[Strawbale] OSB or Not? (rendering versus sheeting)
derek at unm...
Mon Dec 6 19:45:42 CET 2010
--On Monday, December 6, 2010 6:10 AM +0100 "Sport Hotel, Jure Pozar"
<jure.pozar at gmail...> wrote:
> Dear All,
> I have in interesting information. I have spoken to a guy who does
> natural plastering for over 20 years and he said that the houses in
> Austria which he worked on 20 years ago show problems now. The
> plaster which was applied directly to the strawbales on the outside
> is cracking and falling off and they found out because over the
> years some moisture got inside the straw and made it crumble and
> dissolve. So the house is no good now and there is no easy way to
> repair it. I wouldn`t like my house to live the same misfortune in
> cca 20 years time. This is why vapour barrier and wind proof facade
> is a good solution. I can`t wait to hear your comments.
There is a common approach to making building decisions that yields
problems. It begins with the uninvestigated anecdote, such as, "I
talked to a guy who said...", or "I saw a house that had problems
because...". The information may have some bits of truth in it, or it
may be totally erroneous. For example, I don't know if there were any
strawbale houses built in Austria twenty years ago. Certainly not
many. Then we generalize the questionable information into one or more
general principles. Ignoring, among other things, the fact that the
first houses built with any experimental method or material are usually
built by amateurs, and illegally. And that we learn things with
practice. The problems of the prototypes tend to get solved with more
Next, we add more unsupported information- that "there is no easy way
to repair it." On the contrary, there is no plaster easier to repair
than earthen plaster. Lime plaster is pretty easy to repair, too. The
most widely used plasters, based on Portland cement, are among the
hardest to repair. However, they are used successfully in many cases.
Most problems with the bales themselves are fairly easy to repair.
Removing and replacing one or more damaged bales has been done on
multiple occasions, and the process has been photographed, written up,
and published in places like The Last Straw Journal. The process gets
harder, when the builder has decided to "improve" standard strawbale
construction via something like drilling holes through the bales, and
filling them with concrete, to "strengthen" the structure. If there is
large-scale failure of the bales in a given house, then this reflects a
significant design or construction problem, which could not have been
solved by plaster choices.
The final unfortunate step of this kind of thinking is often the
adoption of a new, untested approach, based on imagination and
supposition, which is conceived as a breakthrough solution. [Such
ideas may not be truly new. They may have already been tried, with
negative results, and therefore, are seldom seen. But they seem new
and clever to the builder.] Such ideas generally have unintended
consequences. Often, the thought is, "I will keep all the moisture
out." What this usually leads to is keeping excessive levels of
moisture in. An example repeated all over the world is the plastering
of earthen buildings with Portland cement plasters. Earthen buildings,
which survived centuries with properly maintained earthen plasters, are
covered with cement stucco "to protect them", and within a decade or
two, have major failures due to trapped moisture. Similarly, in wooden
structures, improperly designed or constructed vapour barriers have
caused major moisture, mold, and structural problems in millions of
houses around the world.
We can't build with perfection. The International Space Station leaks.
There has never been a structure built with more engineering skill,
more care, higher cost per square meter, or higher stakes for failure.
It is built the very best that we know how. It suffers no wind storms,
no buffeting rain, no earthquakes, and no loads, since the gravity
stresses are all equalized in a free-fall environment. Yet it leaks.
Let us not imagine that we can build a house that solves problems that
humans have never solved before. Rather, I suggest drawing from the
best ideas and most reliable solutions that have been proven in actual
construction and in rigorous testing. Most of want to build great
structures, and improve on what has been done before. I think that is
possible, and laudable. I think we can improve building practices and
methods by understanding what has been tried, and investigating new
possibilities that add on to, combine, or extend previous successes.
Or, more interesting to many of us, we can explore techniques which
simplify processes and minimize the excesses of conventional building.
Working more harmoniously with nature, rather than fighting her.
Making maintenance and repair easier, rather than imagining that we can
avoid it. New ideas and approaches are most likely to succeed, when
the mesh with the general principles of building science.
Attempting to innovate without careful study of previous successes and
failures is perilous. There are many failures among experimental
buildings. In part, because they are experiments. In part, because
the builders often do not study what has been tried before, and don't
test their innovations before applying them to a house. At the risk of
repeating myself, there are good resources and references available in
books and on the web, including: The Last Straw Journal
<http://thelaststraw.org/>, the Ecological Building Network
<http://www.ecobuildnetwork.org/>, Building Science
<http://www.buildingscience.com/>, Bill and Athena Steen's The Canelo
Project <http://www.caneloproject.com/>, and Andrew Morrison's
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm...
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