[Strawbale] ecoville architechs: strawbale

Mon Dec 3 11:22:50 EST 2007

Thank you Laren,

this is in response to an earlier post from you, the message had bounced so now I see your posting in my strawbale list folder, my message rules put it there and I had not seen it until this morning.  I hope you don't mind my sharing this discussion with the strawbale construction list serve.

Yes, perhaps we should modify our website with regards the R-values of strawbale walls to conform to the official tests.  

Of course, we had a hard time getting ORNL to test strawbales at all since they are not a corporate "green" product and, since "government" is very much in the pocket of the corporations, we view such tests with some skepticism.  Our nations energy policy itself  is another example of government misconduct and deceit.

As far as there being more wood in a bale house, I would say it is possible but we've done 35 of them and find it to be no more and sometimes less.  As far as wider eaves go we recommended those long before we were doing strawbale walls as they will protect any siding and such finish materials are generally expensive.

We see strawbale as just another of the many options one can choose for walls. Only a portion of our clients request straw bale walls but we think it is a good choice for those who want that look and feel.  We've been doing homes for people since the late 60s and in the 70s began doing solar homes whenever we had clients who were interested.  Our bale clients like bales because it has had so little processing, its an organic material, they seem to want the thick wall aesthetic, and the natural lime/clay finish we use.  We like it too because with lime/clay stucco we don't need any control joints, even plastering across dissimilar materials, because it is a softer more elastic material.  The other thing about bale houses is that it has empowered owners to build  their own homes which as you know can be a savings as well.  We've had a good time helping people build their bale houses and the reports we are getting from our clients reflect a considerable satisfaction and that includes the energy efficiency of their homes.  Some of them were even surprised how well they did.  Of course the standards around installing the straw walls are critical, as you mentioned, especially in the details at windows and doors as well as carefully stuffing the top and bottom of each head joint in the wall.

I suppose I could critique just about any wall system, and we do critique industrial wall systems in our workshops, but we are very encouraged by the increasing interest in Green building and passive solar energy efficient homes as well as more earth friendly lifestyles.

I visited your website and appreciate anyone encouraging passive solar design.  Some of your homes look like they could be double envelope houses.   We did a couple of them back in  the 70s and found them to work very well also, despite the "science" that some used to critique them.  We lived in one we built out of salvaged materials years ago and I was very impressed with its performance.
###

This is an enquiry e-mail via http://www.earthandstraw.com from:
Laren <Larencorie at yahoo.com>

> straw bale walls are rated around R50,

Hello Howard,

Unfortunately, that is not even close to accurate. The Oak Ridge
National Laboratory tests are the most scientifically valid ones, and
are the most widely used and accepted. They say that the Rvalue
is R1.45/inch. The state of California rates them at R1.3/in. That is
a pretty good insulation value, since the walls are so extremely thick,
but on a 24ft x 32ft house, the additional wall thickness takes up
10% of the interior living space, that would be available in the
same size house, with the same Rvalue, using cellulose insulation.
The strawbale construction requires about the same amount of
additonal wood framing in the roof and overhangs, to protect
the bales, that would be needed to frame the cellulose insulated
walls.

Another factor that is virtually always left out in exagerated claims
of strawbale Rvalues, is that the deep holes through the walls, for
doors and windows create a lot of additional interior surface area,
which is only about half as far from outdoors, as the rest of the
interior wall surfaces. So, their Rvalue is that much lower. This
is a lot of thermal bridging. The same thing happens with floors
that are not insulated at both the interior edge, and the outside
edge of the walls. Even then, the there is a lot of thermal bridging.
Concrete, stone or earthen floors carry the heat right around the
bails, and/or, only partially through them. These design factors,
beyond the simple Rvalue, significantly effect the actual R value
performance of any thick wall system. I have found that, in
general, the increased roof size, over thicker walls, then beyond,
to create overhangs to protect the bails, uses as much, or more
wood, than is needed for wood frame construction with the same
interior area, and the same Rvalue. The bale walls add additional
cost and labor, with no gain, either monetarily, or in insulation, or
in living space, just more work. However, they do usually look
fairly nice. But, I contend that a comparable look can be fairly
easily obtained without bails, and their big negatives. Rounded
corners, and hand plastering can be done with wood framing,
too. BTW, the percentage loss of floor area is most profound
in smaller structures. In a big warehouse it will be insignificant.
For a 16ft by 24ft house, it means a 15% loss of floor area.

Quote:

"It is noteworthy that all tests of straw bale wall systems prior to the
Oak Ridge test in 1998 had potentially significant shortcomings and
should not be considered particularly reliable. The last Oak Ridge
test had no identified deficiencies and is considered by most to be
an accurate determination of the thermal resistance of straw bale
walls. ORNL determined the R-value to be R-27.5 (or R-
1.45/inch), or R-33 for three string (23") bale wall systems.
Shaving a bit off the top just for conservatism's sake, the
California Energy Commision officially regards a plastered
straw bale wall to have an R-value of 30. "
####

Now I want to address the concerns you mention in the post below.

I am aware that bales are insulation and not thermal mass, my understanding and experience with passive solar tells me one needs both insulation and thermal mass.  When a client wants a passive solar design I generally do go to concrete or an earthen floor for thermals mass but I've been pleasently surprised that even when it is not a good passive solar design how well the bale houses perform.  Of course we put an inch and a half of plaster on the interior surface, its very hard to get just a thin coat of plaster to cover the bales adequately.  

I totally agree with your comment on mechanical systems and think we should design to eliminate them as much as possible but in the south, and with people being sooo used to air-conditioning I haven't had too many clients willing to go without it.  But bale walls are at least as low tech as concrete, wouldn't you agree?

We have had none of the problems you mention after 30 some houses.  We did help a woman in Kentucky with a house in which she refused to follow our advice for details at windows and doors so she had severe leaks and of course the straw started to compost under the windows.  The owners were afraid of mold and could smell some so they brought in mold experts and discovered it wasn't the straw that was moldy it was a piece of old furniture that she had moved in so it was removed and the house rechecked for mold and they found none present.  Still, the house smelled like composting straw so remediation was needed to make it right.  I would argue that a similar problem would occur no matter what material you were using, if you've got water getting into your wall you will have an issue to deal with or it will begin to smell and attract insects.  We plaster/stucco our bale walls with a lime/clay plaster that keeps the critters out.  Any mouse trying to chew through will soon be deterred by a burning sensation in its mouth and the wet exoskeleton of a termite does not fair well either.  

A concrete house is very energy intensive to build, concrete has a lot of embodied energy so should be used only when necessary.  It is hydraulic cement and there are uses for it that are hard to beat using any other material.  When you do build with concrete, as with walls, you do need to insulate it somehow and generally that is done with foam.  Foam is generally a toxic material so we try and minimize its use.  Why polystyrene is considered "green" by anyone is beyond me.  It is vinyl and benzene, both powerful carcinogens.  

Resale value of bale homes is not bad at all, it depends of course on the particular house just as with any other material.
Yes bales make for thick walls, all our clients wanted thick walls and deep window sills so bale walls make a lot of sense for that.
We've not had issues with insects once the wall is encapsulated with plaster.  If we did we would not be using them in our own home.  We even left a wall unplastered for a few years to see what "issues" would arise and nothing insurmountable presented itself, the wall in the garage is still unplastered after 5 years.  I would have thought it would be full of rodents living in it but the cat must keep them out.  We live in the back woods of Tennessee and termites have not been any issue for us even though we refuse to use pesticides.  Sure straw will absorb moisture, if there is some present, but proper detailing as with any material keeps that from being any problem.  Concrete has some nasty characteristics with regards to moisture as well and is not the permanent material some imagine it to be either.  Concrete tends to crack and is very difficult to repair.  There are usually pros and cons to any building material but with proper detailing and use those problems can be eliminated.  Straw has been used for a building material for millions of years, by humans for at least a million, and because of its own unique properties will continue to be.

Building is a practice that humankind continues to learn about.  If we look at the homes that have lasted the longest on this planet, however, we discover that those built of earth and straw have proven to be the most sustainable as many of them have been continuously inhabited for over 1000 years.  The Taos Pueblo has been so for 900 years and counting.  Any building that people are willing to inhabit for that long is sustainable.  A home that has been lived in for that long, longer than it took to grow the trees it was built of, is a sustainable home.

We also believe that math, formulas and theory can only take you so far, you have to build, experience, observe and evaluate for yourself to really know.  It seems to me that you spend so much energy attacking strawbales you must feel threatened by them which doesn't make much sense to me.  Also climate specific design is important so while running cold water through your slab may work for cooling in arid Colorado it is a very bad idea in the South.  I'm sure you realize what happens when a cold surface meets warm humid air and we have plenty of that down here.

Apparently the website I looked at by goggling you name is a different and older one than the one with this article.  I like your HTM design on the recent one along with some good information for folks.  As I said I always appreciate anyone promoting passive solar design, it is basic information we should all remember and pass on.

Howard Switzer
www.earthandstraw.com 
931-589-6513
  ----- Original Message ----- 
  From: Laren Corie 
  To: howard at earthandstraw.com 
  Sent: Sunday, November 25, 2007 5:51 PM
  Subject: ecoville architechs: strawbale

  This is an enquiry e-mail via http://www.earthandstraw.com from:
  Laren Corie <natural at colorado.net>

  http://www.thenaturalhome.com/passivesolar.html

  Materials such as strawbales, rubber tires, wood, carpet, logs, ICFs, autoclaved aerated concrete and drywall, all effectively resist heat loss ("R" value), but they have very low energy storage capabilities (K value).   Strawbales just don't store any heat!   Sure, they insulate well, but in a passive solar home you need to store energy.   Strawbales would make fine insulation wrapped around an HTM, but don't use them for the walls' actual building material.   When heat is stored only in the home's furnishings and a thin coat of stucco, expensive mechanical solutions like radiant in-floor heating or a central forced air system become necessary.   Simplicity is the key to sustainable design.   We're not selling any high-tech solar gizmos here, HTMs have no "moving parts" in their HVAC system to break down, so you never have to call your friend the plumber to fix the heat pump or whole house humidifier.   We believe in a very low-tech approach to making your family comfortable.
  A common misconception is that autoclaved aerated concrete, strawbale and log homes have large thermal masses. This is simply not true. They have very low thermal masses as compared to concrete. 
  Thermal mass is a relative measure of an object's ability to store heat, "K" value.   The complete inability of strawbales and logs to store heat is what makes them such a poor choice for a passive solar home or an attached greenhouse!   People and plants alike are much healthier in a consistent, radiant heat rich, naturally lighted, AND WELL VENTED environment.   If your home is not storing the heat brought in through the windows quickly enough, temperatures rapidly become too high for your comfort and will eventually kill your plants.   That's why you'll never see an attached greenhouse like this on a strawbale home.   Airtight homes are bad enough to begin with, but straw, wood, and paper are fuels that promote black mold growth in moist, unvented locations.   Cracks in the strawbale plaster open the wall's interior to indoor air humidity.   Meanwhile, a surface bonded block wall is waterproof, can be further sealed with non-porous latex paint, and provides no fuel to promote
  exotic growths that could affect your indoor air quality.   Natural plasters are always an option for the concrete wall's finish coat, too, but keep in mind that they do not have the ability to create a non-porous, waterproof coating.   Building a home is full of important design choices.   Don't let your passion for the environment cloud your decisions.   Strawbales are often used by clients for insulation outside of their homes.   There is nothing wrong with stacking them around the exterior, under eaves, to help insulate.   Using strawbales for a permanent interior wall building material has endless problems, though: 

  The value of a straw home drops drastically. Why build with a material that has no resale value? 
  Straw bales are very wide. Why lose all that floor space and still get taxed for square footage? 
  Strawbales are a natural egg laying area for insects. Why take the risk and have to exterminate? 
  Straw realistically needs a timber frame support structure. What happens when termites eat the posts? 
  Straw absorbs moisture - plain and simple. Why use insulation that loses effectiveness when wet? 
  Straw is very easily destroyed by animals. Why would you invite mice and rats into your house? 
  Strawbales have no anti-mold properties. Why would you take a chance with black mold infections? 

  This bears repeating: strawbales are an option worth considering for INSULATION outside the home (stacking them around the exterior under eaves), but using strawbales for a permanent interior wall building material is not a bright idea in a passive solar home. Designs lacking thermal mass are simply not able to store passive solar energy properly.

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