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Building with AAC has many advantages. Aerated Concrete is a highly cost effective, durable and sustainable material with high thermal and acoustical insulation properties.

AAC is made as a precast building block of various sizes and shapes from panels to blocks to structurally reinforced panels for floors and roofs. Panels are usually 24" wide, with thicknesses between 8" and 12" and lengths up to 20 ft. Blocks come in either 24", 32" or 48" lengths, are between 4" and 16" thick and 8" high.

Building Block                                                    U-Channel

     © Create Green Home

AAC creates a house envelope with no thermal bridging, (common in wood framing technique) and since AAC modules have high thermal mass inertia and are airtight, they provide a highly thermally efficient home.

Having high thermal mass means that blocks have a capacity to absorb and release energy slowly over time. It is a very important element for providing high indoor living comfort because it prevents rapid temperature swings caused by extreme daily outdoor temperatures and eliminates constant cycling of the heating or cooling system to maintain the preset temperature.

AAC modules feature an R-value of approximately 1.25 per inch but exact R values vary by thickness and geographical location of construction. From my research I found out that there are tables that illustrate what Equivalent R-Values would be for different thicknesses of the AAC block and the geographic location where they are being installed. This data is compiled by AACPA (Autoclaved Aerated Concrete Products Association). Refer to their site for more information. For example, a 10" AAC installed in Denver provides an Equivalent R Value of 20.16.

Measure of material's heat-conducting properties: Heat conduction rate per unit surface area per unit temperature difference between its two sides.

How do I convert U-Value from SI units to English units?

Divide the SI number by 5.678. For example, If U=1.4 W/m²K in SI units, then 1.4/5.678 = 0.246 Btu/hr-sf-°F in English units.

Conversely to convert from English to SI, multiply by 5.678:  0.246*5.678 = 1.4 W/m²K.

What is R-Value?

R = 1/U-Value

A measure of the capacity of a material, such as insulation, to impede heat flow, with increasing values indicating a greater capacity

AAC also improves indoor air quality because it is an inorganic material which does not off-gas any toxic fumes, contains no toxic materials and does not decompose over time. In addition to being recyclable, it is also non-combustible, mold and pest resistant material.

AAC is manufactured from all natural materials. The main ingredients are Portland cement that is mixed with lime, silica sand (or recycled fly ash - byproduct of coal burning plants), water and aluminum powder and poured into a mold. After a while, aluminum powder starts to react with calcium hydroxide and water in the mix to create hydrogen. Hydrogen gas causes the mixture to foam and expand its original mass to roughly twice the volume. Hydrogen eventually escapes into the atmosphere and is replaced by air in the already formed cavities. The material is then removed from the molds and while still being soft, is cut into blocks and panels and sent to autoclave chamber for 12 hours to cure. Under high temperature and steam pressure the material cures into AAC ready to use on the construction site.

Installation is rather simple but it may require use of light cranes to assist the crew in positioning the larger or reinforced panels. Blocks can be positioned by hand since they are very light, composed of about 80% air.

Lintel

Wall Unit

© Create Green Home

Material can be easily manipulated by the building crew using normal hand tools to cut, drill, nail, groove, route, screw into, sculpt and further shape this flexible material to accommodate various home designs.

In terms of cost, I found different estimates but they point to an 8"x8"x24" block costing about $3 or $2.30 per sqft which is comparable to the conventional Concrete Masonry Units (CMUs).

For installation, it is much lighter then CMUs, and has better insulating properties which will result in lower energy bills over time. It is also highly durable. It does not decompose, warp, rot, rust and requires very low maintenance.

Houses built with AAC can be easily finished on the inside with either paint, tile, plaster or gypsum boards or even left untreated. The outside walls can be treated with stucco or cladding materials such as vinyl, wood, or cement boards.

There are currently few manufacturers in the States. One is Xella Aircrete North America (German company) with offices and factories in Georgia. The brand name they sell here in the US since 2006 is a product called Hebel AAC. Xella also has another brand name, YTONG that they sell in Europe and other parts of the world.

Another company here in the US is Safecrete in Georgia and Aercon in Florida. You can visit their informative websites to learn about particular AAC products they offer and see actual residential and commercial projects.

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