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Re: GSBN:Ask the Experts
--On Tuesday, June 24, 2003 12:45 PM -0500 Chris Magwood
Here's a question that arrived in the TLS mailbox.
Do I use straw bale because of the insulation
abilities, or adobe earth for thermal mass, or a combination
thereof? The more I read the more I get confused and the longer it
takes for me to begin the actual project.
Does Last Straw have any writers that can help answer this question
with my region in mind, with explanations of why?
Here's my perspective on this question: Natural builders have
discovered, over the millennia, adequate, and sometimes elegant
solutions to housing in different climates. However, in current
times, our standards and available options have changed, in both good
and bad ways. Options which were sustainable when practiced by
millions, are often unsustainable when practiced by billions of
humans. Our minimum standards for space and comfort have increased
dramatically in the last fifty years, increasing our energy
consumption disproportionately. We now have effective insulation
options that didn't exist before the last century. For these
reasons, few of us natural builders want to build a typical 2003
house, nor a typical 1803 house.
In most climates, a comfortable, energy-efficient home needs lots of
insulation and thermal mass. High mass materials, like adobe, cob,
and rammed earth, do not have significant insulative value. Their
great mass can average out the daily temperature swings. If your
daily average is 70 degrees Fahrenheit (overly-simplified, a daily
high of 90 and low of 50), mass could be all that you need. In Baja
Norte, I would guess that during different parts of the year, the
daily average temperatures would be too high or two low to be
comfortable in a mass-only home. Adding insulation outside of
high-mass materials can be done, but it presents some challenges.
I am excited by strawbale, because it offers both mass and insulation
in an affordable, renewable material. Most people are aware that
straw bale houses have outstanding thermal insulation. Fewer people
recognize that a strawbale also contains significant mass. A
strawbale wall covered with a thick mud plaster, as many of us favor,
has about the same mass per square foot of wall surface as a standard
adobe wall. But the SB wall's effective thermal mass is higher than
an equal mass of adobe wall, due to the efficiency gained in
insulating the thermal mass.
A strawbale house with thick plasters and a high-mass floor offers
superior levels of thermal mass and insulation. No other
sustainable, affordable building method, as usually built, provides
an equivalent combination of these essential building elements. For
this reason, strawbale construction is a useful approach to
energy-efficient housing in many climates (assuming good design and
construction, including a well-insulated roof).
Language Learning Center, MSC03-2100
Ortega Hall Rm 129, 1 University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885