooler surfaces tend to attract condensation, and then mold growth. The more you can equalize temperatures the better.

Louvered doors allow air to circulate all on its own. Not well, not like a fan or a breeze would, but if air is moving around inside your house, the louvered door will let air go and out of that closed space. If you leave the door open or remove it entirely, you won't need the louvered door. However, some spaces need closed doors.

Because a louvered door is made of open, stacked slats, you'll also get light leakage and sound carries right through them. Your privacy levels will vary: can you tolerate a louvered door on your bathroom? You'll get sound and moisture but you can't peek through them.
A bedroom can be more challenging: privacy in terms of sound AND light leakage if you need a darkened room to sleep in and the rest of the house is lit up. This is really important for shift workers.

I just checked the currant humidity level for Salt Lake and it is at 17%, dew point is 45 degrees and we won't be getting that naturally for some months yet. Not that mold can't grow here with AC and bathrooms that aren't vented.

Ha, as time goes on and it gets hotter here in the summer, it could be that Nevada, Utah, New Mexico and Arizona weather may be coming to me! :)

David Trammel's picture

Humidity and the problems of mold are a important issue for me, since I'm moving into the basement of the new place. I've not researched it as well as I should yet.

I'm focused more on initial issues of prevention of water entering the basement, and not yet lowering the humidity of the air in the basement. To do this, I first went around and patched all of the cracks I had in the cinder block walls. And I had quite a few too.

This involves chipping the cracks out until I had a 1/4" gap all the way thru the first wall of the brick and patching the crack with hydraulic cement. Working with it was actually pretty easy, like playing with PlayDow. I also gave the boundary between the wall and the floor a coat too. Here's a picture.

Next I covered all of the exterior walls with a 1" layer of polyiso foam board. Its the silver foil faced stuff with a vapor barrier on one side. It and the metal wall framing I'm putting in sit on a EPS foam subfloor. This is so that if I do get any leaks later, the water should (in theory) move to the bottom and then head towards the drain. The floor has a slight slope.

You can see the foil faced panels in this photo, as well as the subfloor. The pink panel under the grey kitchen cabinet.

After I get all the walls up then I'm going to be insulating the rim joists, which are the areas just above the basement wall and below the first floor floor, in between the basement ceiling rafter beams. And caulking all the windows for air gaps. I'll probably replace the old exterior door too eventually.

All of this is the cut any infiltration of exterior air as well as to provide a boundary layer between the cooler exterior walls and the floor and the warmer moist interior air. That's where you get much of your damage. Warm moist air hits cooler surfaces and the water gets deposited there, providing a place for mold to grow.

Common drywall has a big problem with that. It likes to retain moisture. I'm actually using cement board, which is pretty much moisture proof on the first 3 feet or so of wall, then moisture resistant drywall above that.

For comfort I'm still probably going with an electric dehumidifier, though the main living area, an office and a bedroom, will have a door to segregate them from the rest of the basement, as well as an additional 2" layer of foam insulation in both the walls and the ceiling.

Thanks for this! That makes a lot of sense, especially the point about drywall soaking up moisture that arises from the cooler exterior walls interacting with the moist air inside. We have drywall along some of the walls in the basement, which I actually may take down. Do you also plug leaks by digging around outside to find the source of the leak on the outside part of the basement wall?

David Trammel's picture

I actually have no water leaks in all but one crack. And that only happened in the huge storm we had last weekend. But I could see thru the wall cracks and I wanted them sealed before I glued the insulation on. Once its up, there's no taking it down.

We have about 4 feet of the cinder block walls which are above the ground. Useful for big windows and if I have to exit through them, means I don't have to try and get out a well. Bad because there are several minor cracks in the walls outside where the foundation and wall have settles. The cracks develop in the mortar between the bricks.

I may go back and see where I can patch outside but its not a priority. The reason is that from my reading, sealing the exterior with the interior having a vapor barrier on it, may cause the space within the wall to fill with water. Concrete will breath and allow moisture to pass thru it and out. Water that goes into the space in the bricks I believe drains out the base. So I want ground water and rain to evaporate outward.

The vapor barrier isn't 100% water proof. It just slows the passage of moisture to the point that there's really not enough to condense on the wall. To help take care of any minor moisture I actually have a 1" air gap between the insulation and the backside of the wall frames. The top of the gap is open into the rim joists behind the insulation in the walls, and should allow moisture to exit into the outside.

lathechuck's picture

In cold climates, you need a vapor barrier between the warm, humid indoor environment and insulation, so that the vapor barrier stays warm enough not to cause condensation (or freezing!) which would soak into the insulation. But in hot, humid climates, the vapor barrier has to be outside the insulation, so that condensation from the cold (air-conditioned) interior doesn't soak into the insulation. In my mid-Maryland temperate climate, the biggest energy expense is heating, so I assume that the vapor barrier (if there is one) is inside.

That's one MORE reason not to run the A/C down too far (in addition to household expense, and global environmental impact). We've got it set to 78F, and run a dehumidifier all summer. Sometimes, we'll knock it back to 76F for cooler sleeping (under a slow ceiling fan).

Given that we can trade-off temperature and humidity for equal comfort, I think it's best to go for warm and dry! Heat conduction (which the A/C counteracts) is proportional to the temperature difference, not the humidity difference.

David Trammel's picture

In several places I can look into the air gap and check for moisture but I'm not using any fiber type insulation matting. Everything is foam board so it shouldn't absorb any moisture. The dry wall is all the type that is treated to resist moisture.

I may run some temperature experiments this Winter by hanging a thermometer down into the space, then another in the living area, perhaps even one into the spaces inside the concrete blocks themselves and of course one outside. Then take time based readings and see how the temperature varies across the layers of insulation.