Hello everyone. I'm embarking on designing and building an ICF house. My lot is long and skinny (1:4 rectangle) so I'm looking to build a 26'x50' rectangular 3-story structure (really a "2.5"-story structure) 30' tall with an additional 1.5' parapet atop a flat roof. I'm looking to use either Nudura or BuildBlock. What I need is a clue. I don't want to spend the time and money to design and engineer a structure only to discover that it's going to cost $500k to pour. After a week of searching these forums and three weeks of reading all of the posts in linear fashion like a book (I'm about 2/3rds of the way through), I'm starting to get an idea about many aspects of the project, but the one thing I haven't found is any general reference to the thickness of the block required to build a crackerbox with 31.5' tall walls supporting two floors and a roof (preferably all concrete). Now I know that ultimately I can only build what my engineer says I can build, but I'd like to have a ballpark idea of what that's going to be. Right now I have no idea whether it's possible to build with 6" walls or I'm going to have to resort to 12" forms or larger. Okay, so I guess essentially I'm trying to figure out how not to bring the engineer something that turns out to be ridiculous, but I really would like three stories. I found out while building a garage apartment on the adjacent property that at 20' foot or so up off of grade I've got a beautiful vista view of downtown Austin over my back yard. I really want that view. Still, the wife's not getting any friendlier and the kids aren't getting any smaller, so if I have to forego three stories, I need to know now =8^] yours/ peter.

Hi Revolver65:

Good decision to go with ICF construction. So what is open now is whether you will have a two-story building or a three-story building, and what type of block you are going to use.

What thickness walls will be required will depend on the structural arrangement -- that would determine the loading on the walls. Unless you end up with a design that calls for unusually large spans, I don't think you would need a panel wall of more than 8" thick even at the lower level -- it is quite possible that you might be able to do with even a 6" wall throughout.

Your wall contractor may have his own preference for the type of block that he may want to use -- who knows he may even have preference for a screen-grid or a waffle type profile. After the concrete pour, when the walls are all done, construction with any ICF wall will have essentially the same beneficial features.

Good Luck with your project.

I agree with the 6" core wall units as that is what I typically use for my 2 storey designs, which average about 30" +/-. Another path you could take is to review whatever current code you build under. For example, we now use the IRC2003 which has simplistic but realistic code sections for both above grade walls and foundations. That is a good starting point!

Gentlemen!

Thank you for your kind and informative responses. It's exactly what I needed: a glimpse of the contours of what is possible.

yours/
peter.

Peter,
We are doing an elevated three story that is 8', 6", 6" and 4".
We are also doing a 6", 6" and a 4"
The 4" walls I do not recommend to DIY's although I have helped a couple through the process.
The two inch set back at each floor makes it easier to set the floors on. I recommend Insuldeck.
Your engineer can get up to 200 MPH wind load capability with 60 grade #4s at 16" horz and #5s vertically at 24".
Hope this helps.
Regards,
Joe

Peter,
You can build up to 4 stories with a with floor and roof all concrete on a 6" wall.
The price might be around $26 per sq. floor ,per floor -for just the 4 story concrete box .
The wind loads wind loads will be out of this world if you also use icf interior walls.
I hope this helps you get an idea what is possible to do .

Well all I can say is *damn* reinforced concrete is strong. Fortunately I don't have any seismic requirements to deal with here, nor hurricane codes or frost cycles. The only thing I have to contend with is high-clay soil and that's all going to be mitigated in the slab.Other than that, my biggest issue with the authorities is going to be over building right up to our draconian new "MacMansion" maximum height limitations.

I've been trying to "design in" as much efficiency as possible because although it hasn't gotten to California levels here in Austin, construction is still booming big time here. So I have no interior ICF walls at this point and all of my floor spans will be 24' or less as that seems to be where the point of diminishing returns really starts to kick in with concrete decking. I'm going to easily wind up paying $100/yard for <.5" aggregate mix, and if Vertiforce or something else like that is added then we're talking $130-150/yard. As efficient as my design will be to stack and buck, three stories with concrete floors means an unavoidably high number of pours and pump fees. Still, if what you gentlemen indicate is even half-way close to the mark, I can put this house up with no compromises. I can't tell you how gratifying that is to me. Thank you all.

yours/
peter.

Just remember, last time I checked, Vertiforce does not replace rebar below grade, nor does it replace lintel reinforcing!

Here's what we have found with multi story structures. To keep your cost as low as possible ..... use less material..... A super strong light weight structure if you will. By reducing weight you reduce foundation requirements. You might even be able to use a frost protected shallow foundation without any footings. Above grade you could use a 5" icf wall, reducing weight and reinforicing. you can use a concrete floor that uses only 3" on standard concrete,and still meet your spans. Use this floor system for a concrete cap and put a standard truss roof above. Although I love our Plug and Play radiant floors, I would for go the radiant and use a 3" concrete floor to save weight and money. 1/2" rebar will fall around a 16" grid. All this is very inexpensive to engineer as we use simple span charts . Before you actually design this home, get some qoutes on what you want. And then you will know where you stand on cost.