Why do you use straw insulation?

Since 2021, we’ve worked on many projects with Croft, a prefabricated panel manufacturer from Maine. The cavities of their wall, floor, and roof panels are filled with straw insulation.

We use straw for a few reasons:

1. It sequesters a significant amount of carbon.
   While cereal grains like wheat, oats, and rice grow, they draw in carbon. Once the edible part is harvested, the bulk of the plant remains in the form of straw. Using it as insulation stores that carbon for the life of the building! (For every pound of carbon in the plant material, 3.67 pounds of C0₂ are pulled from the atmosphere.)
   
2. It’s a great insulator.
   Straw has an R-Value of 3.8 per inch of thickness (based on Croft’s approach). That’s comparable to EPS foam or cellulose.
3. It’s good (and just as importantly, it’s not bad).
   It doesn’t contain harmful chemicals like foam and it grows easily in the places we’re using it (so it’s accustomed to the climate and doesn’t have to be shipped long distances). 
4. It’s naturally fire-retardant and rot-resistant because of its high silica content.
   Croft has received a Class A fire rating for ASTM E84 at all densities.