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.


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. 

The concrete is poured into molds, left to rise, and the "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.

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 muffines, 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:

1. It uses less material-important for concrete, since portland cement is one of the most       energy- and carbon-intensive building materials.

2. 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 haven't found anyone to challenge those claims, but are still looking for data).

3. It's lighter, which cuts down on transportation costs and fuel use.

4. 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).

5. Air leakage is minimal.

6. AAC also has excellent soundproofing properties.

7. 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:

1. 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.

2. AAC requires a learning curve for builders, because the mortar application is more           precise.

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

1. 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 lavor 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.)

2. Since right now your AAC is most likely coming from Mexico, the adbantages offered by      lighter weight will diminish significantly as the mileage increases.

3.Thermal properties are better than those of conventional concrete, but they are not             good enough to make AAC a viable wall material (relative to Building Green-                       recommended R-values) in most U.S. and Canadian climates without additional               insulation. (The European climate, where AAC is popular, is milder.)

4. 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.

5. 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.


Would you use AAC?

That said, AAC does appear to have significant advantages for applicatons where conventional concrete would normally be the best material - like in the American Southwest and in other climates where thermal mass can increase the "effctive" 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 emprical 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?

Posted by Paula Melton on February 1, 2012


Comments

I am a commercial builder in Maeylan
Andrew Marani
Wed, 2012-02-01 12:54

I am a commercial builder in Maryland. We tried to use AAC on two projects several years ago. We could not get pricing quotes from suppliers either time despite a great deal of effort on my part. I really wanted to try this stuff out. I had a couple of masons convinced as well. But lack of pricing meant throw the wuppliers under the bus. but...

I wanted to use AAC for the demising walls on some high end condos. The fire ratings and high sound proofing would have made for a great wall. But without pricing we went to GWB with some special details.

I think AAC would be a good substitute for CMU walls, but if you are using concrete for a wall you are probably picking up some serious loads and AAC likely won't cut it.



First, I don't used buttermilk 
Robert Riversong
Wed, 2012-02-01 15:39

First, I don't used buttermilk in my muffin batter, nor do I use baking soda-most bakers use baking powder with aluminum compounds, which may be linked to Alzheimer's disease - I use non-aluminum baking powder. And my muffins are not "porous and light" but rich and dense.

You say that AAC is "similar to other concrete types, except that it contains no aggregate; sand or fly ash is included". You mean it contains no coarse aggregate, since sand is fine aggregate, and the mix won't harden into calcium silicate hydrates without the silica. While the reaction produces hydrogen bubbles, it is exchanged with air before use.

AAC is somewhat porous, depending on the precise mix density, size and configuration of pores, and it is certainly not an air barrier by itself-any more than are CMUs without a stucco coating.

While the R-value is approximately a 10-fold improvement over conventional concrete, because it is so porous and hygroscopic AAC will increase 42% in thermal conductivity with each 15 increase in moisture content by weight.

And the thermal mass value is quite poor-about double that of packed snow(the thermal mass index, which is the product of thermal conductivity and volumetric heat capacity, is about 1/60 of concrete). "In consistently cold climate, the savings may be somewhat less because this material has lower thermal mass than other types of concrete." -Portland Cement Association

Additionally, it's probably more appropriate to compare embodied energy with CMUs, not poured concrete: "with respec to embodied energy, AAC consumes approximately 50% and 20% less energy than that needed to produce concrete and CMUs, respectively." - Autoclaved Aerated Concrete as a Green Building Material, Stefan Schnitzler, October 2006, UC Davis Extension.


So it is no wonder that AAC has not caught on in th US. The advantages are highly overrated.



AAC worked wonderfully well for us in India
Yusuf
Thu, 2012-02-02 00:42

AAC worked wonderfully well for us in India. We have been able to do away with insulation altogether in our projects. Thereby justifying the additional cost over flyash and red sand bricks. I did know about the subatantial increase in thermal conductivity with such little increase in moisture content. So does this mean that AAC blocks may not be suitable for coastal regions?




Unreinforced Masonry
James Getaz
Thu, 2012-02-02 12:14

"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."

You may want to check building codes in earthquake areas before recommending unreinforced masonry (URM). California has made many owners spend lots of money in the recent past to strngthen URM structures, many low-rise. Building schools with URM today seems a particularly good way to get big headlines after an earthquake.



Used AAC Block 
Clare Miflin
Thu, 2012-02-02 12:29

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 have 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 does not 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 electircal 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.



Robert brought up a good point about the sand
Paula Melton
Thu, 2012-02-02 05:11 

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 should't be a problem, but if you started introducing materials that act as vapor barriers, the results might be harder to predict.



Re AAC Deawbacks
Tony Marshallsay
Wed, 2012-02-01 22:39

Re AAC Drawbacks:

:...These often need to be sawed, adding labor and fuss to a building system that is supposed to be simple." That's no different than working with timber, and you cann use the same saws- they get blunt quicker, sure, but they will 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 are not good enough to make AAC a viable wall material (relative to Building Green - 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 centigrade and in the current cold snap have been down to - 39 centigrade.

"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 is 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 intergral 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.



AAC not for me
Koninda
Thu, 2012-02-02 12:49

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 is easy to compare to the adjaceng adobe walls, and bthe 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 manufcturers, but I am not tempted to use in the future.



AAC - strawbale combo in VT
Nikolaus Horster
Thu, 2012-02-02 13:57

Hi there, 15 years ago I built a strawbale house in VT and used AAC blocks (then manufctured by Ytong in FL) for all interio rpartition 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 Ce;;i;pse dems [acl om yje 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 and AAC is mot airtight. Maybe not vapor tight, but air tight for sure. There have been numerous Passiv Houses constructed using AAC. 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 domminated 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 ok. Later attempts to get information, priceing etc from Hebel have been terrible. 

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




We built a small cottage 
Grace Spitz
Thu, 2012-02-02 14:00

We built a small cottage in cnetral 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 walss - 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 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 is an elegant wall sandwich and we are enjoying the comfort tremendously. We would like to build another and try some new ideas. We did our own research and design. The building inspectors were most cooperative and showed a real interest.


AAC is readily available to purchase in the US..
AERCON FloridaR
Thu, 2012-02-02 15:40

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 can't 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.



AAC in the Mid-Atlantic
Daniel Levy
Thu, 2012-02-02 17:41

I am an independent representative in Maryland for Aercon AAC, and am happy to provide price lists and technical assistance. 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 availabel.

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.



One of the things that appeal
Nadav Malin
Thu, 2012-02-02 05:52

One of the things that appeals to me about AAC is that it is 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 perfomance, as noted above, that's more of a problem. I doubt that effect is linear, but I certainly believe it could be substantial.



I wanted to correct one thing
Mike Quaka
Thu, 2012-02-02 11:11

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.



AAC Generally
Jeff Ramsdell
Thu, 2012-02-02 20:13

Hello,
I am 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 nothing.

To Buildings That Work Harder＆Smarter



AAC
Richard Vivenzio
Thu, 2012-02-02 20:59


I am an architect that has designed with AAC for buildings in NJ. Since some sections of NJ. Since some sections of NJ require union labor, we though it would be a good idea to present to product to the local union hall.  Aercon provided product to the union workeds who were quickly trained how to work with the product. Thry 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 workeds. And because each block is larger and lighter, they could produce much more in day which coule significantly lower the installation labor cost. There are many advantages to AAC that significantly out weigh the disadvantages. One just has to be opern 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.



Electircal work
David White
Fri, 2012-02-03 08:43

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




I appreciate all the comments
Angelo Coduto
Fri, 2012-02-03 11:26

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 i plants that are solely designed for their precise production with the flexbility to crete 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 system as the designer sees fit. The biggest issue is that AAC manufcturing 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 manufacturing process and significantly reduces the carbon footprint as compared to conbentional concrete products. AAC is and has been manufactured 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 contral process has been adopted by the US manufcturers. 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, student 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 performance 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.




Fortenato USA LLC will soon be... 
Frank Riepe
Fri, 2012-02-03 12:03

Fortenato US LLC will soon be bringing to the market System 5 zero, a new composite building system which employs stucco-finished AAC. It is cearted to intergrate 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.




My use of AAC has been somewhat limited, but I's 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...




One thing about AAC i forget:
Tony Marshallsay
Fri, 2012-02-03 05:39

One thing about AAC I forgot:

Because it is 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.






A suggestion, I notice that B
Yusuf
Fri, 2012-02-03 10:08

A suggestion, I notice that Buildingreen 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.




AAC, "The Right Stuff"
Jeff Ramsdell
Wed, 2012-02-08 15:42

Further to the above, something of a hands-on backgrounder for the mom-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 extraordianry 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."

" Steady state termal values obtained from laboratory testing 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 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 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




Carolina AAC, LLC
Bruce Weems
Fir, 2012-02-10 11:58

I am the Sales Enginner foer 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).




thank you for this very current and spot-on AAC discussion
Eric Wallen
Wed, 2012-05-09 02:18

Thank you all for this excellent discussion. I have been degining a series of very small cottages specifing AAC and am very thankful for all of your iputs both pro and con.

I clearly realize now the importance of maintaining and clearly specifying a proper vapor proof exterior coating of some kind, especially here on the west 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 that helps prevent cracking of the protective shell coating...




I thought some of you might like to ...
mark malmgren
Fri, 2013-02-01 14:30

I thoutht some of you might like to hear the experiences of someone who actually lives in an AAC bult 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 approximately 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 electirc 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 $10000 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.




one more thing 
mark malmgren
Fri, 2013-02-01 15:35

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.





AAC block 
Ben Brewer 
Mon, 2014-04-21 00:41

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 (clear story) AAC home and an AAC Shop with adjoined Guest Quarters for 10 years, situated Above Prescott, AZ at 5800 ft. 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 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 grandfather 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 yjocl Sy.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.




AAC for flooring 
The University of ...
Tue, 2014-07-15 02:38

I have just built a house in Australia with an AAC floor. At 120 lbs for 6ft by 2ft slabs, it is not lightweight. It is 3 inches thick 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, wupport 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, all waste water pipes because the actual AAC has little strength itself.

Unlessyou cover the floor with boards, simply walking around on it will crete a constantly dusty environment in the house until the carpets are laid.




Does anyone know of a distributor in Oregon or in the NW?
Carole Murphy 
Fri, 2015-01-23 15:56

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?




Amazing reviews...not in a good way
City College of N...
Wed, 2015-05-20 14:58

I have heen 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 
insatllation 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 anthing 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 sa 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 is flwas 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. Predrilled holes for MEP and EE, hell you have Simpson ties and connections pre embedded i there we're talking about building a fortress!