ICF General Design Guidance 2

[eng003]

Looking to get into ICF construction design; looking for any recommendations on good books, design guides, websites/organizations for design & detailing. Also interested in any advice in this area i.e. pro's/con's, pitfalls, etc. Thank you

 

[dik]

There are a couple of soft cover design guides, one technical the other prescribed constrution. I think they are by the Portland Cement Association. I don't have the titles here, but they are at the office... I'll dig them up tomorrow.

Dik

 

[msquared48]

Be wary of untested, yot manufacturer rated ICF products. Salesmen will tell you anything...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dik]

The publications are:

Structural Design of Insulating Concrete Form Walls in Residential Construction, and

Prescriptive Method for Insulating Concrete Forms in Residential Construction

They are published by NAHB Research Centre, Inc. Upper Marlboro Maryland.

Dik

 

[shobroco]

For some reason, no one seems to remember that ICFs are Insulated Concrete Forms. That's all they are: forms. Your structural design is of the concrete walls hidden inside the styrofoam skins; the styrofoam does not contribute anything to the structure. The design is no different than any other concrete design, unless you are looking at design of formwork. In that case, use the information from the ICF manufacturer for rates of pour, height of pours, bracing, etc.

 

[TXStructural]

PCA is in the process of revising the Prescriptive Methods book as I type. If you are designing residential and similar low-rise, it is the most economical way to design if you are not equipped to do full analysis. The prescriptive method book has been passed between PCA, NAHB, and FHA, but now is a consensus document published by PCA:
In PDF:

http://members.cement.org/EBiz50/ProductCatalog/Product.aspx?ID=320

or print:

http://members.cement.org/EBiz50/ProductCatalog/Product.aspx?ID=319

ACI 560 is looking to have their design guide ready for public comment by Spring 2013. We will have training sessions once that is in print. ACI 560 will also have sessions at next fall's ACI convention in Phoenix.

http://www.cement.org/homes/

As far as pitfalls, the main one is trying to construct these without having proper training. Most manufacturers offer training at low or no cost. My first ICF course was as a builder and designer about 12 years ago, from ARXX. Each ICF brand has its quirks and tricks, so best to pick one to start and stick with it until you understand it thoroughly. That said, I have chastised several ICF industry representatives for proclaiming the differences in using their product. With flat wall ICFs, there are differences, and attending to these in the design phase will improve economy, but ignoring them with an experienced builder on the project is not a real problem. The biggest issue is to find out before design which system you plan to use, so you account for block sizes and things like foam thickness. Otherwise, you may end up with inefficient use of ICF blocks (like having to cut 8 inches off the height) or need to revise cladding and other details (particularly around windows and doors.)

Contact local contractors (look on manufacturer's website for these) and identify one or two brands and builders. Then, get familiar with the mfg design instructions, which cover things like block sizes, coursing, corners, and concrete and foam thickness. Stick with flat wall systems for now. The waffle and screen grid systems are more complicated for design and construction, and the amount of concrete you will save is usually of little importance on most small buildings, everything else considered. Don't be afraid to use more reinforcement (what did you expect me to say) located in the middle of the block. Don't over economize concrete and steel when doing so complicates the layout or design. The formwork is the place to economize. Also, keep in mind that the cost of conventional concrete building frames is 50% formwork (including labor), and about half of the remaining portion is labor. ICF's shift that equation toward less labor, since setting forms and placing reinforcement is much easier and faster.

 

[ddcpe]

shobroco is mostly correct except in the case of ICF's like Rastra. In that case the forms create a lattice type structure but in essence the foam is still just a form and can be ignored in terms of section capacity.

 

[msquared48]

I would have to take a strong exception to that considering some of the ICF wall sections I have seen.

If the wall just has horizontal form ties between the foam forms - no problems with the analysis both for bearing, bending and shear.

However, if the wall section is a honeycomb structure, approaching a Vierendiel (sp... sorry) truss configuration, as a couple I have seen, the analysis is not so straight forward, mostly in shear. In this circumstance, I had to be conservative and use an unreinforced concrete section for shear as there is really no shear reinforcing in the wall. A tested wall would probably have given much greater shear capacity.

It is also an interesting fact here that between the honeycombs, the form material has to permanently span between the vertical nd horizintal concrete sections to resist any lateral soil loads, and the form material, as previously mentioned, is NOT a recognized structural material, in either the IRC or IBC. Go figure...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[oldrunner]

Our local building appeals board rejected one of the systems (I think the one that Shobroco was discussing) because it didn't have a ICBO approval. We did one large building design with the Arxx system. Remember that foam has to be detail removed at intersections of the walls. Basically just considered the structure as reinforced concrete and be careful about the connections.

Did two designs: The first was in reinforced mud! There are actually some pretty good designs and construction of these structures in the old Zone 4 areas. The execution of the project really depended upon the specialty contractor. But he decided to go to Africa and we did the project again with the Arxx system.

I like the old W-Panels (or Impact or Insteel or wire mesh welded cages with an inch of foam and 7/8" of high strength stucco on each side) Our firm first came across these in Nigeria but found out that they were being manufactured in Chino, California. Apparently you could design them as folded plates and span long distances or, we understand, they were used on high walls on a project in Saudi Arabia, providing the folding design with the panels about three inches thick. Very easy to install and we used plastering pumps instead of shotcrete.

 

[shobroco]

ddcpe & MM: Sorry, my comment seems off base because I've seen lots of different systems but never one of the "honeycomb" ones. ICF has become pretty popular around here but every system that anyone uses here, including floor systems, have simply been forms that remain in place as insulation. I'm sure if the wall/slab ends up perforated with styrofoam infill, it makes a lot of difference & requires a different approach.

 

[concretemasonry]

shobroco -

Some of the earlier systems had block with foam exterior faces and some portions that formed partial height webs, so the block was an total rigid foam block made from EPS foam.

The volume and bulk of the block including the voids made shipping costly and pests/vermin could tunnel through the foam connection portions eventually.

Since then, the flat plate faced systems with different type ties of varying lengths (for different wall thicknesses) have become more common and are more popular as long as they are braced adequately to prevent "blow-outs" when placing the concrete. The use of pumps to economically pour an entire foundation in lifts over time to decrease pressures, shifting and deflecting around openings or at corners.

Someday, they will universally use more the rigid and better insulation available with XPS foam.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[spats]

I remember when I first got into ICF design, there was a document produced by SBCCI (Southern Building Code Congress International) entitled "Standard For Hurricane Resistant Residential Construction". It was a prescriptive standard that the Standard Building Code allowed you to use for actual design, in lieu of running numbers. There was a table in the Standard for vertical reinforcement in above-grade walls. According to the table, for a two-story house, walls 10' high and 110 mph wind, the prescribed vertical reinforcing was #4@96" on center! When I saw that, it kind of turned me off to the whole idea, and it was years before I would ever take the system seriously.

 

[spats]

Forgot to mention... the walls had to be at least 5.5" thick.