Autoclaved Aerated Concrete

Autoclaved aerated concrete (AAC) is an interesting new addition to the palette of building materials available in the northeast.  It has advantages over CMU in some criteria, and advantages over stud walls in others.  But AAC does come with limitations in other areas that need to be understood during design.  Below is a list of advantages and disadvantages of the product:

Advantages:
Light weight vs. CMU Larger module size (faster installation) Available in typical masonry wythes (4”, 6”, 8”, 10”, 12”)
Masonry coursing/bearing requirements reduced
Continuous insulating value – eliminates thermal ‘short-circuiting’ Air barrier potential
Vapor permeable – vapor barrier may not be needed in some wall applications
Conduit and wiring can be run in chases routed into material surface
High fire ratings
High sound attenuation
Zero-waste manufacturing
Approx. 1% on-site waste generated
Available in large and custom sizes
No off-gassing/VOCs
Can be shaped/sculptured
Can be cut with woodworking tools
Simplified detailing
Opportunity for overall project cost savings
LEED-friendly

Disadvantages:
Interior finish required (2-coat plaster or furred out)
Residual moisture in product – must ‘breathe’ after installation
Reduced load-bearing capacity
Lack of experienced installers
Brittle material (offset somewhat by solid block units)
Tendency to chip and wear at edges if left exposed
Only one supplier for Northeast (others exist)
Lack of familiarity among owners and industry

Applications:
Likely applications in this region include interior partitions where sound separation, fire separation, and abuse resistance are important.  It also has good potential for exterior backup walls in cavity wall construction within steel frame buildings.  This product could also see use in load-bearing masonry wall systems for buildings of two-four stories that utilize pre-cast concrete plank flooring systems.  The product will be beneficial for several LEED point categories if the need arises on a project.  It is also useful where high fire ratings are required in shafts, fireproofing, and rated enclosures.  At HKT, it could find use in schools, public safety (jail cells and apparatus bays), and in additions to existing buildings using cavity wall construction.

Caveats:
The product is not new to the construction industry but it is new in this region, so finding qualified installers that are price-competitive could be challenging for the short term (I think this is due more to perception than reality).  Also the product properties are different than CMU so detailing, coatings, and finishes need to be reviewed carefully for compatibility.  Owner opposition to using a “new” product could also limit applicability.

AGB 5/2005