Electrical in ICF Walls

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When we decided to build with ICF blocks, the first question we had - and many of you had - was how the heck to do run electrical in the walls?  

For those of you new to the Momplex blog, the Momplex is actually built out of foam blocks.  We used ARXX blocks, and the technical term is ICF short for Insulating Concrete Forms.

Was she really that little then?

The blocks are lightweight and hollow in the center.

You simply stack the blocks just like legos, one on top of the other, interlocking.  Inside the blocks, you place rebar for reinforcement, and then pour concrete.

The concrete fills the void and creates the structure of the building, and acts as a vapor barrier.  The foam stays on as the insulation.  And the black webbing is designed to be used as a fastening strip for attaching siding and drywall.  It really is a slick system and you end up with a super insulated wall.  

But how to do electrical?

I've heard the term "hot knife" but haven't quite warmed up to the idea yet.  Exactly how is this all going to work?  

Let's find out!

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Step 1 Diagram: 
Step 1: 

This is the hot knife. basically, the blade out front heats up and melts the foam, cutting it.

Step 2 Diagram: 
Step 2 Instructions: 

For an electrical box, you set the depth of the wire blade to the depth for the electrical box. Remember, we still have drywall to add, so the depth is set in 1/2" to accommodate drywall.

Step 3 Diagram: 
Step 3 Instructions: 

Then we mark the location of the box on the ICF.

Step 4 Diagram: 
Step 4 Instructions: 

And start by inserting the hot knife in at the bottom. Notice the hot knife blade for electrical boxes is sized just right in width, so all you have to do is get the height of the box right.

Step 5 Diagram: 
Step 5 Instructions: 
The hot knife goes in smoothly and easily. You don't want to force it, but you don't want to melt the whole wall!
Step 6 Diagram: 
Step 6 Instructions: 
Once the knife is all the way inserted, you can let the hot knife rest flatly on the foam, and just move upward or downward.
Step 7 Diagram: 
Step 7 Instructions: 
Here we move upward.
Step 8 Diagram: 
Step 8 Instructions: 
All the way to the top of our box outline.
Step 9 Diagram: 
Step 9 Instructions: 
When you reach the desired height of the electrical box, just pull the hot knife straight out.
Step 10 Diagram: 
Step 10 Instructions: 
And remove the foam cut out.
Step 11 Diagram: 
Step 11: 
And insert the electrical box! The electrical box is attached to the concrete poured in the center of the blocks with concrete anchor screws to keep in place. After wiring, around the box can be spray foamed as well to protect from heat loss. So that was easy, but I know a lot of you smart folks are also asking how do you get the wire to the boxes? There's nothing that get's by you!
Step 12 Diagram: 
Step 12: 
Well, you use a channel blade for the hot knife. Just set to desired depth.
Step 13 Diagram: 
Step 13: 
And insert and move along!
Step 14 Diagram: 
Step 14: 
And just go with it!
Step 15 Diagram: 
Step 15: 

Then you can pull the cut out out and run your wire.

We are demonstrating on a scrap piece ICF, so you may notice we ran into a black fastening strip.  What you do in practice is run the channel at the joint between two blocks, where there is no fastening strip.

So we will be running a channel all the way around, one block up, to run wire to each electrical box.

One thing we can't stand about our current house is not enough outlets, despite building to electrical code.  Its always a hunt to plug a laptop in!  So we will be putting extra boxes in just to make Mom's life as easy as possible.  We've definitely got our work cut out for us today!

Have you done ICFs?  What did you think of the electrical process?