Hi all I am about to start building our family house. As I am in an earhtquake zone we need to have a concrete reinforced skeleton, with the concrete columns being 20cm thick. My architect thinks we should then build 20cm Ytong (or other AAC) blocks in line with the concrete columns, wrap the whole thing in 5cm of eps polystyrene and render over the whole thing. I am in a building zone where we are required to finish at least 70% of the house in stone, but the architect believes we can get away with a good cladding which could be stuck to the polystyrene finish with a strong adhesive. However, engineered stone is expensive and looks pastiche in my opinion. Also, the polystyrene system wrapping the whole house is expensive, so I have come up with a better solution (I think). I am thinking of building 25cm ytong block in line with the 20cm cement columns, and just applying the 5cm polystyrene against the columns to create a uniform line. I want to build wall ties into the Ytong and render over the Ytong exterior wall to seal it. I would then build a second skin of real stone on the outside, which will be held firm by the wall ties to the interior Ytong wall. This works out cheaper, as rough stone blocks are cheaper here than engineered cladding and I can build the stone skin myself slowly. I have some experience with stone and I am confident I an do the job. Can anyone see any potential pitfalls with this idea, or better suggestions ? Any advice would be appreciated.

The R-value in U.S. units of autoclaved aerated concrete (AAC) is about 1.25 per inch or 0.5 per cm. Therefore, a 20 cm thick wall would have an R-value of about R-10. Claims are made for AAC and other concrete products of an "effective" R-value much higher, but calculations that I have performed with BEopt show only a very slight thermal mass effect, on the order of a percent or two. This R-value would not meet code in the U.S., but it sounds like you might be building elsewhere (Greece?). Foam board like EPS is expensive. You could perhaps reduce costs by building an interior stud wall and filling with cellulose and covering with sheetrock.

Non-reinforced masonry is supposed to be bad in earthquake zones. Is the concrete reinforced skeleton enough?

StrayDog; all SIPS perform well in seismic ares

I would look ICFs or insulated concrete forms. They are more likely to have siezmic zone certifications.

Happily,neither Lee nor BEopt play any role whatsoever in securing a building permit for an AAC house. I got mine by clipping the AAC-4 table in this pdf to my REScheck calculation.http://www.ytong.org/images/us/rd_en/HEBEL_AAC_Product_Line.pdf From a static R9 to a mass enhanced R15 in the Washington DC climate is certainly more than a percentage point or two change. If you think Hebel (Ytong elsewhere in the world) has misapplied ORNL's work on mass effect,feel free to make your case to the FTC.

Seismic criteria for AAC design do exist, JeffD: http://www.icc-es.org/criteria/pdf_files/ac215.pdf Here is a report on how the 5,578 AAC homes in Kobe Japan fared in a 7.2 quake in 1995: http://www.hebel.co.nz/about/earthquakes.html (astoundingly well.)

As to straydog's question, I was told (by the Sider Oxydro stucco folks in the U.S.) that AAC requires mechanical fasteners for foam, tile and lick-and-stick stone, for the simple reason that its porous surface offers very little actual concrete to carry any weight. To tile bathroom walls in my house, I used 5 inch wood screws to attach Hardie backer to the blocks first and then tiled over that. The mortar joints are a different proposition. The polymer fortified mix I used is so hard that the blocks broke off adjacent to the mortar before the mortar let go. The questions then is whether the mortar web is substantial enough and what changes in the seismic design. You'd want the stone supporting itself on the foundation. Here in the US AAC folks are happy to entertain questions.