Insulating with wool?

Photo by Rainer Ebert



Super insulated, air-tight buildings rely on high-quality types of insulation and lots of it.  Accommodating upwards of 12 inches in your wall assembly becomes a financial decision as well as a detail adjustment (i.e. double-stud walls).  Easily available, often sustainable products are made with cellulose (recycled paper), cotton (recycled jeans), spray-foam and fiberglass.

An uncommon type of insulation in the US is wool, but awareness is growing of its benefits.  If you are a fan of wool socks, then you know that wool breathes! 

This is important in deterring the growth of mold in cavities, but there are many other positives. It's a non-toxic material that can be installed without gloves and respiratory protection.  When treated with Boron, a naturally occurring element, wool also offers pest resistance.  Wool is naturally flame resistant; the industrial form, industrial felt, has long been used in machining processes and does not support combustion.  The raw material can be manufactured domestically (although places like New Zealand and Australia with huge sheep populations produce tremendous quantities).  Production of wool is both rapidly renewable (sheep coats grow back) and recyclable.  Most importantly for energy-efficient buildings, wool is an excellent insulator.  Here's an overview of thermal resistance (R-values):

R-4   = 1" WEKA Panel
R-12 = 3" WEKA Block
R-13 = 3.5" Batts
R-19 = 5.25" Batts

So, for 1 inch that's R-3.5 to 4 compared to R-2.9-4.3 for fiberglass and R-3.4 for cotton.  For a comparison of other sustainable insulation types, check out the Sierra Club's Green Home site. The US Department of Energy maintains comprehensive insulation information at Energy Savers.

Both batts and rope stock are available from Good Shepherd Wool Insulation in Interlaken, NY.  A board form was developed in the South Tirol of Italy by Walter Tasser.  Known as WEKA, both panels (R4 @ 1 inch) and blocks (R12 @ 3 inches) are available stateside through Tasser Clean Tech, LLC.   Any product pricing can fluctuate and quotes should always be obtained at a relevant time to construction, but at the time of this writing a ten-pack of 1 inch 2ft x 4 ft panels is $169 or $2 per square foot and a 30-ft roll of wool batt is $55.50 or $1.85 per square foot.  Compare that with $0.40/sf for fiberglass or $0.80/sf for cotton batts.

Cost is clearly a primary factor in wool's small market share, but I'm still intrigued by the panel and block forms.  Unlike loose-fill and flexible batts, rigid forms of insulation are not subject to settling over time and subsequent potential loss of effectiveness.

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