In the “Earthship 101” slide presentation, the second slide
says, “Imagine… living in a home that cost you nothing to heat or cool…” The problem with
this statement is that it is wishful thinking. The base water and power systems
required to run Earthships cost $60,000. Systems for heating, cooling, humidity control, and
ventilation are required in almost every circumstance, but
they are omitted from the Earthship design and therefore budgeting, because the
“Earthship controls its own temperatures.” While this is an admirable ideal, it
is not accurate, or even physically possible, which we will explain in some
detail throughout this book. Regardless, a traditionally-built home’s system
for mechanical, electrical, and plumbing costs around $35,000. So in buying an
Earthship systems package, the owner has paid a $25,000 premium to “pre-pay”
for water and power. The problem is… an owner of a traditionally-built home will
spend somewhere around $20,000 over the life of their home to buy water, gas,
and electric from utility companies. That means an Earthship owner pays a $5,000
premium over and above what a regular grid-tied user will pay over the lifetime
of their home, plus they still need backup heat, additional solar panels and
batteries for some locations, as well as humidification controls and cooling in many locations.
Furthermore, Earthships commonly use propane for domestic hot water, cooking,
and supplementary heating, as well as some form of gas generators for backup
power for cloudy days. These are not free and those
costs are not factored into the vast majority of budgets.
Because Earthships are not designed for their specific
climate, they tend to have hot and cold spots. The
Earthship literature tells us that “the average temperature in an Earthship is
70 degrees.” That sounds really comfortable, right? Except that temperature is
based on an average of 365 days. The research and experience of many owners tells us that up
to 70% of those days will include extended periods of over and under-heating - an Earthship is often hotter than
comfortable between 10am and 7pm in summer and colder than comfortable between
7pm and 9am in winter.
Principles of a solar oven – why Earthships overheat
There is no other way to say it: Earthships, especially
those with slanted glass and no overhangs, tend to overheat. Even in
the winter. Many Earthship owners will say that even when it is -10°F outside
and snow is blowing sideways in 40mph gusts, they will
have to open up all the windows to cool their home off enough to be
comfortable. That might be okay for a while. However, as we get older, or as
our hands cannot crank windows and vents anymore, as we tire of stopping what
we are doing to get up to open and close windows twice a day, or when we have
to get snow off the windows when its freezing cold… this becomes a relevant
maintenance issue.
A substantial amount of scientific research has been done on thermal performance of Earthships in varied American, Australian,
and European climates. We will share some overviews of the findings by these
researchers later in Chapter 2, but the consensus is that Earthships overheat
as much as 9 months a year, depending on location. Earthships also under-heat
in northern latitudes due to cloudy conditions, colder inner-earth
temperatures, and the fact that earth-sheltering is designed to be used for passive cooling. That means
supplementary ventilation, dehumidification, and/or
heating need to be
considered basic requirements for the Earthship to work. Most of the time,
these additional systems are installed after the build, which can lead to
unsightly additions that were not accounted for in budgeting. Acknowledging
this early allows us to address these issues in the design phase, where we can
make the intrusions fit beautifully into the home and plan for the financing to make it all work.
We know now why the buildings overheat, which is great
because it means we can do something about it. Earthships, when they use
slanted windows and no overhanging roof, are designed like solar
ovens. The buildings are oriented to true south, and the slanted windows allow
in too much sun. In the summer, the greenhouse can be stiflingly hot and humid. The heat is
not quite as sweltering in winter, but neither is it comfortable. The
temperature in the greenhouse can be “unbearable” as some owners have stated,
swinging between 45°F and 95°F depending on the season. A shade cloth is often
required on the greenhouse in the summer to prevent overheating. If we design
this critical area correctly from the outset, we do not need that shade cloth
and can avoid overheating.
Many early Earthships did not use wall insulation. This is a problem, even in
Taos. Some builders these days are insulating their Earthships, and/or putting
a line of insulation as a secondary wall 4 feet outside the tire walls. The extra insulation costs
money, uses more unnatural and unsustainable resources, and takes more time to
build. Plus, it is yet another system that can fail. The issues that cause the
need for these extra materials can be addressed with good design that speaks to
your climate.
In the winter, because there are not many windows in the north-side living spaces, the north
ends of the rooms stay at or near earth temperature, which is around 58 degrees
in Taos, but is much lower in other parts of the world. So you have to have a
sweater in part of the house and then strip to your skivvies to pass through
the greenhouse to another part of the house, where you will
need your sweater again. We also know now that supplemental heat is needed in
winter, especially in areas where it freezes. Earthship builders in cold
climates who prefer comfortable indoor temperatures are likely to a) install
floor and foundation insulation, and b) install a heating system. Foundation insulation is critical
because the cold can seep up from the earth and make spaces uncomfortable for
anyone not wearing socks and sometimes even insulated winter boots too. Radiant
floors, wood stoves, fireplaces
and furnaces are all common additions in colder-climate Earthships.
Even in the winter, non-vented Earthships with the
greenhouse open to the living areas can be stiflingly
hot. Supposedly, roof venting,
and the new earth tubes (which are not able to be retrofitted) helps prevent
overheating in the summer. However, this natural ventilation cooling technique only works in areas where
humidification is of no concern. In humid or dry areas, we
also need to supplement the tube and vent system with dehumidification (in
humid areas) or humidification (in arid areas). Otherwise, in a humid
environment, an Earthship will collect water along their interior wall
surfaces, forming a vertical pool for molds and algaes to grow. This often
occurs on the walls of the planting areas and edible plants end up being infected or overwatered. This is
an epidemic issue among the many Earthship dwellers who do not live in an
environment as arid as Taos.
This is why we discuss both active and passive thermal
comfort strategies in this book.
