Building a cinder block earth ship in east texas

Hello,

I am thinking about buying some property close to a town in east Texas and building a cinder block earth ship. Exactly the same layout as an Earthship. Replace tires for Cinder blocks, and have a professionally pored foundation.  It's pretty humid in east Texas. The issue i have read is that the earth thermal mass surrounding the houses causes moisture build up in the house, and then mold.

My Question is this:

If i used cinderblock instead of tires, and put a foot of thermal barrier between the thermal dirt mass and the cinder blocks, would that fix the condensation problems? Not going for 100% recycled, going for off grid potential.

George

Hi george,

Welcome to Permies.

The condensation is from the walls being cooler than the air... which is what you are looking for if that is how you want to keep your house cool in the summer. So in my home, I have an earthship style tire bale home, we use fans to move air around which helps remove humidity. We also use a mini split as a dehumidifier for the house when the humidity is too high inside.

Welcome to the forum!

The way an earthship is designed is what causes the humidity.

Earthships have a built-in water system that provides water for the gardens.  This is where the humidity is.

https://permies.com/t/52058/Earthship-greywater-systems

Hey george, welcome to permies!
I think placing a thermal barrier between the earth and the cinder blocks  would negate the advantage that a mass of earth earth is supposed to give in a passive solar house.
Earthship designs that I've seen have a large amount of earth inside their insulation and moisture envelopes and even more bermed up outside of that.

A simple way to incorporate earthen mass into a cinderblock building in a way similar to an earthship,might be to add a room at the back wall and fill it with dirt.
In this scenario, the insulation layer could be inside the the cinder block walls, and the "dirt room" inside of that.
This is not unlike a trombe wall, only trombe walls are usually depicted directly in front of a wall of windows, with the living space behind them.
Earthships show their tire wall holding back soil at the rear of the design and the living space is in front of that.

Making room for thermal mass inside the cinder block walls takes up expensive square footage.
You might be able to expend the thermal envelope to incorporate soil bermed against the exterior walls.
By putting the insulation and moisture barriers on the slopes of the berms, and protecting them with geotextile, soil and plant life, you can get more thermal mass for less money.
The idea is that you have a large mass of dry earth thermally connected to your living space and the earth below to mitigate extremes in temperature and humidity.
I think you will want active radon mitigation/monitoring, but I'm not sure.

Practically speaking, I suggest building cinder block walls with carbon fiber geotextile incorporated as tie-backs.
The geotextile tie backs should allow the berms to be steep and stable with a minimal extra expense.
Adding tiebacks to the wall after the fact might be very expensive.

In a humid climate, depending on the character of the soil and water table, it might not be practical to keep a mass of dry earth even if shielded on top. If the soil in the berm wicks up water from below, it will be pretty much at ground temperature year round and not store heat in winter. If you can isolate the thermal mass earth from groundwater, you can get good tempering action.

What if we graded the soil to drain way from the wall and pinned a moisture barrier to that slope, before adding the berm itself?
Of course if we thermally isolate the bermed earth from the soil beneath it, we might be loosing out on net temperature gain.

This brings up a question: do soil tempatures under an 8 foot pile of dirt equal soil tempatures at the bottom of an 8 foot deep hole?
That is to say, can we access more stable soil tempatures that exist by piling up dirt instead of digging?
I think that we can, to some extent.
When we measure soil depth it's from grade down,  so if we change the grade...

A moisture barrier would not by itself thermally isolate the mass earth from deep earth temperature. Depending on the climate, deep earth might be too cool to be desirable to include in thermal mass. It will always be considerably cooler than room temperature in a climate with serious heating needs, so you would not want it well-connected there. If subsoil is always fairly dry, it will naturally conduct slowly and allow heat to build up in the mass. If it is moist clay, it will conduct heat fast enough that it would be counterproductive as thermal mass.

A berm built above original grade would in time alter the subsoil temperature profile to match the new grade level.

Exterior Humidity/Vapor Barrier on all 6 walls.
Interior Humidity-source Venting (misty showers/bathtubs, stove/oven, laundry-dryer)
Interior Humidity Removal (dehumidifier, ac with the fan on low speed)
Intake Air (use a ERV to remove some of the humidty as in comes in while also venting the bathroom)

Indoor Graywater Filter System (greenhouse), this could be diverted to an outside unit during the hot mold season.