Editing Earthship (section)

== Thermal performance ==
{{More citations needed section|date=June 2021}}
[[File:Solar Water Heater (5751093072).jpg|thumb|right|Solar water heater on an Earthship]]
Earthships rely on a balance between the solar heat gain and the ability of the tire walls and [[subsoil]] to transport and store heat. They are designed to use the properties of thermal mass and with the intent that the exterior earth-rammed tire walls provide [[thermal mass]] that will soak up heat during the day and radiate heat during the night, keeping the interior climate relatively comfortable all day. In addition to the exterior tire walls, some Earthships are sunk into the earth to take advantage of [[Earth sheltering|earth-sheltering]] to reduce temperature fluctuations.

Some earthship structures have suffered from heat loss into the ground during the heating season. This may be due to climatic differences between [[New Mexico]], where earthships were first built, and cloudier, cooler, and wetter climates. Thermal performance problems may also have occurred due to [[thermal mass]] being erroneously equated to [[R-value (insulation)|R-value]]. The imperial R-value of soil is about 1 per foot.<ref>{{cite web |title=Energy Extension Service: BUILDING ENVELOPE: Basement |url=http://www.engext.ksu.edu/ees/henergy/envelope/basement.html |website=ksu.edu |publisher=KSU Engineering Extension |access-date=5 February 2015 |archive-url=https://web.archive.org/web/20121027045557/http://www.engext.ksu.edu/ees/henergy/envelope/basement.html |archive-date=27 October 2012 |url-status=dead}}</ref> [[Malcolm Wells]], an architect and authority on earth-sheltered design, recommends an imperial [[R-value (insulation)|R-value]] 10 insulation between deep soils and heated spaces. Wells's insulation recommendations increase as the depth of the soil decreases (a negative correlation).

In addition to thermal mass, Earthships use [[Passive solar building design|passive solar heating and cooling]]. Large front windows with integrated [[Window blind|shades]], [[trombe wall]]s and other technologies such as [[Skylight (window)#Skylights|skylights]] or [[Steve Baer]]'s "Track Rack" solar trackers are used for heat regulation. Earthships are positioned so that its principal wall, which is nonstructural and made mostly of glass sheets, faces directly toward the equator. This positioning allows for optimum solar exposure. To allow the sun to heat the mass of the Earthship, the solar-oriented wall is angled so that it is perpendicular to light from the winter sun. This allows for maximum exposure in the winter, when heat is wanted, and lesser exposure in the summer, when heat is to be avoided. Some Earthships, especially those built in colder climates, use insulated shading on the solar-orientated wall to reduce heat loss during the night.<ref name="Reynolds"/>

Current Earthship designs like the global module have a "double greenhouse" where the outside glass is angled toward the equator, and an internal glass wall forms a walk way or hallway as you step into the Earthship. This greenhouse is primarily used to grow food; it also creates a barrier for the 'comfort zone' inside the house.