The home I bought has exterior walls made of ICF (insulated concrete form). I don't know the brand or type, I just know that somehow the builders attached the drywall to the styrofoam/concrete.

I'm looking to add picture molding and want to ensure it will be secure when hanging weighty items.

I've tried a new stud finder and it doesn't work.

I was under the house the other day and saw the bottom (2") edge of the styrofoam and could not find any change in the styrofoam in the horizontal direction. I'd expected an embedded strip of something more durable than styrofoam.

5 Answers 5


I'm not an expert, but it sounds like you have what we have at our house, so I'll say what I know (and/or can reference).

From Wikipedia: "The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The forms lock together somewhat like Lego bricks and serve to create a form for the structural walls or floors of a building."

In other words, no wooden studs. Just plain ol' styrofoam.

If you're able to look at the top part of the wall, you might actually be able to see the protruding Lego brick-like top part of the interlocking structure. This would also tell you just how thick the form is.

While Wikipedia says the form bricks are dry-stacked, it wouldn't surprise me if there were a little adhesive used between them (it kind of seems like a good idea, but it's possible the form manufacturers recommend against that for some reason).

As far as how they attached the drywall: just a bunch of screws, in our case. It's also reasonable to use adhesive in addition, as long as it won't eat through the styrofoam (or other material), of course. The styrofoam was actually surprisingly strong when I was drilling screws into it. Given that they used somewhere in the neighborhood of 20 screws on the 4' wide floor-to-ceiling sheet of drywall, I have no concerns about it coming down.

There are electrical outlets and phone jacks on our ICF walls, and the lines and boxes are accommodated by carving out appropriate cavities. That creates another factor to consider when drilling into the ICF wall. Specifically: how straight are the channels that were carved out, and in which direction were they carved? Did they use nail plates along the route?

Now, as far as attaching things to the wall securely is concerned... I doubt it would be equivalent to a stud in terms of support capacity, and I'm having trouble finding information on this topic online. If the drywall is attached directly to the ICF, you won't have any cavity behind the wall to place a spreading-type anchor, so those are ruled out. Of course, if you make the assumption that the wall is at least as strong as drywall on its own (indeed, I'd assume it's at least a little stronger), you can use a self-drilling drywall anchor (Lowe's has one branded "TOGGLER") and get plenty of capacity. Plus, you can use them in any location (excluding wire runs, as noted above) without worrying about hitting a stud after you've bored a giant hole in the drywall.

  • Thanks for the info ... the problem with the self-drilling drywall anchor is that it looks like it still utilizes space behind the drywall (which we don't have). But worth a shot. Aug 31, 2010 at 20:08

I realize this answer is 4 years after the question but concrete-form walls have a tendency to stick around for a good long time, so...

The concrete form system in the house I am building has vertical plastic strips spaced at 8" on center and running within about 1" of the top and bottom of the form. (So if you look and or dig from the top you won't see it immediately.) The face of the styrofoam has vertical lines spaced about 1", and every 8th column formed by these lines has Xs in it to mark where the "studs" are. They hold drywall screws just fine. The Xs are hard to see even in good light, but I found that they have an extra vertical line down the middle of that column as well. Of course different brands will vary in construction and marking, but I'd be surprised if there weren't something similar in yours. Something needs to hold the form together while it's being constructed, and builders and homeowners expect to be able to attach things to walls, so a product that couldn't meet these requirements would probably not last long on the market.

  • I understand what you're saying. But, alas, I don't believe it holds for my house (it's not the first (nor last) oddball feature). I lost a 16' section of siding and have have a clear view of 16' of my exterior styrofoam - with no vertical striping whatsoever. The siding was held on by some sort of glue and 1.5" staples (stuck into styrofoam). Jul 31, 2014 at 17:07

You can always drill into the concrete (behind the foam) and use a 4 or 5" concrete screw (Tapcon). Should be good for 300 lbs per 1/4" screw. Don't hit any wires or pipes burried in the foam


I just finished wiring a home that was built with the ICF. What I did was start at one corner of the home and measured how far from a certain corner each vertical wiring run was, how far from the floor (or ceiling) each horizontal run was depending which one it was closer to. I also indicated the length of each run and beginning and end.

I did the same for the plastic "studs" that are embedded every 8". Beginning at one corner and allowing for drywall thickness, I measured to the first one and every 8" after that you should hit one. Mine were also about three quarters of an inch below the surface, so with half inch drywall it'll be an inch and a quarter deep before you hit the plastic. I'm going to copy it to some other information about the home that the new owners will definitely need just to make things easier(like hanging pictures or whatever). It took a good day but in the long hopefully it will help.


When I build my house I installed a drywall screw 36" from the ground at every plastic firing strip. After dry walling I just use a stud finder to locate the screws.

  • Is this a standard practice that could be used by all, or is this an excellent idea you had and did to your house? If it's just something at your house, then it is, unfortunately, not of much use to others, and really doesn't address the OP's issue (from 10 years ago).
    – FreeMan
    Feb 2, 2021 at 17:39

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