Page 55 - October 2015 Green Builder Magazine
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IMAGE CREDIT: BRETT AND SUE COULTON
Alternative Approach. Straw bales do not have as high an R-value per inch as “conventional” insulating materials, but the walls www.greenbuildermedia.com 10.2015
are much thicker. Plastered straw bale walls also function as thermal mass.
DOUBLE DUTY
SOMETIMES THE STRUCTURE is the insulation. This greater thermal mass (higher proportion of clay). Some
is true of many “natural” building systems, such as “hybrid” systems incorporate rigid foam insulation to ramp
straw bale, solid wood, rammed earth and clay- up the insulating value of walls; for example, rammed earth
straw, although it’s important to understand that the builders in cold climates often sandwich rigid foam between
insulating value of each varies. In general, straw bale has a reinforced rammed earth walls.
greater insulating value than earth-based wall systems, but
even the R-value of straw bales varies with the type of bales These materials also have low embodied energy and tend
and the degree of compression. to be sourced locally and finished (when necessary) with
natural materials such as earthen plasters. But although the
With systems utilizing these natural materials, R-value is material cost tends to be much less than “conventional”
just part of the story. They also function as thermal mass, counterparts, the cost of labor is often higher.
absorbing and slowly releasing heat. In a house with good
passive solar design, this thermal mass can effectively Structural insulated panels (SIPs) and insulated concrete
regulate indoor temperatures. Some systems—clay-straw, for forms (ICFs) represent other building systems in which the
example—are flexible enough so that the mix can be tailored structure incorporates the insulation. Both SIPs and ICF
for greater insulating value (higher proportion of straw) or construction create airtight building envelopes; ICFs also
have the advantage of thermal mass.
as an alternative to plastic foam. But wood fibreboard, which has rock wool boards you can drive on and glass fiber you spray into
some of wood foam’s properties, has been around for some time overhead spaces are examples of products that have long been
and fills a niche role in the market. Finally, we’re still keeping our around and are slowly gaining traction,” he says. “But there are
eye on Ecovative’s Mushroom Insulation, which is not yet widely few new products. Aerogel and vacuum panels are too expensive
available. for buildings, and it will take a while before that changes, if ever.
With insulation, it is the use and installation of the products that
Straube suggests that the emphasis should lie more on the is important and exciting.” GB
application of the product than the product itself. “High-density
