Subject: passive solar greenhouse/strawbale

From: Andrew Erb <[email-masked]>
Date: Fri, 7 Nov 1997 14:45:59 -0600 (CST)

I think the reference to the straw bale passive solar greenhouse was 
excellent, I have recently developed an interest in straw bale 
construction and hope to use it to build my own house/greenhouse, I found 
a very nice new book about straw bale construction at our public 
library.  

I once read that someone was using rabbits in their greenhouse, they 
provide heat and fertilizer, rabbit manure is supposed to be usable 
whithout composting (please correct me if I'm remembering this 
incorrectly).

---

From: [email-masked]
Date: Mon, 10 Nov 1997 08:46:22 -0500 (EST)

In a message dated 11/9/97 2:41:03 PM, [email-masked] wrote:

>The web page (if you want to find it do a search on solar strawbale
>greenhouse) to which I referred has a description of how the
>straw bale greenhouse used earth tubes to preheat or precool air depending
>on the season which also dehumidified the air.  It also has an eloquent
>peice on how the use of solar greenhouses will allow people to grow their
>own food and reduce the impact on the earth from all the transportation
>currently used to transport food. I would be interested to see the design
>plans for this greenhouse.  Also, in reading the book "The Strawbale
>House" I have learned that you can use a variety of plasters to put over
>the bales, creating the surface of the walls, probably even concrete which
>could be water proofed, thus reducing or eliminating the concern about
>humidity causing the bales to decompose.  If anyone is interested in
>strawbale construction get a copy of "The Strawbale House"  it has the
>answers. 
>
>Once again Dan H. Thanks for all the info on using rabbits/animals in 
>greenhouses.

No problem, I need to be reminded I know about this stuff as I get older.

I still recommend skepticism about the durability of strawbale as a
greenhouse wall.  Bear in mind that we are talking mainly about endwalls with
a span, normally, of about 12 feet often tapering to nothing, depending on
the design of the greenhouse, which SHOULD be dictated by climate,
availability of reflective surfaces on the ground, etc.

Now I have to be a party pooper again.  All practical, applied experience I
have heard about with subterranean air intake tubes has been dissapointing to
horrifying.  Dissapointing because the tubes don't really temper the air all
that much and horrifying because, where there are large temperature
differences with the house warmer than the soil, the dehumidification
mentioned leaves moisture in the tubes (That's where it goes) as condensate.
 Besides dumping large amounts of heat in phase change, which of course
negates some of the effectiveness of the cooling, the moisture often, if not
invariabily, promotes growth of molds that sooner or later cast spores that
have very bad effects on human health.  The only practical and lasting
remedy, other than digging a number of 6x6x3 foot holes equaling the
population of the building, is to plug the tubes that you installed at great
expense and difficulty.

This system is not alone in this difficulty.  There are otherwise very, very
efficient rock thermal mass storages, where air circulates through the north
wall (Northern hemisphere) which is filled with rocks of about the same
size*, then travels in the same sort of tubes discussed above back into the
greenhouse.  This is phenomenal for buffering cloudy spells.  Alas, it is
also a phenomenal place for those awful molds to grow.

In case this seems trivial to you, be aware that mold spores can really,
really make you sick.  You don't drop dead, you just languish and grow
weaker.  Anyone who has experienced or witnessed chronic candida can attest
to the evil effects.  If you start with a superhuman immune system, it just
takes longer.  Don't find this one out for yourself.  In addition to a
devastated immune system, general decline in the functioning of a number of
organs can happen.  

OK, it would seem as though the mold problem were soluble, but this is a
place where we want to have research grants, build laboratories, and gather
10 years experience before subjecting humans to living in these conditions.
 I shudder to think how many people out there with languishing health are
thinking, at least my solar home works, no realizing that it is the cause or
a major contributor.  We must all be aware by now that immune disorders are
epidemic, apparently due to the stress of toxins, lack of security, and poor
diet of modern life, as well as emotional distress.  I'll let someone else
rant on that.  I'll only say that I thought my wife was dying (probably was)
of apparently intangible cause untill we found someone who understood that it
was immune collapse due to chronic candida, a common disease immune weakened
people.  Knowing what to do, it takes years to recover to the point of a
reasonably normal life.

Regarding vapor barriers, yes, they should be on the warm side of the wall
which is on the interior in climates where the heating load is greater than
the cooling load.  It appears best to leave the vapor barrier out of walls
between the attached greenhouse and the building to which it is affixed.  I
suggest that you re-read that sentence, it is important.  The other thing to
remember is that it seems virtually impossible to create a complete, 100
percent effective vapor barrier, if the actual research done is any
indicator.  So to a great extent it is a vapor channeler, with concentrations
of condensate where the barrier leaks.  Naturally, in time vapor barriers
will spring more leaks.  Murphy is everywhere.  

The insullation I recommend in cold-winter North country areas is sawdust
mixed about 20:1 with masonry lime.  The lime eliminates insects and rodents,
again probably not 100%.  (100% is probably a conceptual fiction when applied
to processes and large populations.)  The sawdust is a fairly good insulator
even when wet, and the lime keeps it from rotting until it can  dry.
 Cordwood construction (stackwall) with the dawdust/lime fill is a good
greenhouse wall in these situations.  Probably you want to stucco interior
and exterior walls to counter air leaks ("infiltration" is how they say air
leaks in the books).  If you do a good job, air leaks are almost invariably
caused by checking of the cordwood and nothing else.  There are techniques
for eliminating this, or at least reducing it.  Since walls are most likely
to check in summer when it is not so important, you can take your chances and
see if your wall needs stucco by August or so.  This means that you can set
up your greenhouse that much sooner, bearing in mind that maybe you need to
be able to get at those walls.  

Straw bale is a great addition to the permaculture tool box and has many,
many appropriate applications, particularly where people grow grain in
quantity anyway.  In the north woods, it can be questionable for a number of
reasons.  I am reminded of people taking a short workshop in the southwest
who went about putting in swales indiscriminately just tearing up the earth
because swales are a good thing.  I saw one design in which the "swales" were
certain to promote erosion.  Every tool that sometimes works is a good one.
 We need to take the trouble to find out when each is appropriate and not
promote any technique indiscriminately, not even mulching.  Proper
permaculture involves knowing a lot of things and being a good designer.  The
earlier one is in the process of gaining that knowledge and skill, the more
conservative s/he must be to avoid doing harm. At the beginning of the
permaculture movement, Bill promoted beginners finding some working
arrangement with experienced designers.  Nothing ever came of that, so far as
I know.  But it is still the only proposal I have heard of that will spare us
a lot of trashing about doing more harm than good by using useful techniques
in inappropriate ways or circumstances.

For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since
1982), Elfin Permaculture workshops, lectures, Permaculture Design Courses,
consulting and permaculture designs (since 1981), and now correspondence
courses via email.  Next live training:  Paraguay, Sept. 1998. Internships
available. Copyright, 1997, Dan & Cynthia Hemenway, P.O. Box 52, Sparr FL
32192 USA  [email-masked]  

We don't have time to rush.

---

From: Bruce Brummitt <[email-masked]>
Date: Mon, 10 Nov 1997 09:05:55 -0600 (CST)

It was written:
reasons. 

by Dan Hemenway...
******************
We live in the northwoods of northern Minnesota, near the headwaters of the
Mississippi River.  We built a strawbale studio 4 summers ago for Cheryl's
holistic health practice.  We have only glowing reports to give on its
performance and esthetic appeal.

You mentioned "a number of reasons" strawbale can be questionable
here...please shed more light on this...

Bruce

Bruce Brummitt and Cheryl Valois
<[email-masked]>
"With Liberty and Justice...for All"
Lilac Moon Experimental Living Center

---

From: "April Sampson-Kelly" <[email-masked]>
Date: Tue, 11 Nov 1997 13:14:25 +1100

Dear bruce, what is your rainfall there?  I would love to do the same but
have moderately high
rainfall.  1200mm - what kind of foundations did you use?
thankyou for your post,
april

April Sampson-Kelly ADPA,BCA,MCA,GradSci,PDC
LC permaculture Visions
[email-masked]
http://www.ozemail.com.au/~askpv
GOOD PLANETS ARE HARD TO FIND

---

From: Bruce Brummitt <[email-masked]>
Date: Mon, 10 Nov 1997 23:59:57 -0600 (CST)

----------
From: "April Sampson-Kelly" <[email-masked]>

*********

>Bruce
*********
Our annual rainfall is just under half what yours is at less than 600 mm (23
inches).
The strawbale studio is built post and beam and the roof erected before
bringing the strawbales into play...that way they were not exposed to
possible rainstorms prior to enclosure.  A concrete footing is waterproofed
beneath the bales.  The roof has 3 foot (1 metre) overhangs all around to
act as a grand umbrella.  The bottom metre of the outside wall has
waterproofing material placed over the bales prior to application of stucco
exterior, which helps to protect from "splash".
See "The Straw Bale House" by Steen, Steen and Bainbridge...published by
Chelsea Green.

Bruce

---

From: [email-masked]
Date: Tue, 11 Nov 1997 09:06:43 -0500 (EST)

>here...please shed more light on this...

1)  It is not a place where a lot of straw is produced.  Wood is produced in
woods.  Therefore wood is in abundance and more appropriate, all things being
equal.  Given the proven performance and durability of cordwood (stackwall)
construction, which leaves the biggest and best trees in the forest and need
only thin what would be crowded out anyway, this is another suitable
construction method.

2)  Heated cold climate structures invite rodents.  Straw bales invite
rodents.  The combination is a compelling invitation to rodents.  Strawbale
construction sometimes uses bales as bearing walls.  It would be difficult to
replace infested sections.  This would be less difficult where post and beam
construction and strawbale infilling are used, but still one does not look
forward to routinely replacing walls.

3)  The humidity issue is very serious, I think, both as a potential
compromise of the insulating value of the wall and as a promoter of decay
organisms, particularly fungi.  "Grow shiitake at home!"  :-)  North woods
means humidity, or it would be north prairie.  As previously posted, vapor
barriers on easy to seal surfaces fail to an extent that they are being
discontinued in some recommendations where experts feel that the vapor
barrier may do more harm than good.

4) I cannot imagine a straw bale bearing wall that will not be compressed
beyond acceptable limits by a heavy snow load of say two feet turned to solid
ice by spring ice storms. Anyone who has live in a genuine winter climate
long enough has experienced this.  Of course there are perfectly sound ways
to build with straw bale, as merely a weather barrier and not as load
bearing, that avoids this problem.  

>From a performance viewpoint, the humidity factor is the one that most
concerns me in humid climates.  This would not show up in initial performance
but in deterioration of performance over time.  I'd be delighted to learn of
proven techniques that avoid this.  Of course in the climate where I now
live, straw bale would be reduce to termite frass in about two years, I
reckon, without horrifying doses of toxins.  

There is a good argument to be made for houses that function at the forest
edge for a certain period of time and then melt back into the soil.  You
could pull out your windows and throw a beech nut in the mess and move out
ahead of the successional line of forest again.  While a lovely way to live,
and reminenscent of very joyous tribal lifestyles, it is a bit tough in a
world with 6 billion people needing some space to lie down once a day.  Alas.
 I first heard this very permaculturally appropriate idea from Jack Henstridge
, one of North Americas two cordwood experts, in referring to cordwood using
clay instead of concrete as binding material.  He figured 20-30 years for
such cycles--I'd guess 5 to 10 years for strawbale deliberately managed in
this way.  I don't know how strawbale will hold up in a humid climate where
we do everything we know to preserve it except to apply toxics.  Frankly, I
doubt anyone does. 

Also in today's email was a private note from someone on this list who has
access to a published research report on strawbale performance.  Since I have
not read it, I should not repeat hearsay.  However I am hopeful that this
prod will get him to summarize the report for this mailing list.   Please?

To repeat, since it is easy to lose sight of context in these exchanges, I am
convinced that strawbales have many useful applications in shelter.  I have
seen brilliant hot beds and cold frames put together with them in Kansas and,
copying that idea, took it a step further and used them as a growing
substrate, as described in Kourik's edible landscaping book, after the need
for hot beds was past.  Later they were pretty well on the way to compost and
I used them as mulch.  That was a wonderful system.  In Georgia, I couldn't
get straw and tried the same with hay--a total disaster.  The hay has too
much nutrient and melte d away before the plants were an inch high.  A cold
frame that changes shape rapidly is tough to close off when zero F
temperatures are on the way.

Again, if people have proven solutions to my concerns, lets hear them.  As a
designer, I can only recommend what I know works and I have no business
recommending anything that is a question, even a small question, in my mind.

We don't have time to rush.i

---

From: "Eugene F. Monaco" <[email-masked]>
Date: Tue, 11 Nov 1997 12:08:23 -0500

There is a strawbale discussion group that has beaten this moisture issue
to death, and then some.  While there are some experts doing lab testing of
various wall sections, with and without vapor barriers, there seems to be
three schools of thought.

First, let me say that there are examples of 100-plus year old straw bale
homes in humid climates, particularly in the UK where it was supossedly
first contemplated. Sstraw bale and it's sister, cob, which is straw mixed
with clay and sand, generally does okay if it's stucco'd, and (read well)
sheltered from rains via an overhang.  If you keep the rain off the wall
the straw will tend to stay dry.   Fungi thrives in moist, acidic
condidtions (forest floor), and the use of lime-based stucco along with low
moisture, tends to cause an alkyline condidtion which keeps fungal rot
within tolerable levels; tolerable being 30 to 60 years life span, note the
pyramids were not made of straw bale, also note that most conventional
apartment houses are only designed for 30 to 50 year life span.

So the three schools of thought on vapor barriers are as follows:

First, is the use of a vapor barrier as Dan H. explained, on the humid side
of things to keep the moisture out of the wall.  Think of your hot steamy
kitchen and bathroom.  There you'd want it on the inside of the wall.  But
what about days when its dry inside (maybe a fire going) and it's humid
outside.  Then it seems as if you'd want the VB on the ouside.  Most
conventional thinking and construction practices put it on the outside;
they even shrinkwrap the house with a product called Tyvec.  In my
experience as a disaster recovery consultant, I've seen rotted walls
(conventional studs and drywall) at guess where?  The bathrooms and
kitchens.  If it were me I'd put a double VB at the bathroom and kitchen
(inside and out) to keep the moisture out of the wall.  But we all know the
moisture migrates doesn't it?

So that leads to the second school of thought which says, install a VB on
the outside as well as the inside. Slick but expensive.  Also, as anyone
who has dealt with stucco in Florida knows, when it rains, the stucco gets
wet, then it dries.  But in Florida they're using stucco over concrete
block so the block doesn't rot, but it can get dank in there unless you
have AC.  There is a product, genererically called EIFS (Exterior
Insulation Finish System), also known as Dryvitt, or Sto, that has as it's
final layer, a waterproof final coat which beads off the water and doesn't
get wet.  These layers of 'mud' are applied over exterior rigid foam
insulation, held together by a fiberglass mesh.  It allows you to shape
things and get architectural detail which is why it's popular.  The final
coat being waterproof is one of it's claims to fame.  Not to be outdone,
the paint industry came up with a product called elsatomeric paint which is
like painting your wall with rubber.  It's elastic, a polymer, easily
patchable and, if you can stomach the toxins produced from the entire paint
industry in general, not a bad product.  It will waterproof the outside; so
there's your exterior VB.  Slap one on the inside of the wall, or just at
the bathroom if you're in a bind, and you've got your double VB wall
section.  The theory is that you just flat out don't let moiture in.  But
you better keep the bales dry during construction.  And of course there are
the leaks.

The final and I think best approach is to forget VB's all together and let
the wall 'breathe'.  Forget plastic VB's, elastomeric paint and the like. 
Just use a lime-based stucco on both sides, and keep the roof overhang in
tact.  The moisture will migrate through the walls and not do all that much
rotting in a reasonable lifespan.  Of course don't try to impress an
up-town yuppie with this system, it might be a little close to the earth
for them.  But it's inexpensive.  I'd still install a VB at the toilet room
if there were showers in there, and design for good ventillation where the
interior humidity was high.

Having said all this, let me close by saying that in general I don't like
straw bale for the eastern US, mainly due to the totally unsustainable
agricultural methods in which the wheat straw is produced.  If you drive
through southern Ohio, and parts of the midwest where they grow this wheat
straw, it is a monocultural nightmare--the most devistated land I've seen
in these parts.  It's difficult to justify purchasing straw from these
farmers.  If one were to grow one's own wheat, organically, or
permaculturally, Fukuoka style, one would want all the biomass to be
returned to the site and mulched, not hauled off as if a surplus to build
houses.  But then again, we're in transition, it's all relative, and there
are trade offs.

Below is subscription information for the strawbale discussion group.

Regards,
Gene Monaco
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
East Tennessee Permaculture  ([email-masked])
Herbs, consultations, & training for total health and environmental
sustainability
PO Box 11851, Knoxville, TN  37939      (423) 457-4354
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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---

From: Bruce Brummitt <[email-masked]>
Date: Tue, 11 Nov 1997 19:46:25 -0600 (CST)

You wrote:
----------
From: [email-masked]

...  Heated cold climate structures invite rodents.  Straw bales invite
rodents.  The combination is a compelling invitation to rodents.  Strawbale
construction sometimes uses bales as bearing walls.  It would be difficult
to
replace infested sections.  This would be less difficult where post and beam
construction and strawbale infilling are used, but still one does not look
forward to routinely replacing walls...
 ...I cannot imagine a straw bale bearing wall that will not be compressed
beyond acceptable limits by a heavy snow load of say two feet turned to
solid
ice by spring ice storms. Anyone who has live in a genuine winter climate
long enough has experienced this.  Of course there are perfectly sound ways
to build with straw bale, as merely a weather barrier and not as load
bearing, that avoids this problem...  

For Mother Earth, Dan Hemenway, Yankee Permaculture Publications
*******
Some of what you wrote, you wrote out of ignorance.  There is much available
information that you can access as to the concerns you voiced.

I have seen log end structures that were built around here that have rotten
log ends that is permeating throughout the walls.  I have remodeled
"traditional" stick frame buildings that were insulated with fiberglass
batts, that no longer contained batts, but just little fiberglass mice nests
down at the bottom plate.
I've "jacked up" log cabins and replaced the bottom 3 or 4 courses of logs
with stone foundations.

Cheryl's studio is available by appointment to be seen and touched.  It will
last at least a lifetime, I'm certain, as will a log end  or a stick frame
structure built with attention to detail.

As to whether utilising straw as a building material is appropriate as a
form of permaculture...from a purist viewpoint, probably no.  As to whether
using straw in the northwoods because it doesn't normally grow there,
well...purists may say no.  There are plants that I encourage to grow here,
that aren't indigenous...and yet I use them as food.  I'm not certain that I
could sustain myself in the manner I wish, otherwise.  I do make use of wild
rice, native herbs and plants, deer, grouse, etc., but I supplement my diet
with my garden.

Our home is earth-sheltered and built from logs and stones gleaned from this
land.  I much prefer this place as a home.  As a teaching tool, Cheryl's
studio has great value.  The straw that was used is grown near here.  All of
our buildings use photovoltaics for electricity, another non-native.  I read
books that were written in English and in Spanish...both not indigenous to
these northwoods.

Out of curiosity...where do people on this list walk on this permaculture
path?
I'd like to hear what other folks build their buildings from, how they heat
and light them, what they eat, etc...

Learning, always learning,

Bruce

---

From: [email-masked]
Date: Tue, 11 Nov 1997 22:45:25 -0800 (PST)

>"With Liberty and Justice...for All"

It's the old rat infestation and bug hotel conversation again.  Reminds me
of when I first started building earth sheltered houses when everyone talked
about how damp, fungi filled, and dark it would be, which would be true if
we left out ventilation and windows.

There are many structures of straw in Europe that have been in existence for
over a hundred years and are not any more prone to collapse from mice mining
than are stick frame, or adobe structures.  It's all in the care and skill
of the builder.  With thoughtful and careful design straw bale is a
wonderful material that will outlast the builder.  There are structures
standing in Nebraska continuously occupied for over 80 years.  And as far as
I know they have mice and fires and bugs in Nebraska so someone did
something right.

My concern about any material is if by taking it for one purpose we are
impoverishing the environment.  So is straw more important as a carbon and
biomass source for the soil where the grain is grown or is it more important
as a building material thus saving forests.  I think that this is a serious
question and I am slowly reaching the conclusion that sustainable forestry
would be more ecologically sound than straw harvesting for construction.
Unfortunately sustainable forestry is not how most timber is produced.

Certainly I would rather see straw bales in a wall than going up in smoke
where most of the worlds' straw is presently going.  It seems that in my
area of the southwest the best material is adobe or rammed earth,
particularly if you set aside the topsoil and makes bricks out of subsoil.
The problem with this is how do you insulate for cold winters.  I have not
seen a truly elegant solution to this problem, primarily because it either
requires building two walls with a hollow core for cellulose fiber, or
straw, etc. or using  styrene/urethane exterior insulation.  One solution
doubles up your labor and materials to a profligate level and the other
contributes to the petro-chemical pollution madness.  

So my wife and I are in the process of building with straw bale exterior
walls on the north, east and west with adobe interior walls for solar mass.
We am incorporating a Russian stove, or kacheloffen for backup heating
because we can coppice the existing trees on our place for fuel.  Solar heat
comes from south facing windows and an interior greenhouse.  The house is U
shaped with the greenhouse in the opening of the U.  We are using the Watson
wick system of waste disposal which means all our grey and black water is
held in a gravel or pumice basin under the greenhouse from which we hope to
grow tropical and semi tropical plants in addition to the occasional tomato
and pepper.  There will also be some Btu benefit from water temperature and
some storage benefit also from the water soaked basin. 

We looked at many options before making this decision and even though we
couldn't reach that 100% purity level we feel that we have made the best
decision for the environment in which we live.  A big problem is the
regulatory agencies which one has to deal with who are intent on making
construction of a home part of the great industrial process.  The Universal
Building Code, to my mind is an oxymoron - how can it be universal?  We are
forced to build foundations to counter frost heave which doesn't happen here
in Santa Fe, NM.  Maybe it makes sense in Minnesota but there are structures
here, including the oldest house in the USA which are build on field stones
laid at near grade and they haven't moved in over two hundred years.   Tom
Watson, (see Watson wick above) is anxious to challenge the regulators and
the national building codes with a civil suit claiming the right to housing
a civil right and that regulation and codes make it impossible for those
with little or no money to have housing.  I have to agree with him.  Most
construction is over engineered and eliminates the possibility of
innovation.  At one time in the recent past Texas had no regulations on
dwellings unless they were built with commercial use in mind.  If you wanted
to build a house out of refrigerator cartons it was your house and you had
to live in it and if it didn't endanger you neighbors it was ok.  That seems
sensible to me.

On materials I think that Pliny Fisk III of Center for Maximum Building
Potential has the best criteria.  His system is based on a data base of your
biome which lists all of the resources and from this data base you are able
to put together the best possible materials for you environment.  It may be
bamboo if you are southern coastal, or adobe if you are desert southwest.
Mainly it is a system of careful observation of the region and then good
design based on the cleanest ethics you can evolve.

I agree with Gene Monaco on vapor barrier that is I am not using them.  I
much prefer breathing walls which transpire over the annual cycle.  If you
design your shower to spray on the walls then you will have a problem - but
that isn't inherent in the materials but in poor design.  I prefer a shower
in the greenhouse where the humidity serves multiple function.  Problem with
exterior vapor barrier is that any moisture is trapped exactly where you
don't want it in the strawbale or in your insulation if you are building
with sticks.
Scott

P.S. I built first straw bale construction in Belarus (53 latitude, 29"
rainfall, 90-97% relative humidity) two years ago. Construction is used as
livestock barn, and of course doesn't have any heating system. So far it
hasn't created any problems, including mice invasion in walls. It holds very
nice temperature in winter (last year - minus 30 F) even with no insulation
on the roof and simple one glass windows. Seems to work fine even in such a
harsh enviroment!

ARINA
*************************************************************************
<[email-masked]>
Permaculture Institute
Scott & Arina Pittman 
PO Box 3702
Pojoaque, NM 87501

Ingenio Patet Campus

---

From: [email-masked]
Date: Wed, 12 Nov 1997 09:00:32 -0500 (EST)

In a message dated 11/11/97 1:27:03 PM, [email-masked] wrote:

>moisture migrates doesn't it?<<

OK, first, that is NOT what I said.  I recommended, if you really think you
can do a good vapor barrier, do it on the warm side of the wall.  I said
nothing about humid.  Warm air holds more moisture than cooler air, even if
its relative humidity (RH) is lower.  As the air moves through walls, and it
always does, even through cement walls, it often goes from warm to cool,
particularly in the higher portions of a room.  As it does so, it cools
(remember in this example it is cooler outside) and therefore moisture begins
to condense.  When the temperature difference between the interior and
exterior of the wall or wall cavity (depending on construction techniques) is
very great, the condensation is very, very significant.

No one seems to be able to construct a perfect vapor barrier, even in
laboratories.  (Accepting that someone will probably point to a study I've
missed to the contrary.)  Where vapor barriers leak, they tend to funnel
moisture and the effect of condensation is worse than usual, I've read.  I
don't see why this is so, but even ordinary condensation will be bad enough.

Again, it is the termal difference, not the moisture difference, that
predicates the best place to put a vapor barrier, if you are going to use one
anyway.  In Wisconsin or Michigan, you would alwas put it on the interior of
the wall, no more than 1/3 of the way into the wall.  Here in Florida, the
vapor barrior goes to the outside of the wall, as it would in an equatorial
desert.  Because the warm side varies with attached solar greenhouses day to
night, I recommended that the vapor barrier be left out between the
greenhouse and the rest of the living space.  This is normal--do not use
vapor barriers on interior walls.

There is a kind of construction where you have a 2x6 stud wall on the
exterior and then put up a 2x4 interior wall right inside it, giving you a
total of 8 inches (minus the usual amounts that the lumber companies cheat
you unless you buy dimensional lumber) of insulation.  In these walls, in
cold-winter climates, the vapor barrier is put on the interior of the six
inch wall, so that it is not breached when running conduit, etc, for which
the interior 4-inch wall serves.  

Tyvek and related materials used to wrap the OUTSIDES of houses are NOT
(repeat NOT) vapor barriers.  These materials are wind retardants.  While
sufficiently porous to pass water vapor, they are also more or less
impervious to air currents, so the wind does not penetrate the wall.  This
material is far more useful than alleged vapor barriers and highly
recommended.

If you are going to use plastic sheeting as a vapor barrier in straw-bale,
obviously you do not slap it up against the bales themselves because they are
prickley and will puncture the bales.  Thus you need a stud wall inside the
bales to hold the plastic away from the bales, and you probably need to cover
this with a smooth material such as gypsum board.  Add all this to the cost
of your wall.  
Stucco finish with a vapor varrier paint is probably more reasonable.  Paint
that is an effective vapor barrier is of course way more expensive than
ordinary paint.

It is nice that two buildings in the UK have made it 100 years with
strawbale.  I wonder what percent of the total buildings of strawbale in the
last 100 years that is.  There are 1,000 year old cordwood buildings, too.
 But I'd say 20 percent of that is a more reasonable expectation.

Again I am concerned that we are promoting strawbale with a zealousness that
might better be reserved for judgement day or something.  No one technique or
material serves all situations.  Permaculturists need to evaluate materials
based on experience, bioregional appropriateness, available construction
skills, other cultural preferences, and detached common sense.  I am very
enthusiastic about the potential of strawbale, but I see that potential
threatened by overenthusiasm that may apply this technique where others are
more appropriate.

Issues such as this are why it takes many long years of experience to become
a good permaculture designer.

---

From: "Eugene F. Monaco" <[email-masked]>
Date: Wed, 12 Nov 1997 22:20:47 -0500

Message text written by INTERNET:[email-masked]
walls on the north, east and west with adobe interior walls for solar
mass.<

Scott,
Just curious, what would you think of cob in place of the adobe for the SW?
 It seems to have both thermal resistivity and thermal mass, although labor
intensive?
Gene

---

From: [email-masked]
Date: Sat, 15 Nov 1997 21:29:16 -0800 (PST)

> It seems to have both thermal resistivity and thermal mass, although labor
Wish I had direct hands on experience with cob.  From what I know and the
cob structures I've seen I think it is a good material for the southwest as
well as the damp climate of England.  I can't imagine it any more labor
intensive than adobe.  I think the secret of all of these structures, straw
bale, adobe, and cob is having good overhang - particularly if you are using
clay straw or just clay plaster.  I can't think of a good reason to use
cement on these structures if we are going to the trouble to build
ecologically.  Cement certainly ain't!
*************************************************************************
<[email-masked]>
Permaculture Institute
Scott & Arina Pittman 
PO Box 3702
Pojoaque, NM 87501

Ingenio Patet Campus