I'm curious what the experienced folks on this forum think of ICF VS strip form for wall construction. Specifically value is what I'm thinking about. An 8" thick ICF wall costs roughly $14-$15/sq. ft., which on a 9' wall equates to about $135/linear foot of wall. This is opposed to a strip form wall of the same thickness and height that might cost around $70/linear foot (rough?). Then with the strip form wall you will have to frame on the inside and add insulation, but that isn't going to add another ~$65 per linear [edit] foot to the cost!! You also don't have the insulating foam on the outside of the wall with strip forms, but that seems like more of a hassle to me than a benefit (maybe I'm wrong). Just curious if I can get all the benefits of concrete at a cheaper cost by going the strip form route. Thanks!

I think you mean $65 per linear foot or $7.22 per sqft.

Sorry....yeah I meant per linear foot. Good catch.

edit*

With strip forms you can also use liners for a better look. On the other hand, I've heard of much lower prices for ICF forms that your figures imply. On the other hand, you can't leave the ICF unfinished (inside or out).

You should know that ICF's are not meant for basement construction. They are meant for super energy efficient basement/house or whatever you have construction.

If you want a cheap R-7 basement use plywood forms and furr it out with lumber on the inside and put in some batt....

if you wanted a plywood formed basment to perform as a typical R-22 ICF basment you would have to furr it out with 2x10's and fill in the gaps with batt insulation.

or 2x12's... i really dont know...

Since there is such a difference in price between strip form concrete walls and ICF, have you considered spraying 2.8# closed cell polyurethane foam on the outside of a conventionally placed concrete wall from footer to the top of the wall? The exposed, exterior part of the wall will require protecting the spray foam. Inside the basement, just furr out the walls for thin outlet electrical boxes. 1.5" thick furring strips plus 1/2" drywall should accommodate the thin electrical boxes. Although the 2.8# closed cell foam will offer a lot of water resistance, I would still spray waterproofing on before adding the spray foam. Dana1, do you agree? This is what some spray foam installers are advocating in my area. By the way, although I use paragraphs, the formatting is lost when I hit the Submit button. Does anyone have any ideas how to correct for this lack of formatting?

BTW - I was talking about the above grade walls mostly in this case. I have already decided no matter what that strip forms are the way to go for my basement walls.

@jonr -- I didn't think about the liners, but that is a fantastic idea. I originally was thinking of brick on the outside of the home and part of using strip forms was to save money to cover the brick cost. However, the liners might be considerably cheaper and still look very nice. I suppose I need to see if the local concrete strip form folks carry the liners or what?

@Alton -- I'm not even sure if it's worth worrying about the insulation on the outside of the house. I guess that was part of my question. Are you advocating below grade, if I ended up putting a spray waterproofing coat on the outside wall, and then put the closed cell spray foam on the outside (in contact with the earth), that would be an acceptable (and lasting) installation? Then I can do what you are saying with the thin walls inside the basement and save some $$ there too. Bingo insulated basement? What about the air gap/dimple membrane around the wall? Not needed? I don't know much about closed cell insulation, but I just wouldn't want it to absorb water and hold it against my basement wall for obvious reasons :-)

As far as cost for ICF walls....I just don't think I will get 8" walls for less than $110/linear foot, period. 6" walls just seem too thin to me. The strip form guys won't even put up a 6" wall. The min is 8". So at the VERY LEAST, there is a difference of $40/linear foot I think, which on an average size house could mean a difference of about $10,000 [per floor] easily.

IMO, the big advantage of spray foam is the air sealing. Since that isn't so important with concrete, I'd use rigid foam or cellulose. You can even put rigid foam in the forms. SCIPs (concrete/foam/concrete) are another possibility.

http://www.greenstreak.com/div3/formliner/formliners.asp

http://www.specformliners.com/

OK - update on this....I got a cost estimate of an 8" strip form wall and it is actually ~$46/linear foot! Um...so yea. @jonr -- yeah I suppose you're right that I really will only need to use the spray on foam in the attic. I don't know how much that will actually save but if it gets into the $1000's then I suppose it's worth it.

Here are some form liners that hold real brick (typically has better color than concrete).

http://www.scottsystem.com/rim_snaps_specialized.html

If you have an exterior concrete wall that is exposed to the weather, do you need to seal it in any special way? I mean of course the concrete itself needs to be meant for that purpose (correct PSI and air entrained and what not) but if I used a liner for a pattern could the concrete serve as my exterior without water infiltration problems or excess wear and tear on the concrete wall?

The idea is to use the heavy 2.8# closed cell foam because it does not absorb moisture like light weight open cell and it does cure with a fairly tough skin. The source for my info is David Vaughan, Director of Engineering/Product Development with Burtin Polymer Laboratories. David wrote a book about spray foam that industry professionals reference. Warning: Check with your code official because foam is not supposed to be used below grade in heavily infested termite areas unless steps are taken to meet the code. I think the 3d (dimple) membrane is used primarily with ICF. I think that with the closed cell foam over a spray on waterproofing should suffice. This assumes that the concrete is good quality with enough cement and fly ash to make it resist water intrusion. One secret to making concrete more waterproof is to maintain the proper water to cement ratio.

@Alton - I know the IRC states that below grade foam isn't an issue if the construction is all non-combustible type of material (concrete/steel). I am in Iowa and we have termites here, but not really in the area I would build anyways. Certainly there is below grade foam for shallow frost protected footings so I guess it makes sense that you could use the stuff underground. I guess the trick would be how to spray it in and hold it near the wall and then get backfill material down in the perimeter. As far as the concrete is concerned, we just spec exterior concrete and the suppliers give us the right stuff. Although if I go this route I would probably still use the dimple membrane below grade.

@johnr -- looking at the liners, it appears they are meant for wood/plywood forms and not the reusable forms (metal/plastic?) that the concrete contractors use. Given that I am not sure how I could use liners unless I missed something while reading the sites you linked. The concrete guys told me folks tend to put stucco on the outside of exterior above-grade concrete walls. Not sure how that would be for price but I guess I'll look into it.

Posted By Baldwin2012 on 31 Aug 2011 12:25 PM
You should know that ICF's are not meant for basement construction. They are meant for super energy efficient basement/house or whatever you have construction.

If you want a cheap R-7 basement use plywood forms and furr it out with lumber on the inside and put in some batt....

if you wanted a plywood formed basment to perform as a typical R-22 ICF basment you would have to furr it out with 2x10's and fill in the gaps with batt insulation.

or 2x12's... i really dont know...

But in fact, that approach will create seasonal moisture problems in most US climates.  At the very least put some semi-permeable foam insulation between the concrete- the amount of foam necessary will depend on the local climate and whether it's above/below grade.

With a 2x10 studwall and no air gap or capillary break between the stud and the concrete, the exterior edge of the stud is going to be drawing both ground moisture or weather related moisture into the wood- it can and will rot in a variety of climates- you have to put SOMETHING in there to block that transfer.  Below grade, if that exterior element is too vapor-impermeable (or if the studwall has an interior vapor barrier), the studs will accumumlate ground moisture wicking up from the footing into the foundation wall- it needs to be able to dry through the insulation layer toward the interior. But without an interior vapor retarder the above grade portion will suffer from frost/ice/condensation on the concrete, if unimpeded.

But with sufficient R value  air-impermaeble but semi-permeable to water vapor foam located between the studs and concrete those issues can usually be avoided.

Sometimes it's heluva lot easier to just go with ICF, eh?  (I would, for R15-R20-ish foundation requirements. But above grade, it depends...)

The real fun begins when you're looking for R values in excess of R22, at which point the economics of R value purchased in the form of ICF may not always be favorable.  R22 is a pretty good wall compared to code-min for US climate zones 4 and lower, but it's hardly above code min in some more northerly climes- and not exactly super-insulated.

If you want more than R22, take a look at ICF manufacturers like Polycrete that can make variable and custom foam thicknesses. Polycrete can make foam thicknesses and core thicknesses up to 12 inches.

My understanding is that they use a specific adhesive to attach form liners to metal forms. Yes, you can definitely use concrete as an exterior finish.

Posted By jpj on 31 Aug 2011 02:36 PM
OK - update on this....I got a cost estimate of an 8" strip form wall and it is actually ~$46/linear foot! Um...so yea. @jonr -- yeah I suppose you're right that I really will only need to use the spray on foam in the attic. I don't know how much that will actually save but if it gets into the $1000's then I suppose it's worth it.

So as an example, 100' feet of 9' wall 8" thick will only cost you $4600??  I have a hard time believing this.  Does this include rebar? Concrete?  Or is this just the labor?

I assume you want to build a concrete house because of storm resistance, is this correct?  Iowa is a tornado hot-spot.

If so, I'd have to beleive ICF is the only way to go.  Here are the reasons why:

1. High insulation value
2. Furring strips built in for attachment of drywall, outlets, etc.  Strip form will require some kind of furring strip added, which would add up some serious labor costs.
3. ease of attaching just about any exterior finish, ie siding, eips, brick, stone, veneer.
4. And this is a big one, did the concrete sub quote you their price including window bucks, door bucks, plumbing, HVAC, dryer vent, ERV and any other protrusions?  When building with ICF, these become easy, because you build them in place as you go along.

These are just a few reasons I'd reconsider building an above grade house with strip forms as opposed to ICF.

Sean

Sounds like having a discussion about buying a Chevy when the guy already bought a Ford