Wofati in Canada?

The average temperature in Canada's capital (Ottawa) is a balmy 6 degrees Celsius (42.8 degrees Fahrenheit). Wouldn't a Wofati be really fuckin' cold? Even if the windows were open during the entire month of July (which averages 20°C), I can't imagine the thermal mass would get hot enough to maintain a comfortable temperature. Am I misunderstanding how this works, or is it simply not a viable design for colder climates?

That's how I understand it. Earth sheltered homes built in Ontario in the 70s, were almost always better suited to being root cellars. Cold along with major condensation. I think it would need to be insulated.

- I've been in dirt floor cellars where great care was made to Collect all rainwater into a concrete cistern and found that area remarkably dry -
I am willing to accept the Idea of the whole mass working as a Thermal bank holding the temperatures within several degrees warmer so that
the heat load placed on the house was then equivalent to a structure located further south- mid atlantic !

It will be interesting to see how They winter over THIS year ! Big AL

My S.W.A.G. (Scientific Wild Assed Guess) is that they don't have enough insulation to gain and retain enough heat over the summer to be comfy over the winter without a RMH, or other heat inputs.

This is based on my experience with 3 ground coupled superinsulated buildings, one in Ontario Canada, and two in southern michigan.

I extremely look forward to their results and hope and pray it goes fantastically well.

I don't have a wayback machine, but if my memory serves me, the definition of wofati has evolved somewhat over time. Insulation of the sheltered mass, as one would with a Hait inspired umbrella (PAHS) home, seems to have become minimized or abandoned altogether, now emphasizing the R-value of the dry dirt itself.

Imho, without sufficiently thermally isolating the sheltered mass from the air and surrounding soil, and R-5 of wood duff is nowhere near close enough (Hait recommended at least R-20), you are limited to whatever the average soil temperature for the area is at depth. Without that thermal break, any heat you add, through whatever means, passive or active solar, or fuel or electric fired furnace or boiler, will quickly dissipate into the vast heat sink that is the surrounding soil.

That may not be bad, if the that soil temperature is the temperature you want in the house, but even temps in the low sixties can wear on you, day in and day out, without at least some direct sun or spot heating. If you get it too far off, you may find yourself insulating the living space to keep the walls and floors from sucking out your supplemental heat.

Hait's PAHS homes were designed and built in Montana, with only slightly warmer temperature averages than Ottawa. A PAHS home built utilizing Oehler's building techniques and natural materials (except the moisture barrier, though a clay barrier could be use, but it can be a lot more problematic) ought to work fine (even into the Arctic with some more insulation, including underneath, to isolate from permafrost, and you may need to boost passive solar heat gain in Summer by using thermal solar panels and/or trombe walls). The tricky part is coming up with the right balance of insulation, mass and solar gain to give a comfortable, year-round, living space without the need for heating or air-conditioning.

If you are in doubt, but still driven to give it a try, maybe building a small outbuilding (or folly, which may be a more appropriate, if antiquated, term) will give you an opportunity to prove its merits in your area.

The tough nut to crack in modeling the thermal performance of one of these is the variable r-value of the soil and the presence/absence of soil moisture, which yanks the r-values around.

But without "Hait levels" of evil petroleum based high density foam insulation, it is unlikely they will achieve a comfortable temperature without significant heat input.


AND, I hope I'm just wrong and they all work great.

Andrew Parker wrote:I don't have a wayback machine, but if my memory serves me, the definition of wofati has evolved somewhat over time. Insulation of the sheltered mass, as one would with a Hait inspired umbrella (PAHS) home, seems to have become minimized or abandoned altogether, now emphasizing the R-value of the dry dirt itself.

OK this is news to me. I would love if anyone could point me in the right direction here. My understanding of the Wofati is that if you surround the building with enough thermal mass it will hold the energy from one season through the next. The idea being that inside you will maintain a steady average. You don't have to build an air-tight, insulated building if you are surrounded by enough earth.

Did this not work out with the Wofati prototypes that Paul (et al) built?

Sawdust is available for free in many parts of Canada. If I were to build such a structure, I would give it a very big overhang plus some sort of soil liner around the house, to keep the sawdust dry.

 Cedar,  and sawdust from other evergreens,  can persist in dry soil for decades without decaying. It's a far better insulator than dry earth would be.

Troy, I am not sure that the R-value of the soil is a factor, once it is isolated. In fact, a higher R-value could be a serious impediment to the soil's ability to act as a thermal mass. Water is only a negative in terms of its heat conductivity, and only when it is in contact with water in the surrounding soil. One variation of PAHS is to isolate underneath, as well as on the top and sides.

One need not use petroleum-based insulation to achieve R-20 or higher, but nearly all "permanent" alternatives do require energy to produce. If it helps, you can consider the energy that will be saved over the long term. "Temporary" non-petroleum alternatives might include wood chip or straw -- clay coated, mineralized or otherwise. Earth lodges in the northern plains often included a thick layer of straw under the sod roof. Earth lodges were temporary structures, usually not lasting more than ten years (I have been in some tract homes that looked pretty seedy after ten years), but who knows how long they would last with an evil petroleum-based waterproof liner.

I also hope they work great.

O, I would suggest you read Paul's article on the wofati, the PAHS information is still there, just not prominently displayed.

You can put all the dirt you want around a house, but the temperature will never be more or less than the average temperature at that depth for that area, unless you isolate it. For me, without insulating the thermal mass, a wofati is just an oehler home. That does not mean that there are no benefits to an Oehler home, but I don't think you can get through a cold winter without supplemental heat.

I think that Paul is experimenting right now. That is his prerogative. I hope that he is able to prove his hypotheses.

Sorry, didn't mean to be unclear...

I am not opposed to thoughtful use of petroleum products like dow High density foam. I used a bunch of it in my super insulated shop here in Michigan, and my superinsulated house in Ontario.

In some of the discussions, the idea was floated that the use of petro-based foams was undesirable for various reasons.



I hope that the Wofatis work well without the use of styrofoam, but doubt it.


It is a careful balancing act to get enough thermal mass around the house, and isolate that mass from the surrounding soil with insulation, and keep it dry.

Troy, I guess I should have used an emoticon, , but as my son likes to remind me, I am too old to be doing that. There are quite a few idealogues here at Permies (it is about permaculture, after all). You need to be very conscientious and tread lightly, at times. I used to have 5 apples.

I would like to try perlite as an underground insulation. If you buy a semi-trailer-full, and you would need about that much, it is price competitive. The liner is a problem and I have been in a couple of discussions about clay and clay-based alternatives. There are some interesting geotextile-clay products in the liner industry, but I don't know what the cost would be. I have also advocated going with a Burdei style basement house with thick thatch and/or superinsulated roof, instead of a green roof, to reduce costs and complication. I don't have Paul's charisma to convince others to experiment for me (I guess I am a passive-aggressive world domination wannabee). I might get around to building one, eventually, unless I can browbeat one of my kids into doing it sooner.

I too have long been concerned about the viability of an earth-mass-coupled house in colder (and especially moister) climates. The incoming solar radiation needs to enter the soil in summer considerably faster than heat conducts deeper into the earth from the mass, as it will be moving down all year as well as moving out to the winter air. The lower the average ground temperature, the more severe that constant loss will be. My family house in upstate NY has an uninsulated concrete and cinder block foundation, open on the east face to a hillside. In the summer, the cellar would always be chilly and damp, and if air was allowed to blow through it would even condense on the undersides of the floor joists as well as walls and concrete floor.

Builditsolar.com has some useful information about soil temperatures for the US:
Ground Temperatures as a Function of Location, Season, and Depth
One item is that it isn't until you get to 12' depth that the annual temperature range diminishes to ~10F min to max. At 5', you still see a range of ~22F.

Another item is that the temperature lag is not as great as one might wish, with maximum soil temps at 5' occurring about early September, and at 12' about late October. The minimum soil temps occur at 5' in March and at 12' in April. The dates may shift a bit later in dry soils, I don't know for sure.

Finally, the average annual soil temperature for a given location fairly well tracks average annual air temperature, and especially average well water temperature. So for a colder location, the earth makes it that much harder to get warm.

The upshot of all this is that real insulation is going to be needed all around the soil mass, top and bottom, and in a colder climate the deep earth temperature might overbalance any gain that could be gotten from summer warmth. I think the viability of a wofati may be limited in cold climates to areas with very dry soils, which will conduct heat slower than moist soils.