Special Exceptions for Insulated Concrete Form (ICF) Walls 3

[KootK]

In my area (Canada), the contractors who do ICF construction don't seem to feel that they are beholden to comply with the standards that govern conventional concrete construction. This seems to include:

1) Maximum wall slenderness ratios.
2) Wall out of plumb tolerances.
3) Rebar placement tolerances.
4) Minimum reinforcing ratios.

They're so adamant about it that I'm starting to wonder if it's me that's crazy. To that end: are there any "special" standards out there that govern the design and/or construction of ICF that may permit a relaxation of the rules of the road that apply to conventional concrete?

I would post some photos and be more specific with regard to project details. However, the nature of my work on this right now is of a rather delicate nature. Confidentiality is a big deal. I appreciate any advice available. So far, my impression of ICF is that it's mostly just sketchy concrete hidden behind some insulation.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MrHershey]

None that I'm aware of. If you look in the UFGS (US military specs), the ICF section sends you to ACI documents for all tolerances and design aspects.

Also reviewing recommended specifications from one of the suppliers in the US I've worked with, the very first line in their system description:
Provide insulating concrete form product which has been manufactured and installed to withstand concrete placement loads without defects, damage, or failure and such that the cast-in-place concrete wall is designed according to ACI 318 “Building Code Requirements for Reinforced Concrete.”

They then go on to reference other standard spec sections for both concrete and rebar (and placement, tolerances, consolidation, etc.)

Main advise based on past projects:
- I'd stick to 8" or thicker to help avoid consolidation issues. Haven't seen or heard of many issues in 8 inch walls. Have seen and heard of a lot of issues in 6 inch and thinner. (edit to clarify: that's 8 inches of concrete thickness, not including the insulation)
- If you're working with a contractor who has already selected a supplier, stick to their block module for wall lengths, opening sizes, and rebar spacing. Just like CMU, they've got internal ties functioning as webs to hold the two faces together. If you specify rebar spacing that doesn't match their block module then it could complicate placement.
- Pay attention to detailing for lintels/headers. If you've got horizontal lintel bars, would recommend stacking them rather than placing them side by side. Didn't think of this and they got placed side by side on one job and formed a really effective dam.
- If your window and door frames/bucks aren't cast-in, you'll have an opportunity to verify proper consolidation at windows and doors when the forming blockouts are removed. Generally these have tended to be the worst locations for consolidation for me.
- Higher slump mix is your friend. Would work with the ICF manufacturer on this to make sure it doesn't exceed the form pressures they can handle. Despite what the contractor says, you can always increase the bracing frequency, too.
- If you or anyone else is nervous, there's nothing stopping you from setting up a special QC/SI program. In the past we've set up grids where they had to penetrate the insulation with a straight tool (awl/screwdriver) at a regular interval to try and locate voids, say 1ft x 1ft or 2ft x 2ft. Can also selectively remove and reapply insulation if you've got specific spots you're worried about. Believe I've also seem them try to do thermal imaging as the concrete is curing, but didn't work too well because the insulation tended to mask things (duh). That was in a tropical region though, may have more luck in Canada where you have a bit more contrast.

Late edit: Also just remembered that ACI recently came out with a formal report/document on ICF that may be worth a read: Link

 

[TehMightyEngineer]

When I've done an ICF structure it's been 100% the same design as normal cast-in-place concrete. Only thing you're changing is the formwork. We were very cautious about our pour due to the fact that the concrete gets hidden. If anything ICF designs should be more conservative due to the inability to do post-pour inspections.

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American Concrete Industries

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[JAE]

Agree with others - ICF is a form system - not a structural system.

Is this a case of ICF use with small residential vs. larger commercial/industrial?



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[atrizzy]

I have done ICF and, as above, have treated it as formwork alone. The issue I ran into is the required offsets if the walls are supporting wood framed walls above. The outsides need to align and you have a condition where your wall studs are loaded eccentrically and sill plates bear on the concrete only partially.

I'm not a fan...

 

[msquared48]

JAE:

Not entirely true IF the wall system has been tested and rated by a reputable and recognized testing agency.

Most out there have not though from my experience. You need to ask for the certified testing agency data, and if they cannot provide it, you have two choices... Either do the math, or run. Most cannot provide adequate backup to their claims.

Cannot name names here, but there are some that do comply. One or two?

Koot's #1 and #4 can be justified beyond code through testing, but #2 and #3 cannot.



Mike McCann, PE, SE (WA)

 

[JAE]

Mike, I'm not sure I'm following you.
The insulated concrete form system is simply a foam contraption that forms concrete and has no structural properties beyond that, right?

So if I fill that foam form system with concrete and rebar, what I'm creating is simply a cast-in-place reinforced concrete wall - i.e. designed and detailed to correspond with the local applicable building code - i.e. in my area the ACI 318.



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[msquared48]

Yes, of course the foam only is for forming and a degree of insulation.

But some of these systems have allowable loads for the concrete filled condition that have been lab tested and rated. Some by their concrete pattern infill properties are harder to justify under load than others without testing. That's all I'm saying.

Some contractors do think these systems are ok structurally to use without the use of rated tables or calculations to save money based on the word of a rep, and that is where the problem lies.

I am not disagreeing with you, just stating what I have seen.

Mike McCann, PE, SE (WA)

 

[KootK]

Thanks, all, for the feedback.

Is this a case of ICF use with small residential vs. larger commercial/industrial?

Small scale mixed use.

Koot's #1 and #4 can be justified beyond code through testing, but #2 and #3 cannot.

I'm curious about #4, the minimum reinforcing ratios. When those are justified through testing, what is one testing for? In all honesty, I'm not clear on exactly what the code intent is for minimum wall reinforcing. Minimum flexural capacity? Temperature and shrinkage? General integrity? It's not as though it's impossible to have plain concrete walls.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

And as it turns out, there's a number five:

5) Relaxation of cold weather concreting requirements.

The contractors seem to feel that, because of the insulation (I in ICF), cold weather concreting requirements can be relaxed. On a purely rational basis, I'd be inclined to agree. That said, baring any proprietary testing, I'm not sure that there's a code "out" for this. Anybody got any thoughts on that aspect?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JAE]

The tops of walls and the window block-outs are no different than any other wall placement (in terms of cold-weather) I think.

Our firm, some years ago, provided all the engineering design guidance for a major ICF producer - helping them create design tables for their manuals and all of our work was basically focused on using ACI 318 to generate tables...no testing at all.

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[DETstru]

I've always considered it just formwork.

ACI has a report on construction with ICF:

https://www.concrete.org/Portals/0/Files/PDF/Previews/560R-16_preview.pdf

Not sure if there is design info in there. I don't own it (the link is to the "preview").

 

[jayrod12]

Regarding the cold weather concreting we've made them install thermo couples in he concrete and they've been required to provide heating when the temp drops too low, but they are a significant improvement over just tarps are heat in that regard.

 

[KootK]

Thanks Jayrod. I suppose that I should have mentioned that the floor system is a sort of ICF too. Essentially pan joists with the pans incorporating permanent insulation. Primarily, it's the floor system that is of concern with respect to the cold weather concreting.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Check out the clip from the supplier catalog below. It seems that neither the horizontal nor vertical reinforcement is required to meet code minimums in their opinion.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

From a design wizard on another supplier's website. Hard not to find the one minute business a little insulting.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

To play devils advocate, the foam used in the ICF project we had was really high density (it actually might have been Nudura, can't remember what the final supplier selection was now). If you stuck a large nail it in then you're not getting that nail out without taking foam with it. I wouldn't be surprised if there was some durability effect similar to poly fiber reinforced concrete, the foam bonded to the concrete should at least have some minor benefit. Also, the foam would provide an excellent vapor barrier and thus I feel that you could rationalize some reduction in minimum reinforcement if that minimum reinforcement was for durability, appearance, or environmental conditions.

Now, away from devils advocate, that one minute thing is a little silly.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

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