AAC: Autoclaved Aerated Concrete

Some call Autoclaved Aerated Concrete (AAC) a near-perfect building material. Patented in 1924 by a Swedish architect, AAC is made of common ingredients: portland cement, lime, silica sand or fly ash, water and a dash of aluminum powder. The material is acoustically insulating, energy conserving, resistant to fire, decay and termites, and can be cut with a handsaw and sculpted into architectural details. Europeans have built a million houses and buildings with AACAAC’s cellular spaces make for excellent insulation. Hebel’s calculations indicate that an 8-inch AAC wall has an R-value of 11 but, because of reduced air infiltration and increased thermal mass, it outperforms a stud wall rated at R-30. “You get a flywheel effect from its mass—reduced temperature fluctuation, because it’s slow to heat or cool. Hebel says its walls are two and a half times more airtight than standard wood frames or concrete blocks. One of the few Arkansas homes built almost entirely of AAC block is located in Pea Ridge, Arkansas and can be toured with an appointment. It i