We get a lot of email from people who read the blog. I’ve never really tracked it, but I am guessing that we get more email in response to our posts than comments on the actual blog. Usually, I try to respond privately … I assume that if somebody does not want to comment or question in a public format that is their right.

However, I am noticing that many questions asked overlap, AND that I often repeat myself in these email discussions! So, I will continue to respect the privacy of the email we receive; I will not post names or private information (unless I ask in advance), but if it makes sense to me I will respond to questions asked publicly. It is often the case that more than one person was thinking along the same lines …

I’ve been asked lots of questions about the temperature inside the earthship this winter. A few days ago, I got this question from the Netherlands,

… did you guys manage to get the earthship nice and warm already? I’ve read about the rocket-mass heater and it being about 5 celcius inside 🙂 That’s too cold for me 🙂 Don’t think my house will stay around 20 celcius in the winter here as well, planning on a ’tile heater’, some kind of thermal mass stove hanged with thick ceramic tiles.

And, even more recently the following email came in from Manitoba,

… can [earthships] obtain enough heat through the thermal mass/solar gain (of course altered in construction for our location) to maintain a comfort level in the home with out extra or external heating source (that includes wood stove) in our climate … [I am looking for] technical information on the floor thicknesses and composition. honestly anything that pertains to the heating, storing of heat and Insulating yes …. the floor … any links pointers you have or connections would be greatly appreciated …

Now, I am of the opinion that the thermal mass of the earthship has already proven itself successful in our building.  With no additional heat source the earthship has maintained an above zero temperature all winter.  We are currently experiencing -10 degree Celsius highs during the day, and (you guessed it) the temperature inside is still above zero.  Currently, the temperature seems to hover around 3 degrees during the day and drops a degree at night.  When we do operate the rocket mass heater (not surprisingly) the temperature in the building goes up.  We have not run the heater consistently or long enough to figure out how well it does, but do not expect that it will do a great job at warming the entire building as it does not distribute its heat outside of the room it is in.

This is the first house project I have worked on (or lived in) where I have not worried about an unheated space during the winter; the waterline has not frozen and burst, it is comfortable enough to work inside whenever we decide to, and I am able to store freeze-sensitive building materials inside (caulking, paint, whatever).  Down the road this means that without any further modifications we could turn off the electricity, lock the door, leave for our month long Caribbean cruise, and come back to an intact building.  The tilapia in the fish pond would probably be dead, but there would be minimal (hopefully zero) maintenance costs associated with leaving this building uninhabited for a period of time.  In contrast, I have fond memories of un-freezing the waterlines in my inhabited, conventional house if the power failed during cold winter temperatures, and the waterline to my chicken coop has frozen yet again this winter!  (As an aside, a small, propane torch is incredibly effective on frozen water lines … just be careful where you point it!)

Obviously, the current inside temperature is not a livable temperature.  Bear in mind that we have poor solar gain in December and January.  I can count on less than two hands the sunny hours we have had since December 1st … we have gone over a week at a stretch with overcast skies.  To make it worse, what little solar gain we are getting right now is largely blocked by our temporary living quarters.  When the sun does hit the south face of the building the transformation is as amazing as it is pleasant … the inside temperature climbs quickly and becomes quite comfortable (into the teens).  The thermal mass of our building has not been warmed above surrounding earth temperature this winter, and the inside temperature reflects that.

We plan to have an additional heat source to compensate for our overcast skies in December and January.  Our intention is to put radiant heat water lines in the floor, and run heated water through our floors.  We have lots of waste wood available locally, and it is justifiable (in my opinion) to burn this wood for energy.  I am hoping to generate electricity through wood gasification and will have lots of waste heat as a result.  My intention is to use this waste heat to charge the thermal mass of the earthship (via the waterlines mentioned above).

There are many different ways to address staying warm in colder climates.  Mike Reynolds and the Earthship Biotecture crew are simply not interested in needing an additional heat source.  The ‘Global’ earthship model is their answer to colder climates (indeed any climate).  The global model uses a double green house wall, a rigid insulation thermal wrap outside of the tires, and floor insulation under habitable areas to more effectively trap solar gain so that the heat does not bleed away in colder environments.   In very cold climates they even talk about a third greenhouse wall.  A discussion of most of these ideas is available from Earthship Biotecture in their DVD set 2009 Earthship Seminar.

We have used the concept of thermal wrap and plan to use floor insulation  in our building, but bear in mind that this does not address an environment with limited solar gain.  As stated above, we plan to heat the thermal mass of our floors with wood and compensate for lack of solar gain.  Earthship Biotecture is investigating other passive heat sources; the body heat of the occupants, heat from compost, and unintentional heat sources such as the waste heat generated by a laptop running in the building.  There are some very interesting ideas presented in the DVD set mentioned above, and I will be curious to see what progress is made on them.

Another interesting idea is to simply store the solar thermal gain from warmer months so it can be used during the colder months.  For example, my radiant heat flooring could get its heat from solar tubes on the south face of the building, store the heat in deep (insulated?) trenches under the floor (or close to the building), and draw on this stored heat in the colder months.  I do not claim much knowledge or experience with this idea, but it certainly seems worth exploring.

I do believe that Earthship Biotecture is correct that a livable temperature can be maintained (even in cold climates) without additional heat sources.  As stated in the above DVD they have successfully been able to maintain a temperature in the vicinity of 20 degrees Celcius in their buildings.

Frustratingly, the assorted North American Building Codes do not view this as success.  For example, our BC Building Code specifies that a building must maintain a temperature of at least 22 degrees Celcius in its living spaces (9.33.3.1. Indoor Design Temperatures).  A passively heated home simply cannot obtain the precise temperature control that can be achieved with fossil fuels or wood or electricity.  The building code does not mention what happens if the power goes out … it’s all a matter of perspective.