Cob: Thermal Mass Works, PAHS works, Insulation works

[Mark Piepkorn]

	Something tells me that lurking would have been a good path to stay on, 
and one that I'm going to return to almost immediately. I have tremendous 
lurking powers. I remember when Shannon started this list. Heck, I even get 
to bask in the glow of the auspicious distinction of having posted the 
first message that appears in the archives, back in '96. It was a request 
for more information in a time well before any of the (contemporary, 
USA-based) books on the subject came out. (In case anybody actually goes 
and unearths that message, I did subsequently get a copy of the Cob 
Reader.) All this time, and still so much I don't know.

	Like I indicated in my previous post, I'm not claiming to have any answers 
for anybody. There's no reason for anybody to believe anything I say. I'm a 
proponent of thorough research, and my hope is that presenting alternative 
information to the alternative information will inspire (or freak) people 
toward doing just that.

	No material or method exists in a vacuum.



At 03:01 AM 1/31/2003, Darel Henman wrote:
 >>The effect of the mysterious "thermal mass (wall) function" truly
 >>seems magical under the right conditions...
 >
 >There's certainly nothing mysterious about it.


	I used that word with my tongue in my cheek, but I guess that kind of 
thing gets lost in email. It was a poor word choice on my part. I should 
have said something more along the lines of "generally easier said than 
done." Also note that I was talking about the effect of uninsulated mass 
walls, not PAHS.



 >>but in practice varies from climate to climate, even building to
 >>building. This is also true of PAHS.
 >
 >The desirability would change from area to area but not the physics
 >behind it. Also PAHS allows you to tune the house, as I said above.


	Cob and other above-ground massive wall systems also allow for tuning. In 
many situations, they fairly demand it. Same goes for insulative 
approaches. The whole basis of appropriate design and materials use is 
rooted in "tuning"... which also usually includes "combining" and "weighing 
options" and "compromising."


	There are people who are satisfied enough when something seems to make 
sense to them despite not having been provided with all of the fundamental 
information, and/or when proponents of a thing artfully insist that it 
works. I'm not like that. (I'm not saying that you are, either.) I freely 
admit that the idea of PAHS is compelling to me. I want it to work. I'm 
willing to be convinced, and have been for years. Instead of just believing 
that it works, though, I need to be shown proof of concept. (This probably 
isn't the forum for it, alas, unless you can work in some cob talk too.) I 
keep thinking that RMRC is going to do it, but they never do -- and without 
it, I'm never going to pop the 45 bucks for their book, especially while so 
much other information contradicts it. It's a vicious circle.

	Independent data and the voice of experience always seem to show that 
insulating underground walls from the earth -- "charged" or not -- will 
create a more comfortable and thermally responsive living area. (Understand 
that I'm not talking about levels of insulation that completely stop 
thermal flow -- there's no such thing -- but enough so that it slows things 
down a nice bit.) The drawback is a somewhat diminished cooling effect 
during times of warmth -- but that same drawback becomes a benefit when 
it's realized that condensation on the walls becomes less of an issue. (In 
an underground house -- using PAHS or not -- the earth is cooler than the 
house during summer, which means that the walls are cooler than the air, 
which promotes condensation and mold growth in humid climates. A person 
could devise a desiccant wheel of some sort to deal with it... but, more 
likely, the occupants would end up running an electric dehumidifier 
nonstop, which is a significant load. Of course, the *really* smart people 
on this list would take advantage of cob's humidity-moderating and 
astringent properties by building a cob house inside their underground 
house.) (I'm actually somewhat serious about that.) (And to complicate 
matters, cement isn't allowed -- about which I'm completely serious.)

	Every indicator that doesn't have a scheme behind it describes the earth 
as an infinite heat sink. While large-scale charged mass undeniably has its 
benefits, direct earth-coupling in extended-cold winter climates invariably 
results in net heat loss over the season. Certainly it's going to be an 
enormously diminished loss as compared to being above ground in a typical 
modern house -- but it's going to be a rare bird that defies those laws of 
physics that we're so fond of by producing a zero-sum-conditioning 
structure, even with PAHS implemented, by maintaining a comfort zone 
acceptable to most people. Once it's established that a heat source is 
required, no matter how small -- and it's entirely possible that passive 
solar would do in a given situation -- suddenly the same results become 
achievable above-ground for comparable efforts and potentially less 
ecological harm via appropriate design and superinsulation.

	My point isn't that PAHS and underground don't work -- but that they might 
not work like people are often led to believe they do. (Much like happens 
with strawbale and cob.)

	Heat energy fed into the underground "heat bubble" doesn't just sit there 
waiting to get used up: it's constantly lost to deep cold, and to the areas 
outside the bubble. And it doesn't just travel out from the house in the 
summer, and then back to it in winter. Heat travels to cold. This is 
conduction. If the area outside the bubble (around and underneath) is 
colder than the structure, there will be more movement of heat away from 
the structure than toward it. This statement does take thermal gradients 
into account. Yes, there will be some movement of heat toward the structure 
as long as there's higher temperatures in the mass than that of the 
structure; and yes, as long as that condition exists it will lower the 
amount of heating required to sustain temperatures in a typical comfort 
zone inside the structure; and yes, depending on the climate and the design 
of the structure, passive solar could potentially overcome the heating deficit.

	Insulating the walls and floor of an underground house, in concert with a 
reduced-scale PAHS-type system seems to offer the best compromise of 
performance, embodied energy, ecological consideration, and initial and 
operating costs. It is, of course, going to be situationally specific and 
will need to be "tuned" just like anything else. The hope and the prayer is 
that the person doing the tuning doesn't try to do so without a full 
understanding and complete examination of all concerns and potentials. 
(There isn't enough money to hire me to do it. Well, there is -- but it 
would be dear, and I wouldn't offer a guarantee.)


	"Reduced-scale PAHS-type system"? For those who might not know, besides 
the U of MN research, PAHS is also an inverted derivative of the 
Frost-Protected Shallow Foundation method. HUD produced a design guide for 
the system several years ago, in which it was written, "An FPSF 
incorporates strategically placed insulation to raise the frost depth 
around a building, thereby allowing foundation depths as shallow as 16 
inches, even in the most severe climates. The most extensive use has been 
in the Nordic countries, where over one million FPSF homes have been 
constructed successfully over the last 40 years. The FPSF is considered 
standard practice for residential buildings in Scandinavia."

	This design guide, which has quite a bit of good, thought-provoking, and 
cross-applicable technical info, can either be purchased from Oikos for 30 
bucks:
http://oikos.com/catalog/Design_Guide_to_Frost_Protected_Shallow_Foundations.html
or read for free here:
http://www.cs.arizona.edu/people/jcropper/desguide.html
Your choice.


	Derek Roff of New Mexico, in a discussion of PAHS on another list, applied 
this line of reasoning:
"So how did you get all this high temperature heat into the ground during 
the summer? Some of it comes from the hot ambient air, and
the sun beating down on the ground surrounding the house. But since the 
ground surrounding the house has buried insulation right below the surface, 
the center of heat storage is your house. The idea is that the 
earth-coupled floor will pull heat out of your house during the summer, and 
pump it back in during the winter. This works great, if your house is 
really hot all summer. Or did you want your house to be comfortable in the 
summer, too? Remember, we don't just need to store a lot of heat, we need 
to store lots of heat at high temperature, and maintain it for many months, 
while conditions above and below are trying to suck it out."



 >> On the other hand, the effects of insulation are more predictable.
 >
 >Except when it gets moist, damp, or wet or the wind is blowing.


	*laughing*... Same goes for mass walls: soak 'em and they go haywire. And 
don't forget that wind on the surface of mass walls removes heat from them, 
too. (I do applaud you for wearing your biases on your sleeve.)

	Anyway -- the larger point you raise is precisely why most people desire 
to utilize materials in such a way that they don't perform less than 
optimally. I suspect that's a really big part of why everybody on this list 
is here: to learn how to best use cob.

	Using insulation? Design and execute so that the insulation stays dry, 
incorporate a continuous air barrier to help curtail the effect of leeward 
depressurization, stuff like that. Readily-available information backed up 
by building science and field experience. Simple. Common sense. 
Ecologically friendly. Upheld by the laws of physics.


 >> Above-ground, the best compromise in unspecified (that is, imprecisely
 >> defined) conditions for unspecified occupants is going to be
 >> diurnally-moderating insulated mass.
 >
 >Why do you call this the best. It's great for ares that have a high diurnal
 >differences, but not for areas that don't. In terms of saving the user money,
 >not to mention the environment it would make sense to employ thermal
 >storage for heating and cooling as much as possible.


	Read what I wrote. You often chide people for not following what you say 
closely enough; I'm afraid that I'm going to require the same level of 
attention to detail that you demand of others. I said, "the best compromise 
in unspecified (that is, imprecisely defined) conditions for unspecified 
occupants..." Speaking in sweeping generalities means knowing nothing about 
the specifics of things like the climate, local conditions, site features, 
occupant requirements (their requirements of the space, as well as the 
requirements of the space from them), etc. All things being equal in the 
sweeping generalities of things, it's a far simpler thing to design an 
insulated house that performs well in all situations than it is to design a 
mass-based house (above-ground or under) that will.

	Also, there's more to the moderation of diurnal temperature swings than 
climate alone, especially when it's insulated mass inside a conditioned 
space; sometimes it's wholly dedicated to an artificially-conditioned 
environment. (In this case, even warmth from the sun is considered 
artificial.) Too much mass, like too much glass, is a far less forgiving 
proposition than too much insulation when it comes to the performance 
expectations relating to the physical comfort of generic suburbanized 
occupants.


	Which opens up a whole 'nother can of worms about the need to get people 
to examine their expectations and understandings of housing and its 
relationship to the environment, and adjust their comfort zones and 
life-activities appropriately. When that happens, suddenly all sorts of 
potentially-significant options become viable to the general population.