Some products help us use other products or materials more efficiently. For example, drywall clips allow the elimination of corner studs, engineered stair stringers reduce lumber waste, and concrete pigments and polishing systems can turn concrete slabs into attractive finished floors. We also recognize some products, like vacuum plumbing systems, which use less material than their conventional counterparts. Many products with this attribute are fairly unique, so we bring a skeptical eye to manufacturer claims, but not a specific standard.
Before specifying efficient heating and cooling equipment, it’s important to do what we can to reduce heating and cooling loads. Insulation is one of the key products to consider here, but because there are so many insulation products on the market, we look for additional benefits. Examples include cellulose insulation with recycled content, mineral wool insulation with no flame retardants, and fiberglass insulation with no formaldehyde binders. Other products in this area are high-performance windows and glazings, products that contribute to building airtight envelopes, products that reduce thermal bridging, and window-retrofit products.
With products in this area under constant development, we are always refining our approach. For example, as we have learned about insulation products with hazardous flame retardants and blowing agents that have high global warming potential, we have removed those products from GreenSpec, pending manufacturing changes. We encourage building professionals to pressure manufacturers for those changes through specification language and purchasing decisions.
Aercon manufactures autoclaved aerated concrete (AAC) for wall, floor, and roof applications at its plant in Florida. An 8" Aercon wall achieves R-11.5, or R-1.44/in. Like other AAC products, Aercon AAC is fire-rated to four hours. It is 70%–75% sand, 10%–15% portland cement, with the remaining ingredients being lime, anhydrite, and slag.
Commercial production of autoclaved aerated concrete (AAC) began in 1930 in Europe, where it has been widely used for decades. Concrete masonry units (CMUs) made from AAC are lighter than conventional CMUs, generally have no cores, and provide higher insulation levels than CMUs, with R-values of up to 1.25 per inch. While that R-value is an order of magnitude higher than standard concrete, it’s much lower than conventional foam or fiber insulation materials, so additional insulation remains necessary in most North American climates.
AAC’s lighter weight means that fuel use from transportation is decreased—but with few manufacturers in North America, this advantage disappears the farther you have to truck it. It has about 20% of the density of regular concrete, greatly reducing the amount of portland cement used while simultaneously increasing thermal performance. This makes AAC an attractive alternative to conventional concrete, although other materials, such as insulated concrete forms, may be superior to either depending on the application.
AAC has only about 10% of the compressive strength of conventional concrete; manufacturers may increase the product’s strength by including reinforcing steel rods or mesh. Structural applications of unreinforced AAC are limited to low-rise buildings; in high-rise buildings it may be used in partition and curtain walls. AAC has very good sound-absorbing characteristics and can be used as a firebreak. Because AAC is a porous material, it must be protected from moisture with claddings or coatings.
AAC is not is not installed in the same way as conventional CMUs; greater care must be taken in installation because the shallow mortar bed does not allow for alignment adjustments easily made with the deeper mortar beds of conventional CMUs.
For more information on AAC, see Autoclaved Aerated Concrete (AAC): Will the U.S. Ever Lighten Up? in our blog.
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