PATH - A Public Private Partnership for Advancing Housing Technology
PATH Case Study
Better Building Blocks Make Better Homes
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[IMAGE: Steel rebar reinforces AAC block to create durable walls that easily meet load requirements.]
"On the Foster's residence, we used 10" AAC block to create an exterior wall with a performance R-27 value and we used cellulose insulation to create a ceiling with an R-40 value. The performance R-value of an AAC block wall depends on the kind of block used and its geographic area."
For the impact of geographic and block type variables on the performance R-value of an AAC wall, visit TruStone America at www.e-crete.com: Chapter 3, page 8 of the technical design manual under "Engineering."
"AAC block provides for walls that are very straight and consistent from an insulating and smoothness perspective. There is less thermal bridging than with wood framing, and you don't have to deal with batt insulation on the walls. When you put your hand on the exterior wall, there is hardly a difference in temperature from the interior wall. All of our customers speak of the unbelievable difference in comfort and energy savings associated with AAC."
According to Oak Ridge National Laboratory, energy demands of a home with AAC walls are about 18 percent less than wood-frame walls, 36 percent less than two-core CMU, and 23 percent less than steel stud walls.
INSTALLATION AND TRAINING
"Originally, we were hoping our regular masonry crews would be interested in building with AAC, but their unfamiliarity with the product drove the price up more than we expected. Being hands-on contractors who design and build, we invested in our own AAC crew."
"At first, we had to work closely with the crew to get them used to the different processes, but it's not that different. Masonry crews have to adjust to using a special polymer-modified thin set mortar system, which creates less margin for error. Our masons use a special notched trowel to apply the thin set mortar and create texture for subsequent pieces of block."
AUTOCLAVED AERATED CONCRETE
AAC is an economical precast, manufactured building block made of all-natural raw materials. AAC is available in a variety of forms, ranging from wall and roof panels to blocks and lintels. It is fire- and termite-resistant, and is lighter and easier to cut than conventional CMU block. AAC also has superior thermal and sound insulating properties. AAC can be sawed, drilled, nailed and milled, making it highly adaptable to a variety of architectural styles.
"AAC blocks can either be installed directly on a foundation system or on an elevated floor for multi-level construction. As with typical masonry projects, the initial bed joint is critical because the base mortar joint must be level and true to avoid continual adjustments. Initial bed joints are usually between 3/8" and ½" thick. Using a waterproof mortar on the floor slab under the first course of block protects the building from water in the soil. A horizontal moisture barrier in the first mortar joint is another way to protect against water intrusion."
"Depending on the architectural style, we build the exterior walls with the AAC block and attach the trusses using a top plate, anchor, or ledgers consistent with typical construction methods. Ledgers are attached to J-bolts that are installed to the bond beam block with 4" concrete around the anchor bolt filled to the face of the wall."
"AAC blocks can be cut with a handsaw and sculpted with a rasp, creating endless design possibilities. At first, we purchased a big band saw thinking we would have one table to do all the cutting, but it turned out that the laborer working next to the mason can actually handsaw cut the pieces right on the spot rather than having to travel all the way over to the sawcutter and bring the piece back. With handsaws, we were able to cut the blocks right on the scaffolding and put them in place twice as fast as having a central sawcutter. The handsaws are not typical handsaws though. They are 3 feet long, ¼" carbide-tipped handsaws. Other masonry tools we use include sanding floats, rubber mallets, and levels. The AAC waste created on-site can be recycled or disposed of in a regular waste bin."
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Content updated on 9/5/2006
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