Blog Post

Autoclaved Aerated Concrete (AAC): Will the U.S. Ever Lighten Up?

Lighter, more fire-resistant, and a better insulator, autoclaved aerated concrete caught on in the rest of the world ages ago. It's taking a lot longer in the U.S.

The porous AAC structure comes from being "leavened" with aluminum. Photo: H+H UK

To read what manufacturers and distributors say about it, you'd think autoclaved aerated concrete (AAC) was some kind of new, space-age environmental miracle.

Although it certainly has some nifty properties, AAC isn't new and isn't miraculous--but it's certainly popular in Europe, and has been for decades; according to one source, it accounted for 60% of all new construction in Germany in 2006. It has enjoyed pretty flat market share (of near zero) here in the U.S., though, since it was first introduced in the 1990s.

Is there space for AAC in the U.S. market? Should the green building community be working to make space?

How AAC is made

AAC is similar to other concrete types, except that it contains no aggregate; sand or fly ash is included, with aluminum powder added to react with one of these ingredients and "leaven" the concrete, creating tiny bubbles just like baking soda does when it reacts with the buttermilk in your muffin batter. (Your muffins are full of carbon dioxide bubbles, but AAC is full of hydrogen bubbles.)

[Note: Robert Riversong points out in comments that sand is aggregate, which I also thought when I started researching it, but after some more digging, my understanding is that the sand is used as a reactant and is therefore not considered aggregate in AAC. For more, see here.]

The concrete is poured into molds, left to rise, and then "baked" in an autoclave, which uses steam and pressure to complete the chemical reactions and speed up the curing process significantly--completing in hours rather than weeks. The resulting blocks are so full of bubbles that a block of the same size has about one-fifth the material required by regular concrete.

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Like conventional concrete masonry units, AAC is sold in a variety of block shapes and sizes, but unlike conventional units, most don't have cores. They are porous and light, like muffins, but not hollow.

Benefits of AAC

The main advantage of AAC when it was first developed in Sweden in the early 20th century was simple: it wasn't wood. It's still not wood, but in North America (unlike in Sweden at the time and in most of Europe now), wood is still plentiful and cheap.

Compared with conventional concrete, AAC still has advantages, though:

  • It uses less material--important for concrete, since portland cement is one of the most energy- and carbon-intensive building materials.
  • Despite the energy-intensive autoclaving process, manufacturers say it takes about 50% less energy to make, because of the lower portland cement content by volume (we're haven't found anyone to challenge those claims, but are still looking for data).
  • It's lighter, which cuts down on transportation costs and fuel use.
  • It's a better insulator, with a steady-state R-value just a hair above R-1 as opposed to something more like R-0.2 (neither of these factors in thermal mass, which we'll get to later).
  • Air leakage is minimal.
  • AAC also has excellent soundproofing properties.
  • It can also be used as a firebreak.

Drawbacks of AAC

In a report written for UC–Davis (PDF), Stefan Schnitzler finds few disadvantages to AAC. Here are the two demerits on his list:

  • There are few manufacturers in the U.S. (that was in 2006, and now there are almost none, since Xella has moved its Hebel operation to Mexico); this means higher costs, which is a huge barrier for adoption.
  • AAC requires a learning curve for builders, because the mortar application is more precise.

We would like to add a few drawbacks that we've found:

  • The barriers for builders don't stop with the mortar. According to Derek Taylor, owner of AAC distributor SafeCrete, the only manufacturer in North America right now is a German company whose block dimensions don't work for U.S. builders. These often need to be sawed, adding labor and fuss to a building system that's supposed to be simple. (Taylor's looking forward to two new plants coming online in the States in the next couple years.)
  • Since right now your AAC is most likely coming from Mexico, the advantages offered by lighter weight will diminish significantly as the mileage increases.
  • Thermal properties are better than those of conventional concrete, but they aren't good enough to make AAC a viable wall material (relative to BuildingGreen-recommended R-values) in most U.S. and Canadian climates without additional insulation. (The European climate, where AAC is popular, is milder.)
  • Unless rebar is added--which adds to the weight and amount of material in the blocks--AAC can only be used for low- and mid-rise construction. But it seems to be popular for single-family homes as well as schools.
  • Unlike conventional concrete, AAC can't be used as a finish; it is more porous and needs cladding or stucco on the outside so it won't absorb moisture.
AAC is popular for residential construction but not suitable for high-rise buildings without structural reinforcement. Photo: SafeCrete

Would you use AAC?

That said, AAC does appear to have significant advantages for applications where conventional concrete would normally be the best material--like in the American Southwest and in other climates where thermal mass can increase the "effective" or "mass-enhanced" R-value of the wall. Even then, its performance may still be outmatched by that of insulated concrete forms, depending on the needs of the client.

Unfortunately, much of the information we have on AAC performance in the U.S. comes from manufacturers. We'd like to hear some empirical evidence from the field.

Are you using AAC on any of your projects?

If you've used it, how did it perform? If not, what would it take for you to try it out?

Published February 1, 2012

(2012, February 1). Autoclaved Aerated Concrete (AAC): Will the U.S. Ever Lighten Up?. Retrieved from https://www.buildinggreen.com/news-article/autoclaved-aerated-concrete-aac-will-us-ever-lighten

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Comments

August 4, 2020 - 10:53 am

Actually its perfectly rated, and you misinterpreted your own facts.

First, all concrete is porous, no matter the percentage of cement used. Even pure cement is porous. However, how porous something is does not measure permeability, but rather the extent of ingress on the exposed parts of the material. This means you don't want water to get on it and freeze because it will slowly crack pieces off. The pores on most CMU are larger than AAC creating more voids for water to collect. However, this does not mean that AAC is permeable. It is not. AAC is made up of closed bubbles that formed inside. More like closed cell foam - you know that foam they use in pools that doesn't feel right because it doesn't act like a sponge? It is, by itself, able to be made 100% airtight. Under presure, it is water permeable. So you need to seal it. Not a big deal. Please note that it is water permeable under pressure. water on it will find a way through it through gravity, but water thrown against it does not get sucked up like a sponge, neither by moisture in the air, because air-pressure is constant in all directions, and the relative pressure is not different in the AAC. As for the thermal mass, it is not as massive as a lot of other materials. However, it is a naturally non-bridging material. Ordinary Concrete is a thermal bridge. Note the statement "consistently cold" as it nullifies your assertion of thermal mass and AAC. Thermal mass is beneficial where the outside temperature fluxuates drastically. Like where evenings are in the 40s -50's or lower and days are in the 80's-90's or higher. Thermal mass is not insulation, it only absorbs and delays the transfer of energy across it. If the temperatures are consistently cold . . . or even consistently hot, thermal mass is not particularly useful anyway. In Minnesota winter you cannot afford to heat a concrete building without significant internal insualtion. In the Carribean, concrete buildings are often not fully enclosed because otherwise the building acts as an oven at night. It's always in the areas where tempertures vary consistently where thermal mass keeps you nicely at average. 

August 4, 2020 - 10:31 am

You can use any blade or tool you would use on wood. Only downside is that the AAC is more abrasive so you will dull the blades quicker. The AAC usually does not actually mind you using dull blades, even so the wood will. The aeration seems to make tearout a non-issue. You can use a router on it as well. I typically have a set of blades/etc. designated just for AAC so I don't mess up wood working projects with a dull blade by accident. Same tools though. 

August 4, 2020 - 10:19 am

Everyone I talk to seems to think that the main reason that AAC has taken off is that it is a great insulater. In actuality it is not. It is ok, but nothing truly exceptional. This is not the interesting part of AAC. AAC's magic comes from air-tightness, pest resistance, longevity, Ease of use, insulatability, and speed. After this I won't even mention fire resistance. All of this in one material. I'll start with pest resistance, because it is my personal favorite and why I intend to use it.

Pest-resistance: Roaches and other insects cannot eat it, get through it, build nests in it, or travel inside the walls of it. Termites could not care less for it. Rats, mice and other rodents do not chew it to shorten their teeth. As most people who have experienced a pest problem the problem is not the ones you see, its the ones in the walls that make more. A properly built AAC building is almost airtight (and actually airtight if you want to) out of a material pests cannot or will not use for their nesting or travel. If you build an appartment building out of this stuff it can prevent cross contamination of pests like roaches which love to use walls for their nests, but the fact that the walls have minimal voids means that pests have few places to hide, and extermination actions are highly effective. This alone makes this material especially interesting in areas with high pest problems such as Florida, Georgia, Alabama, Louisiana and some of Texas. 

Air-tightness and Insulatability: The number one factor for insulation is not R value, it is airtightness. Its why ultra high standards for efficiency like Passiv Haus require near complete airtightness and look at houses with infrared to find air leaks. These houses require a air exchange system or they are too airtight for people to live there. Most houses (especially in the states) are hilariously porus. It doesn't matter if you have R45 if you leave all the doors and windows open. That is AAC's special ability. AAC when used properly (not in any special way, just its normal use) results in a nearly air-tight building by default. This results in retention. Its smooth walls makes it highly insulatable without thermal bridges as well. It is for this reason that a lot of Passiv haus buildings are out of AAC. I was in a passiv haus in germany in the middle of winter once and had a candle lit for ambiance. After an hour or so the room was way too hot, and it was a sizable room. So the material is not what makes it special in insulation, but the ease of insulating the material. 

Longevity: Most of the rest of the world does not consider a 200 year old house to be old. A 200 year old house is considered normal age, even amoung wood constructions. 'Old' buildings are significantly older than that, some going back 500 or more years. US houses are old at 50 years, and practically ancient at 100. AAC was designed to replace the wood construction of Europe. It is expected to last more than 200 years when constructed properly with minimal maintenance. If you are worried about the energy used to make the building please note that you will never be able to make up the energy cost of building the house twice out of wood inside of a 150 year time period. A building that takes 150% more energy to produce still takes less energy if over its lifespan you would need to build an ordinary building over again. 

Ease of Use and speed: In the United States, builders are not familiar with this material. It takes them way longer to build with it than it should. Regulatory bodies do not know what to do with it, and architects are unfamiliar with it. That really does not change its ease of use or speed characteristics. In Europe, it starts with plans from the architect, who does not only by block but whole prefabricated walls and floors with cutouts for windows, doors, and stairs. Properly experienced teams of 4-6 people construct an ordinary 2 story building in a month, start to finish incuding electrical and paint on the walls. They are so fast that there are special rules for inspections to make the whole process faster and cheaper. For builders who have experience AAC can be cut, tapped, routed, nailed, screwed, and anchored like ordinary wood or drywall. This is not as important to the second owner, but in construction most people use construction or bridge loans to finance construction. Since these loans have higher interest rates and less favorable terms than an ordinary mortgage, being done with construction inside of 6 months without paying any overtime can reduce the costs of construction by many thousands of dollars.

There are many other materials that actually do better than AAC in any one of these categories. Wattle and Daub houses when raised off the ground and kept dry last thousands of years, have low energy use and cost in construction, and can be very air-tight . But they are not pest resistant at all. The same goes for hay-bale construction. Wood construction is easy to work with, can be fast, but has no fire resistance and has pests like termites that eat it. The drywall that goes on it is fast for making walls but acts as a superhighway and hidingspot for pests. Concrete is airtight by default, but is harder to work with, and takes a lot more time because you cannot build the next section until the first has cured. It is pest resistant, but not against rodents who actually like chewing on it to sharpen and wear down their teeth. It is also solid and crystaline and transfers sound incredibly well. Brick lasts a long time but again, rodents like to chew it, and takes more man hours to construct. Its not typically a hiding spot for pests, but it is actually hard to insulate without leaving voids (which can become super highways. AAC is a jack of all trades and that is what makes it so good. 

May 12, 2020 - 1:11 pm

San Diego's building department was not familiar with AAC, and given California's high seismic standards, they were not inclined to approve my project. I had to find a structural engineer in California who was familiar with AAC. Ditto for title 24. This delayed my project for at least a few weeks. Once I had the structural and title 24 taken care of, the city was satisfied. I had no problem with the inspector. Her job was just to make sure that I built what was is on the approved plans. 

As I mentioned before, I was not able to find a masonry contractor willing to take the job because they didn't know how to bid it. Plus they would've needed to train their masons on the use of an unfamiliar material. And they would have to bear the liability if something when wrong.

The reason I wasn't disuaded from using AAC was because I was stubborn, inexperienced, and naive enough to think I could do it. And I paid all my workers by the hour. This turned out to be an expensive house. (Even the guy who introduced me to AAC and offered to build the house for me, changed his mind and urged me to build with conventional concrete block instead.)

Another problem I encountered: since the factory was 1500 miles away in another country, obtaining additional block would not be a simple matter. I couldn't simply call a local supplier and have additional block delivered the next day. So I had to either buy lots of extra block, or risk running out.

In conclusion, if I lived in an area where AAC is readily available, and where I could find masons who are familiar with AAC, I might use it again.

One last point, when calculating energy efficiency, you need to include the energy it takes to obtain the raw materials, the energy used in making the product, and the energy needed to transport it to the building site. 

May 12, 2020 - 6:21 am

I'd like to thank and congratulate Steve for the post and on trailblazing AAC construction in San Diego. Up until now I was only aware of one home in Alpine and one in  Ramona. I'd love to hear more about your experience getting the build permitted by the city. Thank you 

April 17, 2020 - 5:20 pm

I completed construction of my AAC house twelve years ago (2008). I'm happy with the house, but would I build another like it? 

The material was shipped to San Diego, CA from Monteray Mexico. Shipping cost as much as the material.

Building department was reluctant to approve the material. I had to find both a willing structural engineer and Title 24 consultant. 

There were no masonry contractors willing to take on the job in my area, so I had to hire my own masons. They made some blunders, which worry me to this day. If you choose to use AAC, make sure your masons are trained -- or train them yourself.          

Energy efficiency: Manufacturing involves baking at high tempuratures for many hours, which uses a lot of energy. Transporting by truck from central Mexico used a lot of fuel.      

Saving trees?: even though my exterior walls are AAC, the roof trusses, roofing sheathing, floor trusses, floor sheathing, and interior wall framing are all wood.

Electrical wiring requires that MC be imbedded in the walls, which is messy and more expensive

If I were to build another AAC house, I would use 10" or 12" wide block instead of 8". Since I live in a seismic zone, I'd opt for a higher density block for it's added strength. For drilling holes for rebar, I would use a hole saw instead of boring bit because it produces less dust. I'd order prefabricated AAC lintels which would save labor costs and give more consistance results. For grouting, I would would use pea-gravel concrete with a super plasticizer to improve flow and eliminate the need for vibrating.

So would I build another? Maybe. I do getting bragging rights for having built the first AAC house in San Diego. And it looks cool with the rounded corners (I usee a rounded rasp made for this.) But it was expensive. And I think I could have achieved better thermal efficiency with other mathods. 

December 13, 2019 - 12:38 pm

I think aac is the best material for individual construction. I myself am from Russia and here this material began to be used more often. With the advent of polyurethane adhesive, it is possible to build from aac even easier. If I have to move to the United States, I will build a house from aac with my own hands, I will insulate with Styrofoam and goodbye to the bills for heating and air conditioning))) I am interested in whether it is possible to buy aac in new York or new Jersey?

October 26, 2019 - 1:18 pm

I have a couple of small projects happening in a flood-prone area. And being European I've grown up building with ACC panes. Where is a good place to get hold of smaller quantities of 4" panels in the NYC area?

October 10, 2019 - 4:52 pm

since 3 years I'm studying the market but I'm not sure there is codes for lightweight block to build in California in general and I'm sure this kind of block more effective than wood and other regular stuff they use to build the houses in Sacramento or on the California in Jerome and more green then

if someone interested or support me with information that can help me to open medium business or small business manufacturing the AAC block or the CLC block which is the word lightweight concrete block different sizes. 

August 25, 2019 - 11:48 pm

Build a simple Box like a Mobile home Set up. 60 to 70ft Long and the standard With from 12 to 14 ft.

100 times sturdier than any Mobile Home or Manufactured Housing. Better Insulation, No termites.

But American Builders are about 100 years back.

Chris

May 29, 2019 - 7:07 am

Do you have any blueprints available using AAC available for sale?

February 28, 2019 - 4:19 pm

"The European climate, where AAC is popular, is milder."  Ever wonder why skiing is so popular in Northern Europe and parts of southern Europe? Because it gets COLD and ... snows! Just like the US, the climate is varied and goes from as cold as Canada to as warm as Florida. I've been in Portugal when the water mains froze and the South of France in winter when I was in shorts and shortsleeves. There is no "European climate" any more than there is a US climate. It varies region by region.

February 17, 2019 - 8:11 am

It's a great product with amazing properties that satisfy so many needs and concerns - in the proper applications.

I was on a team that coordinated all of the US standards testing and engineering design standards/details, designed and sold some fairly large projects with Ytong, Hebel and Contec Mexicana, acted as a site/design consultant for Hensel-Phelps on a design/build Defense contract, and a number of other industry initiatives.  It's a product that has it's applications - you have to know what those are to be cost and performance effective.  And in order to implement the product into a project, a single person needs to understand everything from conceptual building performance criteria, to design limitations and cost of erection/setting, to material logistics,staging and scheduling, all the way through to rendering and maintenance.   I worked with an incredible consulting engineer and together we worked with the materials for some truly unique and pioneering applications.

Good product.  Just know it's limitations and use it where it makes sense, and not just inject it where it's not the best product for the application.

j

November 5, 2018 - 1:52 pm

I live in Bryant, AL and we have built 2 AAC homes, sold them and are just now starting on the 3rd which we will retire in.  Neither of the homes we built had any insulation in the walls.  We used stucco on the outside and standard sheetrock  on the inside.  The first one was built in 2002, the second in 2006.  We have recently talked to the owners of both houses and they are very satisfied with the performance.  They say the utility bills are very low compared to other homes.

November 1, 2018 - 11:43 am

Cellular lightweight concrete (CLC) has insulating and strength properties and a density that is similar to AAC. One big difference is that the cost of a CLC production plant is much less than AAC allowing for easier entry into the market. Companies such as Greentec Construction Technologies (https://greentecct.com/) offer molds and equipment to start production.

Cellular lightweight concrete (CLC) is formed by combining compressed air with a liquid foaming agent, a foam is produced which is mixed with regular concrete leaving lots of tiny air pockets within the material.

October 3, 2018 - 10:44 am

I was told that they make these blocks in Mexico but do not know where to buy them.

February 26, 2018 - 1:44 pm

Hi All,

    I'm starting a AAC brinks manufacturing unit in India and am planning to export it. My unit is expected to be up and running by Aug 2018. Anyone who is interested in purchasing, please contact me. If anyone has any suggestions on how I can make my business successful, I'm all ears. 

Thanks,

Reddi

January 30, 2018 - 11:43 pm

I have over 3000 blocks available left on some property I purchased about 75 pallets wrapped in plastic if anyone is interested make me an offer located in Ocala Florida  Thanks Steve 352-216-1823

October 13, 2017 - 8:36 am

You are so right. You have to use special dry mortar for AAC. And that starts with the glue for the blocks. I sometimes see them put together with a layer of cement...and then they say AAC is to blame. Also AAC should not be put straight onto a cement or concrete slab. A layer of bitumus material should form the base.

July 23, 2017 - 8:28 pm

interesting comments from all contributers.

let me share with you my opinion:

i reside in the middle east, where the climate is known to have warm summers, especially in the arabian gulf where day temperature reaches on normal summer day 45 deg cel. combined with a high humid weather reaching 80%.

the use of AAC in the gulf region has been there since quite some time, the use of it is increasing mainly due to its impact on lowering the energy bill, plus the other synerical advantages (fire resistance, termite resistance, lighter than conventional blocks). Also they are used in high rise buildings, commercial buildings, villas. most of there use in non load bearing walls.

however; we see alot of plaster/render (stucco) cracks occuring on internal and external walls.

it is common here to use cement based plaster and renders for plasterworks, unfortunately the desingers here are not aware the importance of using a mix design suitabel for the AAC. many of them copy blindly the specs of plaster used over concrete (or cmu) and recommend using the same over AAC.

due to the low sttrength of AAC (~3 MPa), and the higher strength of stucco (> 8 MPa)  (astm c-926), several cracks appear shortly or later.

this has put many contractors and home owners in trouble for repairing their external painting which reflected the cracks beneath.

so i believe if AAC is to succeed then the specifiers need to study its impact on other building elements in parralel with other trades and adjust them accordingly. introducing one element for the sake of its properties alone will have its risks if not studied its compatibility with the rest of the components.

we try here to educate all stakeholders involved to use customised stucco mix designs which are not rich in cement. AAC walls can allow you to apply thin stucco (5 mm.) instead of the conventional 15-20 mm. and many stakeholders are not aware of this point.

conclusion:

it is important to be aware of the product charecteristics and how it behave with other building elements and other trades.

best regards.

November 9, 2015 - 5:13 am

Merhis Projects are an Australian Developer and Construction company and have been using their patented Merhis Building System for the last 4 years. They have completed a number of multi story mixed use residential and commercial buildings of more than 8+ levels and currently have five projects ranging from G+8 to G+16 at varying stages of completion.

They have designed a building system that incorporates hot rolled structural steel columns and beams with prefabricated steel reinforced AAC floor panels and wall panels. The result is a building system that is super fast in comparison to conventional reinforced concrete construction.

The company has embraced AAC product and by the speed they are building their investors are happy too.

Check out the link below for their time laps video.
Pretty amazing stuff....

https://vimeo.com/102488673
Password: livemerhis

Regards,

Simon

May 20, 2015 - 2:58 pm

I Have been in construction for many years and am now finishing my degree in mechanical engineering. I am truly amazed at reviews of many things and this is one. Some people have given poor reviews of AAC do to obviously poor installation and handling. AAC is a building material! If I got cracked improperly cured bricks and then installed them could I blame bricks?

Then someone is crying about how after using AAC they still needed heating and cooling? Not to say anything truly bad but, what makes anyone think that you can put up a single layer of a material and end the world energy crisis? My home is steel framed 2x8 exterior walls with r-30, 3/4 ply, foam board, tyvec, and brick and I need heating and cooling. The purpose to AAC is to reduce not eliminate.

I would ask that anyone reading this looks at any material the same way as follows:

Research installation procedure, manufacturing reviews, inspect the material, add insulation, moisture barriers but include proper airflow. Weep holes are used in masonry construction for a reason. Modern buildings are tight and need air flow. Use return air units with heat exchanger to bring in outside air without heat and cooling loss. Don't treat ANY material with its maximum advertised range. If my floor needs to be 40lb per square ft strong I will design for more and put it under less stress. Factor in real world situations and finally THEN report on the situation.

Also be sure to buy 100% prefabricated and cured AAC. On site cannot work as well as oven baked AAC cut with piano wire.

Germany has weather extremely comparable to many parts of USA and they build mainly in AAC. If you consider it's flaws and plan the installation accordingly you will have fantastic results.

And for anyone truly intrigued by modern construction, look at how many buildings are being built in an identical manner to 3D printing however, using AAC!!!

A residential home can be built in a weekend using this method. The structural part anyway. Imagine what can be done in the world of modular construction! Homes can be built like Legos if some thought is put into it. Pre drilled holes for MEP and EE, hell you have Simpson ties and connections pre embedded in there n we're talking about building a fortress!

January 23, 2015 - 2:56 pm

Hello, I am a sculptor and have been using AAC as my medium for a number of years and my supplier just dried up! I teach classes in it and use daily and need a supplier fast. Can anyone offer me any help?

thanks,
Carole

July 15, 2014 - 2:38 am

I have just built a house in Australia with an AAC floor. At 120lbs for 6ft by 2ft slabs, it is not lightweight. It is 3 inches thich with thin rebar through it and is supported on joists 18 inches apart. I chose it because it was fairly easy to lay and does not need protection from the weather as I knew it would be about 6 months before the house would be weatherproof.
I was suprised at how fragile it was. Do not work with it or even handle it when it is wet. It will crumble in your hands.
Do not drop it, support it thoroughly on both sides of the cut when cutting it, do not use a hammer drill, do not drill closer than 2 inches from an edge. It will break.
Provide additional joists around penetrations greater than 4 inches, eg all waste water pipes because the actual AAC has little strength itself.
Unless you cover the floor with boards, simply walking around on it will create a constantly dusty environment in the house until the carpets are laid.

April 21, 2014 - 12:41 am

After reading negative post on this forum, as a lifetime "Ecologically Sound" builder I have to post a positive response for AAC . Having lived in a celestory (clearstory) AAC home and an AAC Shop with adjoined Guest Quarters for 10 years, situated Above Prescott, AZ at 5800ft. altitude. The tempratures ranging from 5 degrees F. to 100 degrees F. with monsoons in summer, and snow in winter. We have infloor radiant heat, yet we seldom use more than a 1000 watt bathroom heater after baths or occasionally in the bedroom. The radiant heat is used less than 8 hrs. a day for two to three weeks in the harshest part of winter, and we have no AC period. The house was designed with a chimney effect, and electricly operated windows to open after the temp. goes down in the evening, and close when it rises in the morning during the summer. Though we have up to three feet of snow on and off through the winter, and monsoons that drop as much as much as 2 inches per hour in the summer, we have never had a mosture problem, and having lived in a cmu block house with brick veneer, the sound blocking of AAC is vastly superior. As to the spalling, since I have several hundred AAC ("Ecrete brand") block left over for a project after retirement which have been left on pallets in the open, with exception of a tarp which covers only the top layer of block, and they are in the same condition as when they were when left ten years ago. I have to assume mosture spalling complained of in this forum is due to improper manufacturing or installation.

BTW I am not opposed to other green building processes, in fact I moved to St. David in SW Arizona, to learn from the granfather of rammed earth, Tom Schmidt, the last, to my knowledge, to build rammed earth structures without using portland cement for stabilizing. In addition to Building the 4 ft thick St. David Holy Trinity Church, when I left for Prescott over ten years ago, Tom was 50% finished with a 3.5 million dollar hacienda and had finished his Bed& Breakfast, both built of pure earth.

I have also built homes of rammed earth,adobe, SIPS, ect. so I am not attached to AAC block, but it has proven to be a good product for me and some of my clients.

Ben

 

February 1, 2013 - 2:35 pm

Yesterday (Jan 31, 2013) was a pretty typical day. We left our condo at 730am and I turned off both heat pumps, as I usually do. The inside temperature at that point was where we usually keep the heat when we are there, i.e. 71 degrees. When we left the condo, it was about 35 degrees outside and the high temperature for the day was 52 and it was sunny and very windy with gusts up to 30 mph. When I got home at 4pm, the temperature registering for both thermostats was 70, i.e. a drop of one degree with no heat on all day. We do get some solar gain on the west side, and if it is overcast, the temperature drop inside is greater. However, it has never dropped below 65 even on a totally cloudy and/or rainy day, and even with external temperatures in the 30's all day.

February 1, 2013 - 1:30 pm

I thought some of you might like to hear the experiences of someone who actually lives in an AAC built condo. My wife and I have lived for 14 months in Clemson, SC in a five story AAC built mixed commercial/residential building. We own and occupy the entire 5th floor which consists of approximatley 3000 sq. ft. heated and cooled space. The ceilings are 10' 4" throughout the unit and we have six double windows and three sliding class doors leading to decks or balconies. I do not know the specifics of the construction other than it was AAC block.

Our average electric bill for the past 12 months was $72. We have a vented gas fireplace that we use for about a half hour a day, three months a year, but since it is vented, I'm guessing that it is not providing much net heat, if any. Heat/ac/water heating are all electric. We have a gas cook top that we use daily.

For comparison, we own a unit across the street that is approximately 1250 sq. ft. with conventional commercial construction. It has 9 ft ceilings, two double windows and one sliding glass door. It is also on the fifth floor of a five story building. We rent it, and the electric is in our name so we see the bills. Most months, the difference is less than $5 (our unit being higher), but some months the other unit is higher. There are also two people living there.

Other than the obvious low energy use, my wife and I are continually surprised how warm we feel in the winter and how comfortable we are in the summer. There just are no drafts at all. Prior to living in the condo across the street (which had drafts), we lived in a 4500 sq ft conventionally built house. The electric bills always exceeded $300 in the peak winter and summer months. Even though this house was built to high standards at the time, it was still drafty. And when animals invaded the walls and degraded the insulation, it was worse.

All numbers aside, the lack of drafts and the impossibility of animals in the walls is a huge factor for the consumer. I can honestly say that I would pay at least $10,000 more for an AAC structure compared to a similar unit without it.

I am more than willing to talk to any builder or consumer who is considering AAC, from the perspective of an end user. It's a really great product and I think that end users, once they become familiar with it, will more and more demand it. 

May 9, 2012 - 2:18 am

Thank you all for this excellent discussion. I have been designing a series of very small (600-800 sq ft) cottages specifing AAC and am very thankful for all of your inputs both pro and con.

I clearly realize now the importance of maintainining and clearly specifying a proper vapor proof exterior coating of some kind, especially here on the west ("wet") coast where rain forest precipiation is highly predictable and very determined, along with consistently huge seasonal variations in 24 hour  temperature cycles. I am convinced the material is perfect for the specs based on these on-site and in-the-field expereinces.

I would love to know the exact product you would recommend as a stucco coating, and wonder if such coatings need reapplication on a semi annual basis or if there is something with a fiber (or something else is included) that helps prevent cracking of the protective shell coating...

February 10, 2012 - 10:58 am

I am the Sales Engineer for Carolina AAC, LLC (CAAC). CAAC is currently constructing a new AAC manufacturing facility in Bennettsville, SC. Our blocks will be produced to US imperial units giving designers and contractors familiar units to work with. We anticipate having inventory available by June of 2012. We are very excited about the opportunity to provide AAC to the Piedmont region, mid-Atlantic, and northern climates.

While it is true that AAC is popular in European markets, it is misleading to say the climate is mild. AAC is used throughout Germany from its southern border to the shores of the North Sea. As I write this, the temperature in Hamburg is 30 F with overnight low of 13 F (northern city) and Munich is 18 F with overnight low of 9 F (southern city).

If you have any questions about AAC use or pricing, please do not hesitate to visit Carolina AAC at:

www.CarolinaAAC.net

We look forward to continuing the conversation about AAC use in the US.

Kind Regards,

Bruce Weems
Sales Engineer

Carolina AAC, LLC

February 8, 2012 - 2:42 pm

Further to the above, something of a hands-on backgrounder for the non-believers out there--go here:

http://www.cement.org/homes/AAC_projects.asp

As for the dynamic benefit of a massive wall system, think: Superior Inherent Thermal Insulation

"AAC has extraordinary thermal insulating qualities. A low thermal conductivity (U value) combined with the thermal mass effect results in a 10" wall that yields an R-31 equivalent rating. That by far outperforms wood and concrete masonry."

" '[S]teady state' thermal values obtained from laboratory testing [assume] that temperatures at both sides of a wall are constant and remain constant for a period of time, unlike what actually occurs in normal conditions. In actual conditions, the temperature levels on both sides of walls may change during a 24-hour period. In many cases, the exterior temperature may experience large temperature swings. These changes may cause a reversal in direction of the heat flow or at the least, 'delay' the heat flow to the point where it substantially reduces the heat [or cold] transfer to the inside the building envelope."

"This dynamic process is known as the 'thermal mass benefit' or 'mass-enhanced' R-value."

"Consequently, AAC lowers energy costs for cooling and heating, and makes the use of additional thermal insulation unnecessary."

To Green, Energy-Efficient High Performance Buildings

Dollars & Sense Associates
www.aac-nw.com

February 3, 2012 - 9:08 am

A suggestion, I notice that Buidingreen has never done a feature on earth berming. We are designing an eco resort in south India and have considered earth berming one of the structures. I would love to know what the experts at Buildingreen thing about this centuries old concept.

February 3, 2012 - 4:39 am

One thing about AAC I forgot:

Because it's produced in accurate molds and has smooth edge surfaces, you can throw up a light-duty building in almost no time by just dry-laying the blocks and giving the completed walls a coat or two of fiber-reinforced mortar or plaster on each side to hold them together.

Don't just take my word for it - read the blurb.

February 3, 2012 - 7:26 pm

My use of AAC has been somewhat limited, but I'm finding myself more and more drawn to it. I first erected a 60 SF free-standing 7' high x 9' long wall out of 8" block on my own, and I think most people would feel quite comfortable in stating that I am not an accomplished mason. In fact, prior to building this wall, I had never done any masonry whatsoever. 6 years later, the wall is still standing there in perfect condition. At work (I'm a RE Developer and GC), we recently incorporated 4" blocks for partitions between cellar mechanical rooms to get more familiar with the material. One room per the original plan turned out to be too narrow for the fire pump that needed to be installed within, while the adjacent room had space to spare. Our mason picked up a sawzall, cut through the AAC at all four joints, pushed the wall over a few inches, and reset it in place with the supplied mortar. All within about an hour or two. No debris resulted from this change. Try doing this with a CMU wall and see where it leads you....

February 3, 2012 - 11:03 am

FortenatoUSA LLC will soon be bringing to the market System5zero, a new composite building system which employs stucco-finished AAC. It is created to integrate with North American building practices and will be a valuable building system in cold-dry northern climates as well as hot-moist southern climates. It will have high thermal resistance with zero maintenance.

February 3, 2012 - 10:26 am

I appreciate all the comments that have been written above, like anything else numbers and material information can be manipualted to defend any point of view, howvere the facts are that AAC has and continues to have a very large market share of the construction product market around the world. The materials adaptive ability allows it to perform significantly better, even in near arctic regions such as Scandinavia, than most conventional products in most regions of the world and exceptionally better in moderate climates. AAC is manufactured in plants that are solely designed for their precise production with the flexibility to create masonry and reinforced structural and non structural building systems unlike any block or precast concrete plant. AAC, while light weight does provide structural ability whether field reinforced AAC masonry or plant reinforced AAC panels for up to six stories and as infill in high rise construction in most regions of the USA and the world. The material can be used as an entire structural building sytem as the designer sees fit.The biggest issue is that AAC manufacturing plants are significantly more costly to build than convetional block or precast concrete plants. The product is designed to use waste materials such as very fine waste sand, fly ash or bottom ash and mine tailings making it a truly sustainable product. AAC uses a very small amount of cement in the maufacturing process and significantly reduces the carbon footprint as compared to conventional concrete products. AAC is and has been maufactured in the USA since 1996 and manufactures products in sizes driven by the masonry and precast concrete industry. The diffrence is that AAC is made as a precision product to much tighter tolerances than required by the industry. This is inherent in AAC manufacturing facilities world wide and this quality control process has been adopted by the US manufacturers.
The other issue is that there are currently only a few sources for the material and the shipping costs can make the material less attractive in some regions of the USA.
There are thousands of AAC projects built in the US since 1996 and the uses varying from a simple single family home to the Strategic Computing Center at Los Alamos, New Mexico. We have built multifamily, schools, hospitals, studnet housing dormitories, big box stores, hotels, motels, sound barrier walls and even coal mine air stop seperation walls. These projects are still exceeding the designers and owners expectations for perfomance in almost all cases.
We need more AAC Manufacturing Plants in the USA
PS: david White you can cut and Rout AAC with a dado blade or router and we do it all the time to accomodate conduit or low voltage wiring.

February 3, 2012 - 7:43 am

I've heard AAC can be easily routed out for electrical work, for instance using a dado on a circular saw. Can anyone comment on this?

February 2, 2012 - 7:59 pm

I am an architect that has designed with AAC for buildings in NJ. Since some sections of NJ require union labor, we though it would be a good idea to present the product to the local union hall. Aercon provided product to the union workers who were quickly trained how to work with the product. They approached it with scepticism, as did I at first, but they very quickly began to embrace the product. Albiet, they saw it as a way to compete for the work of carpenters but also realized that from their standpoint, it was not much different from laying a concrete block but the reduced weight alone was a huge plus for the workers. And because each block is larger and ligher, they could produce much more in day which could significantly lower the installation labor cost. There are many advantages to AAC that significantly out weigh the disadvantages. One just has to be open minded and try to use the product in its purest form. Don't try to just simply replace a concrete block for AAC. Be creative, stay simple and the product will perform as advertised. Trust me, your building will be so tight that your HVAC designer will have to account for this. I would not hesitate to use AAC and am confident that if it was marketed properly, you are going to see much more of it used in the future.

February 2, 2012 - 7:13 pm

Hello,

I'm glad to see you folks have re-visited AAC, after how long?

You asked for comments and you got them, adding much to the article, especially Tony Marshallsay's re "Drawbacks? Really?"

The links are a plus. Thank you all.

Here's one you may wish to view. The Building of Syon Abbey:
http://www.syonabbey.org/Building/building2.html

There's another AAC build that is never discussed: The Nicholas C. Metropolis Center at Los Alamos. Hensel Phelps at the helm of that project.

CTL Group, published “Building Code Acceptance Tests for Autoclaved Aerated Concrete (AAC) Products” a year or two ago. Worth reading but it is no longer available on their website and I can't find it. I asked for their help two weeks ago to update our B2B page at Thunderbird--but no response as of yet.

Some points set out in the article surprised and pleased, e.g., the statement by the SafeCrete person--a surprise.

The response from AERCON FL fixes an oversight.

Milder weather in Europe--then there's Scandinavia to consider. Really? Recent developments in the Yakutsk region of Russia's Sakha Republic are worth noting.

To Buildings That Work Harder & Smarter...

Dollars & Sense Associates
www.aac-nw.com

February 2, 2012 - 10:11 am

I wanted to correct one thing that this article failed to mention. The only manufacture of AAC in North America is AERCON FLORIDA, which is located in Haines City, Florida. We have been in business for 10+ years after purchasing an YTONG plant in the late 1990's. Rest assured AERCON does manufacture our product in North America and ships to all places. Please feel free to contact us with any questions or concerns.

Best Regards,

Mike Quaka
Vice President - General Manager
AERCON FLORIDA, LLC
http://www.aerconaac.com

February 2, 2012 - 4:52 am

One of the things that appeals to me about AAC is that it's forgiving of moisture flow--moisture migrating into it and even condensing (if it gets cold enough) shouldn't cause problems they way it might in a wood or steel-framed wall system. Cementitious materials are great for discouraging mold growth, for example.

But if that added moisture severely compromises the thermal performance, as noted above, that's more of a problem. I doubt that effect is linear, but I certainly believe it could be substantial.

February 2, 2012 - 4:41 pm

I am an independent representative in Maryland for Aercon AAC, and am happy to provide price lists and technical assistance (dlevy@greenspringbuildingsystems.com). Aercon produces block, lintels, and steel reinforced panels.

In 1999 I used AAC to build an addition to a home I owned in Baltimore County. I was well aware of the use of AAC in Europe, wondered why it wasn't better known in the US, and decided to try it for myself. I found it very easy to use, both for cutting and installation, and was entirely pleased with its performance.

Though I couldn't quantify energy use, I extended the existing hydronic system using one-fourth the capacity HVAC contractors recommended, and it worked quite well. The addition was noticeably quieter and draft free than the rest of the building, 1954 construction of frame with masonry veneer.

I purchased a Lissmac masonry cutting band saw, which is similar to a woodworking band saw with the addition of a sliding table. AAC can also be cut with hand tools, as other posts have mentioned, and carbide-tipped tools designed specifically for AAC are readily available.

Today I would add exterior insulation to meet the Passive House standard. I am a certified US Passive House consultant, and am actively seeking AAC Passive House projects.

February 2, 2012 - 2:40 pm

AERCON manufactures autoclaved aerated concrete here in the United States and has done so for a decade now. Our manufacturing facility here was built and previously operated by YTONG. I would urge any of you interested in AAC to visit our website at www.aerconaac.com. I cannot begin to address each of these comments individually but would like to welcome you to contact us for further information. We have inhouse technical support, engineering and are pleased to provide pricing on request.
Thank you.

February 2, 2012 - 1:00 pm

We built a small cottage in central Wisconsin with AAC purchased from SafeCrete near Atlanta. We also toured the Aercon plant in Florida, but the shipping distance was greater for us. Both businesses were extremely helpful. This is important especially because we were a small account. My husband and I built the AAC walls ourselves - which says how easy it is to do as we are "retirement age." Our profession is in IT, not masonry. The walls were incredibly square. For the exterior we used foam board under cladding (stone and cedar). One interior wall separates the garage from the living area.

Other benefits are...
- Adding wall tile to the interior surface - a breeze
- Using plaster for interior walls - marvelous
- Not having to look for studs to nail into, but attaching items where you want them, letting us fit items in the small utility room - fantastic. This was true with the cabinets in the kitchen & bath as well.
- The sound and fire insulative quality - super, especially for fire as we are in a forest area
- A tiled, low-walled walk in shower - no glass or curtains needed - plus serves as a shelf.
- If you estimate requirements well, there is very little construction waste.
- Low VOC, low pest invasion, low thermal bridging

We have in-floor electric heating but use primarily a small woodstove. I have no accurate numbers for energy use, but from looking at the bill and the woodpile, it appears to be very low. It is also very comfortable in summer.

In short, it’s an elegant wall sandwich and we are enjoying the comfort tremendously. We would like to build another and try some new ideas. We initiated, funded, and contracted the project ourselves. We did our own research and design. The building inspectors were most cooperative and showed a real interest.

February 2, 2012 - 12:57 pm

Hi there,
15 years ago I built a strawbale house in VT and used AAC blocks (then manufactured by Ytong in FL) for all interior partition walls in the house.
They were easy to put up (I hired a mason to do part of that work) set directly on the slab with rebar drilled to hold the bottom in place) we site poured headers out of concrete where applicable, although Ytong offered precast options for those locations) I used 4", 6" and 12" blocks depending on the situation. There is plenty of load bearing capacity in AAC to substitute for a 2x4 or even 2x6 wall. In Germany AAC is offered in 3 or 4 different densities with higher R-values achieved in lower densities. R-values are similar to Mineral wool or Cellulose dens pack in the R3.5 range. Often houses will have a core of load bearing AAC with lighter elements up to 12" thick glued on the outside for an overall R-value in the mid 40ties. Air tight, not sure what the responder above means by saying that CMU andAAC is not airtight. Maybe not vapor tight, but air tight for sure. There have been numerous Passiv Houses constructed using AAC.
http://www.ytong-silka.de/de/docs/Ytong_Multipor_WDVS_042010.pdf
I think the main adoption problem is that single family residential construction in the US is geared completely towards wood (maybe with the SW as showing some exceptions), there is not sufficient familiarity with masonry construction with architects and builders in that field. Urban construction where masonry is used a lot is dominated by the concrete and steel industries, for obvious static reasons. That leaves a comparatively small market of low-rise multi-party buildings.

To the responder from NM above: if you have mold on masonry, you have a leaking stucco system. AAC should not be finished with cement stucco, it is hydroscopic and not vapor permeable enough.

All in all I would build an entire house out of the stuff, it is easy to do yourself, even with only basic masonry skills, you can saw it by hand and glue it like foam blocks. If Xella starts offering this material in a coherent system again in the US it might catch on, but I think they have been too busy consolidating their AAC empire worldwide to pay attention and their web presence, marketing and sales strategies in the country have always been abysmal, my experience with them was before Ytong was bought up and was o.k. Later attempts to get information, pricing etc from Hebel have been terrible.

The sound deadening properties are o.k., I agree that they are not much better than a 2x6 wall insulated, but they retain heat much better.

best,

Niko

February 2, 2012 - 11:49 am

I currently live in the American Southwest, in an adobe house, with a one-room addition built in AAC, as well as a small AAC outbuilding. If this region is supposed to be the best for AAC, then I marvel that AAC is accepted anywhere.

We have moisture problems, cracking, and spalling. This is the only room in the house which shows interior mold on the walls, a rare problem in this climate. Many of the AAC blocks appear to have been physically damaged during transport or installation, especially in the outbuilding. Perhaps the builder sorted out all the broken or nicked blocks, and intentionally used them for that building, but the damage rate was apparently high. Even with our dry climate, I think these AAC blocks need more moisture and rain protection than the cement stucco that they have. I think the spalling has been caused by absorbed water freezing in the bricks.

The supposed insulation value, which the builders and manufacturers tout, is clearly insufficient for this climate, both winter and summer. If there is any thermal mass effect, it is not sufficient to make this room comfortable without supplemental heat or cooling, three seasons a year. Our Spring's large daily temperature swings would maximize the supposed thermal advantage, but this room still needs heat.

While they must offer some soundproofing, our AAC blocks don't strike me as particularly effective. It's easy to compare to the adjacent adobe walls, and the AAC is much less effective at curtailing sound transmission. Based on my experience, I think these AAC blocks transmit sound better than brick, CMUs, or strawbales. They don't seem that much different than insulated, cement-stuccoed 2x6 frame walls, although somewhat better than 2x4 walls.

I don't know how our AAC blocks compare with those of other manufacturers, but I am not tempted to use them in the future.

February 1, 2012 - 9:39 pm

Re AAC Drawbacks:

"...These often need to be sawed, adding labor and fuss to a building system that's supposed to be simple." That's no different than working with timber, and you can use the same saws - they get blunt quicker, sure, but they'll cut AAC pretty well even when blunt.

"Since right now your AAC is most likely coming from Mexico, the advantages offered by lighter weight will diminish significantly as the mileage increases." This is a purely US disadvantage - until you start producing it at home again.

"Thermal properties are better than those of conventional concrete, but they aren't good enough to make AAC a viable wall material (relative to BuildingGreen-recommended R-values) in most U.S. and Canadian climates without additional insulation." So what? Most external walls need some additional insulation - the question is: how much?

"The European climate, where AAC is popular, is milder." Tell that to the folks in Central Europe, where winter temperatures regularly get down to -20°C and in the current cold snap have been down to -39°C.

"Unless rebar is added--which adds to the weight and amount of material in the blocks--AAC can only be used for low- and mid-rise construction. But it seems to be popular for single-family homes as well as schools." It's not intended for high-rise construction, is it? For low- and mid-rise construction it does pretty well; and for high-rise it works for non-load-bearing walls - and is also frequently used for interstitial services floors. Also, it can be produced with integral reinforcement - but usually mesh, not rebar.

"Unlike conventional concrete, AAC can't be used as a finish; it is more porous and needs cladding or stucco on the outside so it won't absorb moisture." Just like CMUs.

Drawbacks? Really?

February 2, 2012 - 3:31 am

Tony, do you have any theories on why AAC hasn't caught on in the U.S.? I see your logic, but that still leaves me wondering why it's not more popular, given its advantages.

February 2, 2012 - 2:33 am

Robert, your muffins sound like an admirable building material. What would you recommend for the mortar?

February 2, 2012 - 4:11 am

Robert brought up a good point about the sand, and I've added something to explain that. Someone with a background in the chemistry of concrete might have more to add, which would be great. I think it is mainly a question of semantics.

Yusuf, I think that suitability for moist climates would depend on what's in the rest of the wall assembly. If it has drying potential, then moisture shouldn't be a problem, but if you started introducing materials that act as vapor barriers, the results might be harder to predict.

February 2, 2012 - 11:29 am

we have used it in a couple of projects. Once for a 2 family home, where we used 8" block with a sider-oxydro stucco finish. We had some leak issues, and i've been concerned that with the bond beams and reinforcement and cored blocks that the R value is often compromised. The client is happy though with the tightness of the house and feels it doesn't cost much to heat.
We are also using 12" blocks as back up for brick and for a trespa rain screen on a project going up now in NYC. Masons said it was easy to work with. We haven't had any issues yet, but have had to be careful they use the right screws for brick anchors etc. These are face mounted, and the size of the block has not been an issue - its been easy to channel out for electrical fixtures etc. We chose it for insulation and lower embodied energy reasons, although now we would make sure we added another layer of continuous insulation.