Wiring Our ICF Off-Grid Home

The first thing I have to say is please don’t attempt to do any wiring of any kind unless you understand electricity and the proper way to install electrical boxes and circuits.

Mounted Outlet and Wire Grooves

I don’t want to hear about any shiny red fire engines with lights flashing and siren blaring that needed to be called when the 12 VDC gizmo was wired to 120VAC and showed its’ displeasure by going full flame on. I’m not going to get into how to wire the house. But I will pass on some helpful tips on wiring our ICF off-grid home.

Electrical Runs in ICF Foam

One of the obvious problems with an ICF foam insulated house is there are no wall cavities to run plumbing or wiring. Rather, there is solid concrete between the 2 foam forms. So each wire will need to be buried within the foam itself. I’ve read a number of different ways to work ICF to not only run wiring but install electrical outlets and switches.

One method is to purchase an expensive heated wire device that cuts through the foam like butter. A very nice tool. But when I priced it, I believe it was plus or minus $600. I’d rather gnaw channels in the ICF with my teeth than pay that price for a one time use.

After a bit of thought on the subject, I came up with the idea of using a diamond metal cutting blade on my circular saw. I originally bought that blade to cut all the reinforcing rebar for the ICF forms. And it’s the tool I’ve used to cut the exterior metal to size. I had no idea what would happen when I tried to cut ICF foam.

Diamond Blade

I tried the concept on a scrap piece of foam we had laying around. As it turns out, the blade is just about the perfect width for a wire channel. And because it does not have an aggressive toothy blade profile, I’m not churning out a pile of foam bits. As I cut my channel, it seems to burn a smooth channel with a bit of very fine powder.

I set the blade depth to about 1 ⅝ inches, which buries the wire in the foam 1 ¼ inches, the minimum depth according to the Nudura manual. I slightly wiggle the saw from side to side as I cut just to expand the width of the channel a tiny bit.

The circular saw is good for cutting the majority of a run but because of the saw’s size, there are sections it can’t cut, such as close to the floor. In other words, if I have a wire coming up from the basement, my circular saw can only start about 5 inches above the floor. In that event, I simply use a key hole saw to finish the groove. The great thing about the ICF is that it has all the scored lines in the surface. So it makes it easy to make straight grooves with the circular saw by using a handy line as a guide.

Once my channel is cut and finished if need be with the key hole saw, it’s time to slide the wire in edge wise. I use a blunted piece of shim stock to push the wire in and properly seat it in the bed of the channel. It’s a tight fit so it will stay in place if done correctly.

Electrical Box Mounting

Mounting electrical boxes in ICF walls was another challenge I had to overcome. There are special plastic boxes made for the purpose but I chose to use a metal box with a mounting flange. I had to modify the boxes which was quite easy to do. There are 2 mounting flanges on each box. The obvious one that is in the way needed to be removed. The easiest way is to use a hand grinder and cut it off. There is also a metal protrusion fastened with rivets that I ground off.

Modified Versus Unmodified Electrical Box

I made all our outlet boxes 18 inches from the floor. You should check to see if there is some electrical code specifying a height. I am not aware of a code for height other than a typical standard that electricians use. Eighteen inches is a good height for us relative to where the ICF seams are on the wall. I want to avoid the seam since there is no plastic web to which I can attach my electrical box.

Outlet 18 Inches From Floor

To locate the electrical outlet, I use an 18 inch stick to make a mark on the wall the correct height off the floor and then I use a wood template the size of my electrical box which I set against the wall in the proper location for marking. I use a black magic marker to mark the box location. One side of my box must be set right up against a plastic web which is embedded every 8 inches in the foam. That plastic web is what I will screw the electrical box’s metal flange to for mounting.

Once marked, I use a small, very sharp knife to cut the perimeter of the box. I make a mark on the knife blade for a depth of 1 ⅝ inch, the maximum depth I want to cut out. That mark gives me a reference point so that when I plunge the knife in to cut, I don’t go any deeper than intended. I cut all 4 sides to the proper depth and then with the same knife, I cut small wedges out to remove the easy material.

At this point, I had another dilemma to overcome. How do I remove the remaining foam to make a nice clean, rectangular hole to park an electrical box? Then I remembered I have a nice set of forstner bits. https://www.popularwoodworking.com/projects/tool-talk-forstner-bits  I use forstner bits in wood working and they were the perfect solution. I popped a 1 inch bit in my portable drill and easily carved the remainder of the foam out to the proper depth in no time.

Roughing Out With Knife-Finish With Forstner Bit

I set the box in the hole and tweak if necessary. If it all looks good, I’ll run my wire into the box, set the wire in the groove and the box in it’s hole and screw the box flange to the plastic web with a couple of screws.

And there you have it. An electrical box ready for an outlet in an ICF wall. The same method of installation applies to a switch box mounted higher up on the wall.

Triple Gang Electrical Switch Box

A word of caution. If you wire the switch, turn it on and water comes out the faucet or you turn on a faucet and a light comes on, best to get some professional help!

Until next time, keep the dream alive! We wish you a great day!

Ron and Johanna

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