Ok, I gotta do due diligence by researching all my building options, so I'm looking at ICF's as a DIY project for a two story house. I've read that building codes (don't have any where I'm building, but I want to use common sense) require 10" thickness for traditional basement walls that exceed 8' in height. If ICF's are used from the footing up to the roof line of a two story walk-out, would the thickness be the same all the way up? Is the code really about the height of the total wall, or the height of the backfill pushing against a basement wall? My "walk-out" floor plan is really less basement and far more two story: I'm just planning on pushing the back wall into a low hillside and earth-berming the back width of the house (think storm shelter with concrete ceiling stretched full width. I'm wanting 9' ceilings for both floors. Would 8" ICF blocks all around suffice?

I'm not sure where you got your code requirement for 10" below grade, but 8" poured concrete walls are used all of the time for basements. You can easily do 2 stories above grade with 6" core ICF. The local Fairfield Inn is 4 stories - all built with 6" core LiteForm ICF.

I'm not a big fan of rules of thumb, but 1" thickness for every 1' below ground level is often used to ball park. So if you had a 10' below ground basement, you might use 10" thickness from footing to ground level, then 8" thickness to second level, and then 6" for second level. Besides the wall thickness, the rebar schedule must also be determined. Again, there are many design factors (seismic, wind loading, etc.) that must be considered and properly addressed. Some building codes are prescriptive (i.e., just based on materials and construction method used) and other building codes are performance (i.e., based on design performance criteria and requiring structural engineer buyoff of materials and construction method used).

6" ICF concrete cores are the norm and many 2+ story ICF walls with 6" concrete cores have been built. Some do 8" concrete cores but for 90% of projects the 6" core is plenty strong. Some claim that even 4" cores are doable but I don't see 4" cores that often. I believe consolidating a 4" core with rebar is difficult. In the concrete world, 4" is the bare minimum for structural concrete. The same goes with slabs, 4" is the bare minimum for a slab.

With that being said, a 6" core will more than work but an engineer will be needed to engineer the project.

Posted By Lbear on 18 Apr 2013 01:03 AM

With that being said, a 6" core will more than work but an engineer will be needed to engineer the project.

Not if your home falls within the design bounds of HUDs prescriptive method for ICF construction as generally adopted by the International Residential Code, unless your local building code has some special quirks.

When comparing traditional basement walls to ICF, please remember that most cip walls had very little if any bar in them.
You can get your strength from just thick sections of concrete or from concrete AND bar. Buried walls have much more lateral pressure then above ground walls. This pressure is a combination of burial depth, soil types, soil saturation and frost.
People who arbitrarily say 6 " is enough are going to get someone killed. Yes you need to go with an engineer if you don't understand concrete or you have to know what you are talking about.

AAC-curious,

Since your home will be a two-storey above basement, you should give some thought as to how the main and second floors are supported by the concrete ICF walls.  Although the floors will act as a diaphragm brace for the walls, the manner of connection can be important for cost and safety.  Various ways to connect the floors to the walls.  Some ways are stronger than others and less costly than others.  It might not hurt to ask for opinions as to what would be best for your home.

I have some walls higher than 23' which include 11' below ground, full basement burial and yet an additional floor on top that are engineered to near maximum seismic resistance. They are all 6" walls. Note that I said "engineered".

"Engineered" is better provided that the engineer is good...and you will eventually find out.

Posted By sailawayrb on 19 Apr 2013 01:24 PM
"Engineered" is better provided that the engineer is good...and you will eventually find out.

A lot of engineers don't know ICF or InsulDeck. In turn they learn on your project and your dime. They usually go overkill on a lot of stuff and make some incorrect choices, simply based on the fact that they never engineered such a product. Not that the choices would cause structural problems but the choices don't transition properly into the field, that is when the ICF GC is usually caught in the middle.

ICF is just reinforced concrete. It is hard to imagine that someone who hangs out his shingle for construction engineering doesn't have experience with that.

Posted By ICFHybrid on 19 Apr 2013 07:49 PM
ICF is just reinforced concrete. It is hard to imagine that someone who hangs out his shingle for construction engineering doesn't have experience with that.

You would think.  It's reinforced concrete with stay-in-place forms. Yet when I spoke to some engineers, they were very apprehensive about approaching ICF and that means they have to read and study up on it prior to doing anything. This means higher $$$ when it comes to engineering.

With InsulDeck, they were just as lost. They did not know that it was a stay-in-place concrete form that incorporates I-Beams for it's strength.

Safest bet is to use an engineer who knows ICF and InsulDeck (if you are using that form). It will be less headaches and cost less $$ in the long run.

With that being said, the bids I got from engineers who knew ICF were all over the board. Some were as low as $1.50 per sqft to as high as $4.00 per sqft. The higher bids were engineers who were busy and weren't looking for work but would take the project it if the price was right.

The assumption that the unknown causes higher prices does not bear out in the construction industry as a rule. I think most GC will agree that most of the jobs they lost went to bidders that didn't know what they were doing or missed something important. And the owner will almost always take the low bid regardless. I would much rather bid against a knowledgable competitor then someone who doesn't know what they are doing.
I agree with ICFHybrid - Engineers just calculate compression and tension, what's around them doesn't matter. When a P.Eng. looks at an ICF wall they simple say, "so you want me to replace 2" of concrete with enough rebar so you can go from an 8" wall to a 6" wall." Okay that easy. Everything else stays the same as a CIP wall." When the look a insulDeck or their equal, the engineer has the add complicity of supporting the wet concrete during the pour. Still nothing they haven't done many times with suspended slabs. It would be very seldom that an increase in fees is due to the foam.
So in the end the safest bet is to use an engineer who is open and willing to communicate with you. If he is willing to listen to what you want, you will probably have a successful project.

I'm certainly not an engineer, but some years back I got to listen in on an earthquake symposium full of civil engineers. In between all the interesting discussion about soil liquifaction, I think I remember someone saying structures ought to get lighter as they go up--less inertia to overcome. That would imply that a basement ought to be thick, the first floor not-so-thick, and the second floor thinner.

I've got only one wall embedded in a hill, with backfill 8'6" from footing--and I'm really starting to reconsider that height, given it mandates a long retaining wall. The natural slope of the site is only about a 4' drop, and I'm starting to reconsider a crawlspace (genuine oak floor that I get to stain my color instead of engineered stuff that has to float...).

Would 8" ICFs in the earth-bermed storm shelter + 6" ICFs for the rest of the first floor sound reasonable? What about 4" ICF's for the second floor in order to go along with the engineering principle mentioned above? Also, do wood joist floor/ceiling systems behave as diaphrams to transfer lateral loads? Do internal stick-built walls at 90 degrees resist wind loads?

Posted By AAC-curious on 19 Apr 2013 10:46 PM
I'm certainly not an engineer, but some years back I got to listen in on an earthquake symposium full of civil engineers. In between all the interesting discussion about soil liquifaction, I think I remember someone saying structures ought to get lighter as they go up--less inertia to overcome. That would imply that a basement ought to be thick, the first floor not-so-thick, and the second floor thinner.

I've got only one wall embedded in a hill, with backfill 8'6" from footing--and I'm really starting to reconsider that height, given it mandates a long retaining wall. The natural slope of the site is only about a 4' drop, and I'm starting to reconsider a crawlspace (genuine oak floor that I get to stain my color instead of engineered stuff that has to float...).

Would 8" ICFs in the earth-bermed storm shelter + 6" ICFs for the rest of the first floor sound reasonable? What about 4" ICF's for the second floor in order to go along with the engineering principle mentioned above? Also, do wood joist floor/ceiling systems behave as diaphrams to transfer lateral loads? Do internal stick-built walls at 90 degrees resist wind loads?

Earthquakes can be complex as there the shakers, the swayers, and the bouncers (of course those are not scientific terms but just terms for different forms of ground movement). A 6" ICF wall is about 4x stronger than a 2x6 wall (8" oc) that is double sheared on both sides with 5/8" OSB, when it comes to lateral forces.

Soil liquefaction is an interesting phenomena. There was land for sale that the sellers were boasting (and still do to this day) on how shallow the water table was to the surface. It's basically 20-30 feet below grade. People view this as a great selling/buying point they don't have to drill the well that deep. Quite the opposite is true in a seismic zone. During an earthquake the water will actually rise to the surface and the entire foundation will buckle and collapse. This was seen in the recent New Zealand quake and elsewhere. People built homes on that land and one day they will unfortunately pay the price, hopefully not with their lives. The area is rated Seismic Category C with a 7.0 potential.

I prefer to have my house sitting on ground that the water table is 250-300 feet deep, no worries about soil liquefaction taking place. One would probably be safe at around a 50-75 foot water depth table but I would say 100 feet is my safe zone.

structures ought to get lighter as they go up

Proper engineering dictates that the structures are as light or as heavy as they need to be and not any more or less.

Also, do wood joist floor/ceiling systems behave as diaphrams to transfer lateral loads?

Yes, but they are not the same as a concrete joist floor/ceiling system. And, as your seismic resistance needs go up, the connectors between the foundations and walls become much more important.

Do internal stick-built walls at 90 degrees resist wind loads?

Yes, but not the same as concrete walls. Typically, shear walls are sheathed with a greatly increased number of both standard fasteners (nails) and engineered connectors of various types.

Posted By ICFHybrid on 19 Apr 2013 07:49 PM
ICF is just reinforced concrete. It is hard to imagine that someone who hangs out his shingle for construction engineering doesn't have experience with that.

This is a true statement enforced by state licensing requirements and the law...

A structural engineer doesn't typically need to know what specific brand of ICF will be used. The structural engineer only needs to know the type of form (e.g., solid core or waffle) and the building design conditions to allow determination of the proper wall thickness and the rebar schedule (or Helix mix).

GCs only get caught in the middle when they neglected to consider design conditions during the bid process and end up winning the contract likely because of a low ball bid... A good GC will eat the expense and learn from their mistake. A less than good GC will bad mouth the engineer (and often the building codes and the inspectors too) and try to con the customer to retain their profit. This is why there are building codes and inspectors. In good states, there are also state contractor construction boards that require contractors to be licensed, bonded, and insured, and are whom are fully empowered to step in to make things right between the contractor and the customer when necessary with zero cost to customer.

We are in the process of completing a two story (in ground 14') total ICF home in rural mid-south... We have used 8" concrete with 6.5" of foam blocks. We also used #5 Rebar every 16" vertical and horizontal... before starting the first course of ICF blocks, we poured a 24"x 30" wide footing over insulated base on gravel. The three walls in the ground are supported well... back wall is over 14' in the ground and there are two "deadmen"- 8'x12'x3' to support the back wall for backfill. Drainage is very important. This is not a beginner project, it takes engineering and the cost is approximately $245. per square foot in our case... ( 11' ceilings, 8'x12' doors,skylights across the backside, 12 volt LED lighting system to a solar panel and battery storage,hydronic heat in floors, etc... Good Luck to you. It takes time ,thought, and the patience of Jobe...