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Is AAC expensive?A simple question hiding a million variables. Let’s say you want to build a typical house with it. You’ll need strength class AAC4 and 8x8x24” blocks. You can use panels, but those will be more expensive, so let’s consider blocks. A solid 8x8x24” braac is currently selling for $6.98 from Aercon (6May2020). That’s $5.24/sq ft. A typical concrete block (CMU) from a box store nearby is selling for $2.07, or $2.32/sq ft. How does that $2.92 price affect your build? If it takes 1,800 braac to build your house, then they’ll cost $5,256 more than if you made your house with CMUs. Is that a lot? Some people spend more than that on curtains; has the cost added value? Also, consider the CMUs are going to need much, much more rebar, concrete, and mortar. CMUs will need a stronger foundation and are heavier to move. To compare AAC to wood framing (often quoted around $3/sa ft), consider materials & labor for: lumber framing, insulation to a comparable R-value, sheathing, tape & nails, cladding or brick, sheetrock, paint, increased costs for openings and the extra costs to plumbers and electricians having to work through studs. Are you over $5.24/sq ft yet? CMUs also need many of the things listed for wood framed walls, AAC walls need only plaster and stucco. You can add more to an AAC wall, but whether AAC is comparatively expensive depends on what you’re comparing it to.
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What are the advantages and disadvantages of AAC?Below this FAQ section is a "complete" list of advantages and disadvantages, culled from various sources and personal experiences. If it appears something has been left out or is incorrect, please contact us or post in the forum topic "Advantages/Disadvantages List."
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What type of mortar is used for the first course of an AAC wall?Check with your structural engineer and local building codes. In many instances, Type S will be recommended.
The Complete Advantages / Disadvantages List
DURABILITY
FIRE
PROJECTILES
WIND
EARTH
ANIMALS
PLANTS
FLOOD
WATER & VAPOR
ENERGY
LIGHT
HEAT
MASS
ENVIRONMENT
CARBON
LIFE-CYCLE
ECOSYSTEMS
TOXICITY
CLEAN
SOUND
COMFORT
WORKABILITY
INSTALLATION
SPEED
SUPPLY
QUALITY
COST
EXPERTISE
FAMILIARITY
Advantages
Blue text is for a perceived advantage that really isn’t an advantage. Perhaps because it’s relatively newer (wood, concrete, rock, brick and dirt have all been used much longer), there is a natural skepticism and advantages that are solely perception-based are rare.
With the right foundation and minimal maintenance, AAC structures could last hundreds, if not thousands, of years, as other rock and concrete structures have. However, it was invented only 100 years ago, so this is not verified by actual experience.
Noncombustible and virtually fire proof. Superior even to concrete & ICF walls which lose structural integrity in high, sustained heat; however, if AAC is on a concrete foundation, this will be irrelevant.
AAC is bullet-resistant. The US Army uses a similar material, SACON, to trap munitions.
“[AAC] structures are prepared to meet 150 miles per hour (mph) winds (Category 4), and with proper reinforcement, can be engineered to withstand winds of 200 mph or more (Category 5).” (1)
Pest resistant. Insects, rodents, and other animals do not eat or burrow in AAC.
Plants and fungus do not eat AAC. Thus, it is mold resistant and not susceptible to decay like biological materials such as lumber.
“AAC homes are not destroyed by floods, either: they resist rising waters, rot, mold, and mildew and can be cleaned, repainted, and reopened [with] no rebuilding necessary.” (3)
Water-tight. Although AAC will absorb its weight in water, it ultimately floats. The spherical bubble structure blocks water from penetrating through the AAC. Blocks have been exposed to weather in temperate zones for decades with no degradation. It is a vapor barrier.
The bare material is very white. It reflects light and heat away from the building.
AAC entraps air in relatively self-contained bubbles & not the capillaries in traditional concrete. The bubbles provide improved resistance to heat transference (“R-”) in a strong, rock-like material. AAC has superior R- value compared to traditional concrete (poured or block): without remdiation, concrete walls typically range from R0.8 to R1.1 while AAC is closer to R11. However, all concrete methods supply thermal mass and air-tightness that improves thermal performance. An 8” AAC wall is comparable to a framed wall of R-15 to R-30. (units are imperial)
The increased air in AAC means AAC is light.
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Cheaper to transport & move (and lower carbon footprint) compared to concrete & concrete block
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Easier for installers to lift
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The foundation doesn’t have to be as strong as for other concrete buildings, resulting in less money, labor, and materials
Compared to a traditional concrete house, AAC uses much less concrete and has a much smaller carbon footprint. Concretes that absorb CO2 are in development but are not in wide use in residential structures and are not carbon neutral in their life cycle.
The energy efficiency and air-tightness of the building envelope (in air-change/hour or ACH) of AAC results in less energy to heat or cool: cost savings for the owner and lower greenhouse gas emissions for the environment.
AAC is completely recyclable.
Quarry of AAC materials has a smaller impact on ecosystems than forestry management practices. Compared to wood frame homes, AAC allows forest carbon sinks and their ecosystems to remain intact.
AAC is hypoallergenic and free of toxins and VOCs. The most concerning component is aluminum, and there is more aluminum in the dirt under your feet than in an AAC block.
Insects, rodents and other pests have no place within the solid, seamless walls to hide, grow, or transit.
Acoustic performance of AAC walls is favorable. The lack of air penetration and the mass and rigidity prevent external sounds from entering the building envelope. STC = 45 for 8” thickness.
AAC is hygroscopic, so human skin within the building will experience a more comfortable and natural-feeling structure (similar to wood).
The bubble structure makes AAC easy to cut,”shave, and shape, accept nails and screws readily,” (4)
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Easier install of electrical and smaller-diameter plumbing chases (can be routed and plastered over), which remain in the inside envelope of the structure.
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This gives it design and construction flexibility: Decorative shapes, rounded edges, customized sills and trims, etc. are possible and simple to create.
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Can easily make adjustments at the build site
Supply is predictable and predicated on factory capacity.
The block is consistent from batch to batch. It is precision cut to a near exact size, aiding design & installation.
Amenable to do-it-yourself (DIY) builders. Not conceptually difficult for crews to learn.
AAC is one of the newer building materials and is innovative. This should not lead to irrational exuberance; like any material, AAC has both advantages and disadvantages. Researching them, such as on this site, is recommended.
Disadvantages
Red text is a perceived disadvantage - one that doesn’t appreciably impact the use of AAC as a building material. But since perception has an appreciable impact on acceptance of AAC, it’s included as a disadvantage, whether or not the perception is naive.
In a culture of planned obsolescence and rapid change, permanence may be a disadvantage. However, it is much easier to modify than "solid" concrete structures and permanence is only a disadvantage when compared to methods that engineered for rapid recycling.
Protect from a grass trimmer (can be gouged).
AAC can absorb its weight in water if submerged, and is heavier to move when wet. Wet AAC may prematurely dull blades used in cutting or drilling; however, dust is then minimized.
The bare material is very white. It reflects light and heat away from the building
AAC is filled with air in relatively self-contained bubbles, rather than the capillaries in traditional concrete. Hitting the AAC results in a hollow sound. This has no disadvantage other than the perception that the material isn’t “solid.” Solid is usually perceived as superior, but solid thermal conductors are undesirable if thermal resistance is preferred.
AAC has a lower compressive strength than traditional concrete and even some fiber-reinforced non-autoclaved aerated concrete. This is like saying a plane that can fly around the world without landing is terrible because it can only do it once. The strength of AAC is far superior to lumber - a material instinctively trusted - and is more than strong enough for all residential applications.
As a concrete product, there is more CO2 emitted in AAC creation and shipping than wood, which is a temporary carbon sink. AAC also uses significantly more water during construction than wood, steel, or other building methods (e.g., straw bale, rammed earth).
Like all cut and shaved concrete products, the silica dust is dangerous and should not be inhaled. This disadvantage is limited to when AAC is being cut or shaved and is not a concern for installed AAC.
The mass and rigidity reflect sounds generated within the building envelope.
The material is brittle at the edges and can chip. It is not a significant disadvantage:
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Chips have a small, probably unmeasurable, effect on the insulative properties if the chip is large enough and replaced with a less-insulative material like block patch or stucco.
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Filled chips marginally increase materials cost & install time.
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It has an aesthetic impact that is unimportant since the block will be covered, but significantly impacts perception of block strength among customers and builders.
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It has no structural impact unless very large, in that case it could lead to waste. Chips of this size may occur during shipping, typically less than 2%, and are unlikely to occur on site.
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Chips should not have an impact on installation unless the installer spends time “choosing” blocks for particular areas; this should be unnecessary
The bubble structure, being easier to work, has less shear strength for holding fasteners, so specific fasteners are required.
Hairline cracks in the block may manifest as larger cracks later; careful observation (10 - 15 seconds per block) is needed to ensure blocks with hairline cracks aren’t installed. Also, these cracks contribute to waste.
There are few factories producing AAC, limiting supply, and they may be distant from the build site, requiring extensive transport.
Manufacturers sell by the delivery truck, and within a truck, by the whole pallet. Careful estimation is required, followed by intentional over-estimation to prevent waste. Excess usable blocks are likely, increasing cost. This is less likely with panels. Depending on your purchase quantity, manufacturers may be of limited assistance in estimating.
Fewer architects, engineers, and contractors are familiar with AAC. Inexperienced crews are more prone to mistakes and a slower pace; experienced crews may be locally unavailable or have to travel. Resources for crews & DIY projects are more often on-line.
The name “AAC” is cumbersome. There are multiple names for AAC and many items (not building materials) also called AAC. This impedes communication, SEO, marketing, consumer awareness and acceptance.
Earthquake resistance of AAC is an active area of research. There are indications that AAC performs as well or better than concrete in seismic zones, dependent upon variables such as number of openings, geometric structure of the building, AAC to reinforcement ratio, etc. “The results of AAC building seismic analyses point out that for 1-2 storey buildings and for low to medium levels of excitation (for rock sites),” the AAC failure state may not occur. Also, “the very low weight of this material and its high deformability (low value of Young modulus in compression) tends to reduce inertia forces on the building induced by the seismic motion.” (2) However, wood and steel are generally preferred for seismic zones.
Anecdotally, AAC might result in a slower build; others claim it is as fast or faster. Variables to consider are the experience of the crew in both building techniques, averaging the effects of weather, the percent of wall (and/or floor, ceiling) using AAC relative to the compared method, the width of the AAC block, the level of flexibility in the building plans to accommodate each method, etc. The author is not aware of a robust, evidence-based, peer-reviewed comparison of building techniques, although it's faster than brick, according to this YouTube video.
Fluctuating market rates for building materials prevent an enduring analysis. CMU (concrete block) is a good proxy comparison because raw materials are similar. AAC blocks can be double the price of CMU per unit, but CMU will require consideration of freight (weight), extra rebar, mortar, concrete reinforcement, foundation reinforcement (and expansion for interior wall finishes), labor for running services in walls, gypsum board, insulation to obtain R-value parity, etc. Profitable U.S. builders are using AAC and have provided the author with various estimates between less than the cost of typical materials to as high as 10% more. YMMV. Also, while some new tools will be required (disadvantage), they are not prohibitively expensive (advantage). Some can be made by a knowledgeable crew.