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wofati and earth berm

Wofati demo site in New England—humidity mold questions

Joshua Myrvaagnes

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posted 1 year ago

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Near a river.

Deep well shafts like the greenhouse at the lab??

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Mike Haasl

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Could you elaborate on your question a bit?

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Joshua Myrvaagnes

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Sure, I was rushed before.

Here's the context--
I want to have a wofati exist on the East Coast, near-ish to Boston and NYC that people can travel to it without having to fly a plane and get to Montana from here. I have the perfect space for it, with slope in this one spot, and there are lots of trees that the highway dept took down. (unfortunately a little big for me to carry by hand solo, but we'll get back to that).

This year we had a lot of rain, and we live near the river. We had mold in the basement. We had mold on the first floor. whenever I’ve asked somebody about the wofati idea in New England, they said that water would come up out of the ground and be a problem. I don’t think they understood, the design very well, but that’s what they said. But I am thinking that there needs to be some accommodation for the huge amount of humidity. My sense is Montana is much much much drier. We usually get a lot more rain, about 40 inches.

Would making deep wells like the ones in the wofati greenhouse draw the moisture down and condense it there? Will the condensation happen low enough that the mold isn’t sending gases or whatever toxic things it has in it up into the breathing environment ?the wofati temperature should always be that room temperature, and the below ground about 55 . thoughts?

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Mike Haasl

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Much better, thanks!

I have similar concerns about a wofati in a midwest or coastal location. I worry that the ground will wick water up from below and rot the posts out. I hadn't thought of mold but that's probably related.

I'm not sure what causes mold to form but I'm assuming it's a combination of high humidity levels and stagnant air. I honestly don't know how a person could keep the humidity in a wofati below 50% in Massachusetts. The ground naturally would be a very high humidity. The umbrella will help and maybe it would keep the majority of the water away. I'm not sure about ground water wicking up from below, especially depending on how high above that river you are (and likely the depth of the local ground water).

Even with all that, I have condensation on my windows in the fall and winter in a normalish house (wood heat). Drying out the air in a house in the fall is hard if you don't have forced air or dehumidifiers running.

All of this doesn't answer your question about the wells. I'm guessing, but if the well provided an extra cold spot (pipe sticking up) for the humidity to condense upon, and it ran down to a place where it stayed out of the structure, maybe it would be a natural dehumidifier?...

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Timothy Norton

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I don't have much experience to be able to give an answer but this thread had some ideas/source worth looking into.

https://permies.com/t/62494/Passive-dehumidification-control-mold-grid

Hope this might help get something brewing!

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Aaron Yarbrough

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For the subfloor I think I would put in 4-6 inches of gravel, 6 mil poly, insulation panels and then 2 inches of gravel. I would also insulate the bermed walls from below the subfloor up. This would moderate the temperature within the building envelope so you don't have 55° F coolth creeping in from the ground meeting the warm interior air and creating condensation on your floor and lower walls. Wood heat should keep interior humidity low in the in winter. You might still need some mechanical dehumidification in the summer.

We live in a pretty humid place and have a partially earth sheltered cottage and I ended up installing a mini-split primarily for dehumidification.

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S Bengi

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I would tackle the high humidity the same way I would in any house.
Vent bathrooms/steamy shower
Vent stoves
Vent furnaces
Vent clothes dryers
Use a ERV to bring in and buffer incoming air makeup
Earth sheltered wofati are wrapped in plastic on all 6 sides, so there shouldn't be a crazy amount of infiltration
And lastly use a dehumidifier to reduce humidity if needed.
Another potential humidity source is leaks in the plumbing system, esp with the hard freezes that can burst pipes every few years here in New England. PEX piping seems like it would be the best option.

If needed I would also use a whole house air filtration system to tackle smells, MOLD spores, viruses, bacteria, etc

There are also condensation issues at the interface of the warm indoor environment and the cool outdoor environment. Having enough insulations at room temperature will help this.

But to answer your question more directly. I don't think that the "earth tube/well shaft" would provide enough "natural dehumidification" to be effective in our humid air and saturated soil environment. I think that a "cold window" would be more effective because the glass is inert and wouldn't grow mold and the window(s) could easily be below the dew point and thus allow condensation to happen. The windows would naturally be colder in the winter and during the summer, is you could get the river/spring water to gravity flow to the window and then "chill it" it would also enable condensation. The question now becomes where would you send all this condensate. I propose that we look towards regular mini-split AC and dehumidifiers for inspirations.

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Joshua Myrvaagnes

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Thanks for the replies.

Today I learned humid air is lighter than dry air. (

?) Avogadro's law, the same number of molecules sit in the same volume of air, larger molecules will fit fewer molecules in, and so there's less mass. Sometimes I think nature is trying to mess with our heads.

Anyway, the sink tube would need a cold pipe that goes way up to the ceiling.

A saving grace of the wofati in summer: it will be warmer than the average temperature of nighttimes. Nothing will condense at night.

Daytime, it is a cooler spot than ambient air, and it will condense moisture on it. I suppose it will be OK if the condenser IS the house--if all of it is cobbed over, if the cob is angled (not horizontal) so that there is a direction for consensate to flow.

Cob stalactites on the ceiling? (Kinda ruins the log cabin look, more cave vibes here, but better that than mold chic.)

How dry is Montana really? is this an issue sometimes there? I'm going to look at the Lab passive greenhouse threads to see if there's anything on it there.

As for venting in the bathroom, our mold did not appear in the bathroom. It was on leather bags in a room far away from the bathroom, and on furniture in that room. It had an air conditioner going some of the time in there (except on rainy days when it was cool), it has no plumbing, it is on the northwest corner of the house but would get afternoon sun in summer.

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S Bengi

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Is it possible to make more/all of your furniture out of the same materials that made your mold-free high-humidity bathroom?
Maybe they are both made from the same material but they went thru a different "curing" process?

Maybe you unconsciously wipe down and clean your bathroom more than your furniture in the back storage room? Maybe you use and ventilate the bathroom more than you ventilate the "back room" with the moldy furniture?

I think their are some things happening in the bathroom that we can replicate to the rest of the house.

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Mike Haasl

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S Bengi wrote:Earth sheltered wofati are wrapped in plastic on all 6 sides, so there shouldn't be a crazy amount of infiltration

I thought/assumed that they didn't wrap underneath them. If you could wrap under the bottom, that would help a bunch. Not sure how the "post and beam" construction would work if the posts are in disturbed soil? Unless you poke them through the plastic, in which case I think they'd rot...

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S Bengi

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This seems to have a membrane/plastic for the floor and also the roof and most likely the sides too. https://richsoil.com/wofati.jsp#:~:text=side-,view,-drawing

I think that if the post are connected by the subfloor, they will brace each other and it will work with no problem.

Roof: Earth+Membrane
Sides: Perspex (plastic/acrylic membrane)
Floor: Straw+Pallet+Membrane
SubFloor: Pallet

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Mike Haasl

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I re-read that link and I don't see a mention of membrane under the floor. There are two layers on top of the structure, one that wraps it fairly tightly to protect the logs and a second (the umbrella) that stretches out quite a ways around the building to keep infiltrating water away from the structure. I'm pretty sure there isn't anything under Paul's WOFATIs.

There isn't a subfloor either. At least not one in the sense of subfloors I'm familiar with. The support posts got 4-8' down below the floor and the rest of the logs are attached to them (walls and ceiling). Any floor is either earthen or is a wood floor sitting on that earthen floor. I believe...

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Kenneth Elwell

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I wonder if the entire build was done with "fill" versus "excavation" if some of the groundwater issues could be avoided.
If the walls (like Holzer's shelters) were in trenches (possibly on a sill), and a vapor barrier was on top of the "sub floor" and wrapped under the walls (into those trenches) and up the outside of the walls, then the walls would be on the "dry side" of the envelope. Add a vapor barrier over the roof and down the walls to seal it up, and add the "umbrella" over the top to keep the water from above away.

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