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Community and Q&A

Exterior Insulation For AAC

Desert_Sasquatch | Posted in Green Products and Materials on

I’m designing a home for climate zone 6 (Rocky Mountains) and one of the options I’m looking at is AAC (Autoclaved Aerated Concrete).  I like that it’s bug and especially mouse-proof, I like the aesthetic, I like that it’s fireproof and fairly durable, and I also like that I won’t need to use teflon-based air barriers to do it right. 

That said…I’m coming to understanding that the higher R values I saw quoted (R-2.4 per inch) were “equivalent” and probably only valid in Florida.  And that the real R value of 1.1 per inch is not going to give me as much insulation as I’d like. 

One solution to this is to use rockwool on the exterior and cover it–using a rainscreen construction–with hardiboard or metal siding.  It’s a decent solution that I know will work.  Mice might get into it but at least they wouldn’t be in the home. 

The other option comes from reading that in europe they sometimes use two courses of AAC–one which is structural (has relatively more cement) and one which is for insulation (has relatively less cement).  In the USA I gather we do not have the non-structural kind of AAC, but I wonder about using aircrete instead. 

Have folks done this before?  I don’t fancy being a trailblazer with building materials, I’d prefer to do something more tried-and-true.  But the idea of being able to use aircrete as insulation is appealing, since it seems like it would make things a lot simpler.  And admittedly, I was looking forward to having an exterior wall that could be finished with lime wash–mostly for aesthetic reason.

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