Q: I recently learned about a building material called Aerblock, an aerated autoclave cement building block that has been used in Europe for many years and is only recently available in America. Does it really have both mass and insulating capabilities? I understand that it’s inert as far as outgassing or causing allergic reactions, but I have some concerns about the overall embodied energy. —Allison Elliot, Paonia, Colorado
A: Autoclaved Aerated Concrete (AAC) is a new material to the North American market but has been used successfully for decades in Germany. It’s a strong, lightweight load-bearing block, somewhat like pumice, weighing about 25 to 40 pounds per cubic foot, compared with 130 pounds for standard masonry. It’s easy to work and can be sawed, drilled, nailed, and chiseled like wood, using woodworking tools. It offers a safe, highly fire-resistant structure and is both rot- and termite-resistant. The millions of air cells in AAC blocks, plus their thermal mass, make them natural insulators and very energy efficient. The material mass also gives walls excellent sound insulation.
As far as embodied energy goes, the ingredients (sand, lime, some portland cement and aluminum powder, gypsum and water) are on the high side, but AAC manufacturers claim they try to use recycled sources. From a health standpoint, ACC is an inert, nontoxic product that doesn’t outgas. However, some manufacturers use recycled fly ash, which can be radioactive.
Despite these advantages, it’s difficult to find masonry crews that are comfortable using the material. Hebel, one of the German originators that now produces AAC in the United States via Babb International, offers technical advice that is worth checking out. Links: Babb Lumber Company, AerBlock and Sider-Oxydro.
David Pearson is an architect and author based in the United Kingdom. His books include The New Natural House Book (Fireside, 1998) and New Organic Architecture (University of California Press, 2001). He is founder of the Ecological Design Association and former editor of EcoDesign magazine.