Naive question about ICF

jamnich314December 28, 2012

Before browsing this site for the past year or so I had never heard of ICF. Now, I hear about it and see lots of build update pictures with ICF walls.

Can somebody give me the low-down on ICF walls as opposed to generic wooden walls? Are they more energy efficient? Are they more expensive to build? How they are they compared to 2x4 or 2x8 wooden walls? Are most ICF walls exterior only or exterior and interior?

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Those are great questions! First, ICFs are used only for exterior walls. They will usually far outperform most stick built walls, meaning they are stronger, more comfortable and energy efficient.

Generally, ICFs are usually used in below grade applications (basements) but are increasingly used above grade. Their big drawback is upfront costs which can vary a lot. The labor costs are the killer and I would say they are one of the more expensive ways to build a high performance wall.

Pre-cast concrete panels (where available) in my opinion is a much better option than ICFs. They have many of the same attributes of ICFs yet are almost always cheaper, include engineered stamps, more airtight and water resistant, better warranty, and are installed in hours instead of weeks. They usually have the concrete on the outside which may affect the energy performance slightly but its worth it by having an already finished surface or one that will more readily take paint or stucco.

Again, pre-cast concrete panels are usually used below grade but some are finding that it works great above grade as well. My personal favorite wall system above grade is SIPS and Iam sure others will chime in with their opinions. There are many ways to build high-performance walls but remember that the roof and floor are just as important to detail correctly.

Here is a link that might be useful: Building Science; envelopes, SIPS

    Bookmark   December 28, 2012 at 11:46AM
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Let me guess BrianKnight, you happen to know someone who sells Pre-cast concrete panels?

    Bookmark   December 28, 2012 at 1:27PM
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I like ICF a lot more than wood because it's dimensionally stable and cannot rot.
One flashing failure can mean disaster in a wood framed house while with ICF it may not even register, let alone do any damage.

Reinforced concrete is also magnitudes stronger than wood and easier to get airtight, which together with an Energy Recovery Ventilation system can get you an efficient house fairly easy.

I would also build interior walls out of concrete because it makes the house feel extremely solid, not hollow like studs + drywall.

    Bookmark   December 28, 2012 at 2:01PM
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How would you deal with electrical, plumbing and HVAC with concrete walls though? With wooden studs you fit everything between the studs but that doesn't seem possible with concrete.

    Bookmark   December 28, 2012 at 2:17PM
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The concrete is on the inside of styrofoam blocks. The wires go in channels you would cut into the foam.

    Bookmark   December 28, 2012 at 2:26PM
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I embedded conduit and plumbing pipes/tubes inside the concrete (I have insulation on the outside only so that the thermal mass effect is higher on the inside)

    Bookmark   December 28, 2012 at 3:10PM
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ICF is also fire "proof"/resistant whereas stick frame, obviously, is not.

My uncle built with it about 20 yrs ago now (!), and still loves the house. It was relatively new back then. It was pretty DIY friendly and yeah, wires, etc really aren't an issue. You DO want to really plan out your design. It is more difficult to get windows cut in later, for example...

    Bookmark   December 28, 2012 at 3:17PM
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Jamnich - Read this blog:

They are building a house with ICF and the details may help you.

We're planning a build with ICF because it's thermal mass inside the insulation and far tighter than studs.

You do have to plan REALLY REALLY well for all the things that pass through the walls, like windows and doors, and where you plan to have conduit for wire runs, because it's gonna be rebar and concrete outer walls.

It might be more expensive to build (I've seen estimates of 10% higher), but you will get a break on insurance (basically fire-proof) and the heating and cooling costs are lower if you do it right.

    Bookmark   December 28, 2012 at 4:21PM
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One thing that's hard to put a number on is the the huge amount of thermal mass in an ICF (or any concrete) home. Changes in outside temperature can take days to affect ICF, even with no heat on. The houses I've been in also seem to have a very consistent temperature throughout.

It may not be important to you, but ICF also makes a very quiet house as well.

I'm currently building my own ICF home, and it has so far been a fun project. It will be the first fully insulated house I've lived in in my 59 years.

    Bookmark   December 28, 2012 at 4:27PM
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@ millworkman: I do know a salesman and he's pretty good and very busy unlike the ICF sales guy I knew who has had to switch careers last I heard. Maybe I shouldnt be informing people of more affordable options (that perform equally or better) because that means I make less on my cost-plus projects. So if any client wants to use ICFs, by all means lets do it!

@jrldh: With your flashing reasoning, we should be building concrete roofs and floor systems too. I feel ICF windows are more difficult to properly flash, its hard enough to get conventional methods flashed correctly.

Stonger I agree with, or as strong as other concrete methods (pre-cast,poured) but thats just the walls. Roofs become the weak link quickly when strengthening walls. Not airtight though, there are much easier ways to get airtight if thats the goal, and it should be! Airtight is the most cost-effective way to energy efficiency in most climates.

Very interested in how you eliminated the interior foam? Why not do traditional poured walls and add the foam sheathing? Related to this..

@ lazy gardens and flgargoyle; According to the best known studies done from below link, ICFS benefit very little from their thermal mass. Removing the interior foam however would probably effect that science a lot.

@everyone; ICFS foam, usually styrene is quite flammable. You would need to build the entire structure (interior walls, floor, roof) of steel and concrete for any meausurable fire resistance outside of sprinklers. Most high performance walls are going to be very quiet. I would put that extra ICF cost into nicer, triple pane windows which would probably have a more rounded benefit, especially in heating climates. Oh, and in case millworkman is wondering, I know a guy..

Here is a link that might be useful: Oak Ridge National Labs Thermal Mass/ICF benefits study

    Bookmark   December 28, 2012 at 9:08PM
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About flashing and my reasoning: yes, the floors (it's three levels) and roof of my house are concrete. There is no wood in my house's structure.
I use tape flashing that conforms to German RAL guidelines and should it fail, the EPS and concrete gets wet without any fear of a rotting structure.

I used standard concrete forms without insulation for interior walls.

    Bookmark   December 29, 2012 at 8:58AM
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