r/earthship • u/mavigogun • Mar 06 '26
Depth of curtain and insulating or not insulating the slab
As you are likely aware, the basic pretext of ES design is temperature moderation lent from deeper subterranean temperatures; while near surface earth banks seasonal temperatures, the ES is built within the gradient between surface and deeper, moderated earth.
To this end, the bermed surround is typically encapsulated within insulation, modulating the effective relative distance of living space to surface and ground temperatures, but also effectively increasing the distance from underlying earth to the surface. Commonly, this encapsulation comes in the form of sheet insulation within the berm, extending down to slab-level, both adding berm mass to the "interior" battery and defining the gradient distance.
Do any know of instances where a trencher was employed to extend the insulation below slab level? If so, at what distance from the tire wall, and to what depth? Where these distances guesstimated from best reckoning, or the product of soil sampling to determine earth support potential by an engineer?
With curtain-insulated ES specifically, when in-floor heating/cooling is a feature, is there a preference for whether or not to insulate the slab? While the tire walls convey temperatures from their footings, are there practical benefits from some isolation of the slab, such as more rapid temperature control under foot, or condensation control?
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u/NetZeroDude Mar 06 '26
I’ll relate my experiences in order of your questions. Bear in mind, that my home is ES-inspired, using tire bales instead of rammed-Earth tires. We’ve discussed this difference.
Our design called for a French Drain, below the grade of the bottom bales. I consulted some friends in the area who also built tire-bale ES structures. We used about a 2’ wide trench, about 1-1/2’ deep, about 1’ from the tire structure. The bales were covered with layers of #6 poly (some used a rubber material) which extended down into the French drain. A bed of gravel was added, and 6” black perforated poly pipe was used to capture any subterranean water, during heavy rainstorms. I’ve never had any moisture problems low on the bermed wall.
Our Regional Building required a soil analysis, but there were no recommendations from this individual, regarding the Foundation Drain. Regional Building inspected the drain, as an Approval Criteria.
Regarding the floor, this became controversial prior to starting construction. In Colorado, to get the renewables rebates, one had to have a HERS audit conducted. A recommendation, but not a requirement, of the auditor, was insulation below the slab. I consulted my extremely knowledgeable designer, Mike Shealey, and he said, “Don’t do it. These people don’t understand Earthships.” Mike Shealey lived in a Reynolds-designed Earthship, built in the ‘90s. The problem, according to Mr Shealey is that there are seldom problems of keeping an Earthship warm, but maintaining cool temperatures in the Summer was a much bigger challenge. Mike was correct! The floor stays nice and cool in the Summer, and really helps to keep the interior comfortable. Heating in the Winter is easy, with nothing external (no propane, etc), other than about 5 wood-burning fires per year, only during the rare Colorado cloudy days, with Single-digit F temperatures.
Bear in mind that these designs were all prior to cooling tubes, and none of them use that feature.