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Sustainable Building Blocks

 Lighter than concrete, these blocks also have much better insulating qualities.

WHEN MR. WILSON approached Rob Smith, president of e2 Homes, about building a water-efficient, net-zero energy home with no drywall or wood on the first floor for one-third less than another builder’s bid, e2 Homes rose to the challenge. The 4,300-square-foot home incorporates Aercon aerated autoclaved concrete (AAC) blocks, which provide both structure and insulation.

AAC Blocks at a Glance

Pros:

  • More fire resistant, lighter (50 percent lighter than clay blocks of the same size), and better insulator than conventional cement.
  • Durable.
  • Insect and rot resistant.
  • Sturdy; structures can be designed for earthquake- and hurricane-resistance.
  • Insulating and soundproofing qualities.
  • Recyclable and less material-intensive than conventional cement, using 50 percent less energy.
  • Simultaneously provide structure and insulation, with low maintenance costs.
  • R-value for 8-inch Aercon wall is 11.5, but with a greater thermal mass than for a stick frame home.
  • Non-allergenic material results in high indoor air quality; can be finished with non-toxic plaster and stucco.

Cons:

  • Blocks may contain fly ash, a by-product of coal combustion that is not always tested regularly for toxic contamination.
  • Most American contractors are unfamiliar with the product, and so require training.
  • There are few AAC block manufacturers in the United States, which boosts the cost of the product.

AAC blocks are composed of water, sand and lime and contain air bubbles, which boost the insulative properties. Chemical reactions with gases make AAC blocks lighter, yet more insulated and fire resistant than concrete. This material eliminates the need for drywall and wood; it also prevents moisture issues in the humid climate of Florida.

e2 Homes hired a consultant to train its masons in the AAC block construction process. The 8- and 12-inch-thick walls are reinforced using standard rebar with core blocks, or a Go-Bolt system is cast into the concrete slab. Roughly one bag of thin-bed mortar is used per half pallet of block. Precision cuts for window openings are made with a band saw, and cores can be drilled as needed, which can be used for plumbing lines. Handholds and damage are repaired using patch.

The AAC blocks deliver both energy efficiency and thermal mass and create an airtight building envelope. The home has a supply-only ventilation system and high-efficiency air-source heat pumps. The energy efficiency of the home allowed the HVAC system to be downsized by 30 percent. AAC blocks are also mold resistant, an appealing attribute for Mr. Wilson, who wanted to avoid moisture issues in the hot, humid climate where he lives.

As a residential construction firm specializing in custom luxury homes throughout Central Florida, e2 Homes brings a thoughtful and flexible approach to green building. e2 is experienced in green certification programs, and roughly half of its clients wish to pursue LEED certification for their projects.


Sarah Lozanova is a green copywriter and communications professional and an adjunct instructor for Unity College and a regular contributor to environmental and energy publications and websites, including Mother Earth Living, Earth911, Home Power, Triple Pundit, CleanTechnica, the Ecologist, GreenBiz, Renewable Energy World, Windpower Engineering & Development, and Solar Today.