[Greenbuilding] FW: Aerated Autoclaved Concrete

Tue Feb 5 19:02:05 CST 2008

AAC is definitely an interesting product. 
It is, however, cheaper and easier to produce a wood frame wall that outperforms an AAC wall if you build it properly. The walls (and likely windows and ductwork) of you neighbors' house are likely not done well.
AAC is great for impact, fire and termite resistance. It certainly has its place and should be used in more applications, particularily institutional and commercial, but the arguments for homes is weak. 
The best climate zones for AAC are hurricane coastal zones (although designing the roof tie downs in a corrosion resistant manner makes this an expensive and annoying option) and the southwest (where it really might be a lower cost way of building durable and lower energy homes).

The percentage of homes in Europe using AAC is dropping (and I doubt it was ever 60% in any country), as it is difficult to get to the required R-value in the countries which were traditionally AAC strong, eg Sweden, Germany, Britain. If you need true R-value of 20-25, AAC walls get too thick. AAC makes more sense in Georgia, where R10-12 is a R-value decent today (if you are competing with 2x4 wall with R12 batt or other pathetic walls). We might catch on eventually here too, and require higher R-values.
Another reason for the dropping AAC sales is that people are switching to other more natural and lower embodied energy building systems, like, er, wood! Hard to understand those crazy Europeans, eh, asking for high R-values and wanting low energy renewable building materials that grow on trees. AAC is hardly a low embodied energy material, using more energy per unit mass than concrete. Of course, you dont need to use that much mass, since AAC contains a lot of air. Even so, a 8" AAC wall uses a lot more energy than a 2x6 wall with cellulose insulation (to me, the obvious comparison). 

But if you expect a flood anytime soon, I would choose the AAC every time.

PS and BTW Jeannie: are you connected to the Babb family that is producing AAC in the South east under license to Hebel?

Jeannie Babb Taylor wrote:
> I live in an AAC home (walls only 8 inches thick) and my heating/cooling
> bills are significantly lower than my neighbors' with smaller homes, in
> spite of my high ceilings and large windows.  Call it "drivel" if you want,
> but you wouldn't think so if you were the one paying the electric bill.  ;-)
> 
> AAC is not only a thermal mass system.  It has insulating properties as
> well.
> 
> I am in Georgia but there are AAC homes all over the US, including a good
> number in Oregon.  It's a "hard sell" in the US because Americans have no
> conscience about cutting trees and producing high-energy, high-waste, toxic
> building products.  Most people (especially spec builders) just want to
> purchase the cheapest home possible.  If they aren't the one paying the
> heating/cooling cost, what do they care about performance?  Nor do they care
> how well the structure will hold up over the next 30 years.  
> 
> In Europe, it's a different story.  Something like 60% of residential
> construction is AAC.  Why would it be so popular for 80 years if it didn't
> work?
> 
> Many architects are exciting about AAC, not just for its thermal properties
> but because it has the highest fire rating on the market, is more green than
> most building products, does not off-gas, saves on jobsite waste, etc.
> 
> For full disclosure, I have interest in the lumber and AAC industries. I
> spend most of my days selling lumber, but if I were going to build another
> house, it would without a doubt be AAC.
> 
> Jeannie
> 
> 
> -----Original Message-----
> From: greenbuilding-bounces at listserv.repp.org
> [mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Lawrence Lile
> Sent: Tuesday, February 05, 2008 10:15 AM
> To: Jan Fillinger; greenbuilding at listserv.repp.org
> Subject: Re: [Greenbuilding] [BULK] FW: Aerated Autoclaved Concrete
> 
>> Despite that, the
> proponenets state that the "effective" is  R-value is much higher due to
> the "Dynamic Benefit of Massive Systems
> 
> This drivel has been promulgated for years by people who come up with
> poorly insulated materials that are massive and can't figure any other
> way to market them.  Log home dealers are also notorious for using this
> line. If it could dip below zero for an hour and then climb back up to
> 70F, massive materials would be OK, but it never does that.  When it is
> sub-zero outside for several days, any effect due to mass is over with,
> and you are going to miss your insulation and your house won't retain
> heat very well.  Insulate your wall and forget about this stuff.  People
> evangelize about stuff because it needs a hard sell, if it was really so
> great they wouldn't need to work so hard.  
> 
> I could see using a material like this in a climate like New Mexico,
> where it gets cool at night but always warms up in the day.  One night
> you might be able to use the mass to some effect.  But a conventional
> wall and some masonry inside will buy you the same thing.  
> 
> 
> Lawrence Lile, PE, LEED AP
> Project Solutions Engineering
> 
> -----Original Message-----
> From: greenbuilding-bounces at listserv.repp.org
> [mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Jan
> Fillinger
> Sent: Monday, February 04, 2008 2:09 PM
> To: greenbuilding at listserv.repp.org
> Cc: 'Mark Piepkorn'
> Subject: [BULK] [Greenbuilding] FW: Aerated Autoclaved Concrete
> Importance: Low
> 
> Hello:
> 
>  
> 
> I am designing an off-grid house in the Bend area of Oregon (high desert
> climate, 340+ days of sun, winter lows around 20-30 deg, summer highs
> around
> 95-95 deg, summer RH of 15 to 35%) that will be mainly solar-heated.  We
> have modeled the house with the Energy-Scheming software developed by
> University of Oregon professor G.Z. Brown.  We know that the sun will
> provide about 95% of the heat required to maintain comfort, as long as
> we
> provide a sufficient amount of solar glazing, internal thermal mass, and
> well insulated envelope.  The basic heating strategy is: solar heat gain
> through large south facing glass (properly shaded against summer
> radiation,
> of course), large surfaces of 4" thick thermal mass surfaces exposed to
> the
> indoor air, and a tight well-insulated envelope.
> 
>  
> 
> Originally, the thought was to use staggered 2x4 @ 12" oc staggered on a
> 2 x
> 6 plate, so as to eliminate direct thermal bridging through the studs,
> and
> all cavities filled with closed-cell polyurethane foam which eliminates
> any
> infiltration. In order to meet the thermal mass heat storage needs as
> defined by the computer program, in addition to a 5" slab (fully
> insulated
> with rigid insulation underneath and around the perimeter), we were
> planning
> to add 4" brick or concrete block veneer on the inside of the open
> public
> spaces receiving the majority of solar heat gain.
> 
>  
> 
> However, I recently met with several contractors who have been building
> Aerated Autoclaved Concrete (AAC) block homes around Bend.  This product
> was
> originally developed in Germany under the name of Hebel.  
> 
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> 
> 
> 

-- 
Dr John Straube, P.Eng.
Associate Professor
Dept of Civil Engineering & School of Architecture
University of Waterloo
Waterloo, ON Canada