Energy Performance of Straw Bale Buildings

Infrared image showing heat loss in a home.
Infrared image showing heat loss in a home.

“Earlier this year, my colleagues Ace McArleton of New Frameworks Natural Building, Ben Graham of Natural Design/Build, and I conducted extensive blower-door testing, infrared thermography, and a series of moisture tests (probe, pin, and scan) on seven different buildings we had built in part or whole over the past seven years in Vermont and New York. We have just published the findings of this research in a report, Final Report for Energy Performance of Straw Bale Buildings Research Program. This research was conducted in support of a book by Ace McArleton and myself, The Natural Building Companion: A Comprehensive Guide to Integrative Design and Construction, to be released by Chelsea Green Publishing in the spring of 2012.

You can read and download the complete report at this address:

We welcome any feedback you may have about the report, and encourage you to distribute the report to colleagues, media outlets, or others you may feel would benefit from or take interest in this work. Keep up the good work, and have a safe and happy new year.”
Warmly, Jacob Deva Racusin
New Frameworks Natural Building, LLC

I’m glad to see their report because testing is so important in order to design and build better buildings in the future. While this report is on straw bale buildings, many of the same principles apply to earthbag and other building methods. The information is particularly relevant to those who are going to build in cold, humid climates such as the northeastern United States. $30 spent on a book filled with practical tips like in this report could easily save homeowners many hundreds of dollars. Here are a few excerpts.

“We frequently, but not exclusively, use lime as both interior and exterior finishes because of its durability.

– The primary locations of air leakage were in roof assemblies. Of these, significant or repeated bypasses included:
1) around chimneys and plumbing vent stacks
2) around blocking between rafters on the exterior
3) where tongue-and-groove ceiling/clerestory wall paneling extends through the envelope to the exterior as soffit material
4) at framing transitions where air barriers (such as air-tight drywall or gaskets) were either non-existent or inadequately detailed

– Windows and doors were also consistently leaky. These leaks occurred:
1) between the plaster edge and the window framing/trim, particularly on older buildings with less-thorough air fin detailing
2) between the rough opening (R.O.) and the window sash where foam sealants were inadequately installed
3) within the window units themselves, especially in salvaged windows but also in new windows
The most significant and widespread thermal bypasses occured in situations that could have been avoided or easily fixed, rather than systemic failures of the design.

Design is critical: A thorough and comprehensive design process is essential to ensure a building’s overall thermal performance. Results for nearly every project clearly show that non-straw bale components of the envelope were most responsible for thermal bypasses in the buildings.

Convection leads to moisture: There is a direct correlation of convective losses and increased moisture concentration, particularly in the upper half of the structure, as evidenced repeatedly by elevated moisture content in exterior readings taken in air bypass cracks in plastered straw bale walls.”

Energy-efficiency Upgrades by Owen Geiger

8 thoughts on “Energy Performance of Straw Bale Buildings”

  1. I am writing to inform you that, thanks to the great diligence of an informed community, a couple of errors were brought to my attention in the recently-released Final Report for Energy Performance of Straw Bale Buildings Research Program. Namely, the pressure rating of the blower-door test was listed as 50 kpa, not the correct value of 50 pa. Also, references to the moisture content of the wall were at times erroneously referred to as measurements of relative humidity. These corrections have been made, and accordingly I have attached the revised version of this report for your reference. My apologies for the inconvenience, and my gratitude to the eagle-eyed reviewers who caught these mistakes.

    Jacob Deva Racusin
    New Frameworks Natural Building, LLC
    P.O. Box 15, Montgomery, VT 05470
    (802) 782-7783 (c)
    (802) 326-2209 (h)
    (no attachment — please contact Jacob if you want the revised report)

  2. Nothing like haveing super insulated walls but the roof? I remember seeing a vault shaped building and i liked how the straw bales covered the whole building.
    I thought of straw bales recentley when i read an article on how yavapi county didnt adopt some newer international building code because the r value was so high they couldnt put enough insulation between the studs.So they were useing old codes that were doable.


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.