R-value of Straw Panels

R-value of Straw Panels

The May/June issue of

Environmental Building News was of particular interest to us, with its focus on the use of straw in building. We were especially interested, of course, in your comments on Agriboard.

While we were impressed with the article’s clear, accurate and objective overview, the comments on R-value of our product might create doubt in your readers’ minds about the properties and performance of our product. We would therefore like to clarify the situation with regard to R-value testing.

The tests that were quoted in support of our estimate of an R-value of 3.4 per inch (RSI/m 23.6) for Agriboard used the then-standard test method—the “guarded heat box method”—which has since been supplanted by ASTM C518, the “heat flow” method. We do not believe this change in method will have significant effect on the results in terms of measured thermal resistance.

Because we will be producing a compressed fiber board of somewhat lower density than the product tested earlier, we extrapolated the results obtained previously, which used board with densities from 16 to 18 lbs./ft³ (256–288 kg/m³), in order to estimate thermal resistance of the 15 lbs./ft³ (240 kg/m³) board we will produce in our new mill.

Based on this extrapolation of the earlier test results, we have every reason to expect that an R-value of 3.4 will be demonstrated when we have our product tested later this year using ASTM C518. The product tested earlier was virtually identical to the new Agriboard Industries core board, except for certain changes in the production process that should, if anything, improve thermal performance.

We admire and value the professionalism reflected in your newsletter; this makes us particularly concerned that your readers do not have the impression that we are making casual, unsubstantiated claims for our product.

Bill Thompson

Vice President

Agriboard Industries

Fairfield, IA

Editor’s response:

We are enthusiastic about compressed-straw panels and very much hope your projections of thermal performance prove accurate. However, based on our findings to date, including those described in the article, we believe an R-value of 3.4 per inch for a 15 lbs./ft³ straw panel to be quite optimistic.