Monthly Archives: January 2016

ICF Walls


Posted on January 21, 2016 by


2015-09-02_Aaron&Simon (Medium)

ICF blocks seemed like the perfect solution for the front of my garage where they would be needed as walls for the garage and as a parapet to hold back earth over the roof, without needing any special handling for insulation. There have already been previous posts about my Fox Blocks training and my early work with these.  Now that I am all done with installing my ICF blocks, this post includes FAQs about my lessons learned, costs, etc., but first, the video


Earlier Post

There was an earlier post about why I chose Fox Blocks, the training, etc.  The rest of this post will be about lessons learned since then.


Why pour in a series of small pours?

2015-07-25_Working on 2nd half of Mudroom wall

The more concrete you pour at a time, the more pressure is exerted on the forms and the more concrete will come spilling out if anything goes wrong.  In other words, I wanted to take baby steps.

I also couldn’t pour the front wall at the same time as the back wall because I needed to leave the front open while I continued to make those big concrete ribs in the garage.

I couldn’t wait on the back wall because I needed to mount the electrical service somewhere and the pump truck was cheaper than it would be to start on a temporary structure and then move the meter.

Even brave people are limited by the physics (hydrodynamics) of pouring concrete, so I did pour the front wall in only 2 stages instead of 3.  But even with my growing experience and confidence, I didn’t sleep well the night before we did that pour over the garage door openings.

Why Scaffold Jacks on the north side, but regular scaffolding on the south side?  Why not ladders?

2016-01-16_NorthWallScaffolding (Medium)

When you are building the ICF walls, I guess you could use ladders.  It would be a hassle to keep moving them around, but it would be possible.  However, when it comes time to pour the wall, you need to be able to move swiftly along the top of the wall.  You can not keep stopping the pump truck to climb down and move the ladder .  You need some sort of working platform.

The north wall was poured in stages over a long period of time because I was waiting for times when I had the concrete pump truck coming for other reasons (such as the basement floor or the quad deck floor).  During that time, I knew I would want my scaffolds for other tasks, such as setting up the steel framework.  Home made scaffold jacks were the easy and affordable solution because I could just leave them in place and move them up as needed.

By the time I got to the north wall, I was just paying for the pump truck and doing my pours much closer together, and I wasn’t using the scaffolding for other tasks.  I also didn’t think the jacks would have worked well across the open garage doors anyway, and the driveway was nice and flat for stand alone scaffolding…  So I just used my regular scaffolding.


How much did it cost?

I bought the Fox blocks at Menards, so you can check their website for the prices, but they were just under 20$ per block (16 x 48 x 12 inches).  The walls then got filled with concrete that cost about $100 per cubic yard (27 cubic feet).  There were also some clips and a bunch of wood (I used a lot of scrap from earlier projects), rebar that I already had laying around, etc.   I buy the rebar by the ton, and pay something like 35 cents per ft.  If I do some fun math, and divide things out per square ft…

Fox Blocks = 3.75/sqft

Concrete (6 inches thick) = $1.85/sqft

Rebar = 0.35 cents.


Total = $5.95/sqft,

Plus a few cents for clips, etc.  That is not too bad for a 12 inch thick wall, but it is about double what it would cost to frame a 2×4 wall with 4 inches of insulation and house wrap.  I didn’t have separate steps to attach vapor barrier, insulation, etc. because those are all built in, but clearly, I still spent a lot of time putting up patches, etc.

I don’t regret going with the ICFs because I think they are much better in this application as parapet (retaining wall) for the dirt on my roof. The concrete wall will be much stronger and much longer lasting without any risk of rot, etc. There is also the dynamic R value of the concrete in the wall that will keep my garage much more thermally comfortable.  My wife likes that no insects or mice will get thru it, but in the mean time, some birds are trying to make nests in the exposed polystyrene.

What I left out of the above calculation, because it is a real kicker for me, is renting the pump truck each time. Filling a 14.5 ft tall wall without a pump truck isn’t really a practical option. For the first two sections, we scheduled the wall pours to align with the basement and quad deck floors, so no additional cost there.  However, for the other two times, we just had to pay for them to come out for just a tiny section of wall…  Each pump truck visit was about 700$, which is more than the cost of the concrete we pumped.  Each pump truck also required me to order a couple extra cubic yards of concrete just to fill the hose (that all gets dumped out at the end). If we were doing a larger chunk of the house in one go (such as a whole house built of ICF blocks), we could have improved that ratio a lot.

How about time?

Yes, I did this work over about 6 months.  Mostly that was to align pour days with other tasks that would need the pump truck.  I was also working full time and basically only building on Saturdays and some weekday evenings.  The actual time spent stacking blocks was not too bad.  How would it compare with stick frame?  Probably similar.  Certainly it will last longer.

What was with all those edge patches?


There are no attachment points on the ends of the fox blocks.  They attach to each other, end to end, with clips between the plastic webs.  The styrofoam just buts up against the other blocks, so it has some compressive strength, but no tensile strength for holding screws.  When you attach the end bucks, etc. you need to connect to the high density polyethylene furring strips built into the front and backs of the blocks.  To do this, I screwed boards (like 2×6 boards or sheets of particle board with 2×4 blocks) to the front and back of the ICF blocks and then I could screw the end boards to the sides of these.

I am pretty sure all the vertical end walls and especially the ones for the top of the garage door opening were critical for containing the concrete.  The patches, such as the one along the vertical seam shown in the video, were also critical.

On the top edge of the wall, I had cut a sloping shape.  When we poured in the concrete, if it was too wet (high slump), it may have simply poured out the sides again.  I knew there would be some pressure on these sides, even if it was not as great as the vertical sides, and I wanted to contain and shape that concrete.  The concrete did push at the top/side forms for the first 3 pours, but for the last pour, the slump was so low that the concrete probably would have just sat there in the shape of that hill and let me trowel it smooth.  In that last case, the boards were just in the way and made it difficult to get the concrete down inside where it needed to be.


1) The best tool to cut the ICG blocks with was a battery powered jig saw with the longest blade you could buy.

2) Get a concrete vibrator.  Harbor Freight has a cheap one.  It makes a huge difference to the flow of the concrete, which means you can get lower slump concrete (which sets up stronger) and still have it nicely flow around all the rebar and ICF webs without any voids.

Before buying the vibrator, I had wondered if it would be worth the money.  Professional grade vibrators cost hundreds more.  As it was, I thought it was a great little investment that got me thru all my ribs and my walls and died 5 minutes before the end.  I haven’t needed it since, so I haven’t tried to fix it yet.  Maybe just a switch died?

3) Because the ICF blocks look like lego, any many of us “do it yourself” builders were lego maniacs, we some times assume that overlapping the blocks (running bond) is important.  When something in the wall makes this difficult, we might want to waste lots of time or chop up expensive blocks trying to prevent a vertical seam. But it is totally unnecessary.  Unlike bricks (masonry or lego), the little styrofoam nubs on the ICF blocks do not actually hold the wall together in the long run.  The void gets filed with a monolithic concrete pour that ignores all those stacking details.  Instead, just focus on making sure the surface of the wall is patched so the forms won’t split open along the vertical seam.



Just some related pics.