This weeks focus was on preparing for Shotcrete… The basic studs and lath were up, but we needed to get all the rough electrical and rebar in place. Sherri and I had a lot of work to do.
Here is the video.
The electrical rough-in inspection must be done before the walls are closed up. Usually, that means before drywall, but for us, it means before shotcrete. In our township, electrical inspections are done only during a few specific hours each week, so we had to catch the two-hour Wednesday morning slot or Shotcrete would be delayed to the following week.
I has carefully designed the electrical layout weeks before, and then tweaked it based on Sherri’s input. Now, Sherri and I just needed to work as quickly as we could to place the boxes, run the conduit and then finally, pull the wires thru. We used Carlon ENT (smurf tube) and I had quite a hassle getting all the boxes that I needed. Next time, I will order in advance, but that is another story.
The process took longer than I expected, you can see I am working on it several days the week before. We still had work to do on this inspection day, so we came in very early and got going. We had not been finished long when the inspector arrived. He was very pleasant and actually said he appreciated that we were doing the electrical ourselves. That was a surprise because I expected that any inspector, especially one who was a professional electrician himself, would be somewhat against the idea of home owners taking on their own electrical. He made a few small suggestions for how to keep concrete out of the openings, and handed us our “approved” inspection paperwork.
Next, Sherri and I got going on Rebar. Mostly, I was cutting and Sherri was tying.
At the end of the day, my friend, Nate, arrived to check out the site. He had been up from Indiana for a conference in Ann Arbor. He reminded me that I had first told him about this idea at my dining room table nearly 6 years ago. I didn’t ask if he thought I was crazy, then or now ;^)
This week included an overnight work party at the property with some friends, Aaron and Ryan. We headed out after work on Wednesday and got in a few hours working on the window well until it got a bit dark. Then we had a nice camp fire (using my rocket stove) and talked until past two in the morning.
The next day, we got up before 7 and worked on Rebar until they had to go mid-morning. At 9:00 AM, my N-12 pipe arrived and I was glad to have my friends there to help me unload it.
After they left, I tied rebar for a while, then spent a few hours on off camera tasks like getting new tires and parts for my skid steer. Eventually, I got back and spent the rest of the day on Electrical.
Here is the video.
Extra Info;
XPS forms?
I wanted to use a different approach for forming the window well… Partially because I wanted to experiment with different methods and partially because the window well is more exposed to the environment and I didn’t think the metal lath and studs would be a good idea. I originally thought I would just do it with plywood sheathing and 2x4s.
On the way out to the property, we stopped to pick up a trailer full of wood at Home Depot. Sheathing Plywood is actually pretty expensive. More expensive than tongue and groove 1” rigid XPS insulation… So we switched plans on the fly and bought the XPS instead. I also considered going with OSB, Oriented Strand Board), and bought a couple sheets, but didn’t use them. The XPS was easy to work with and I am pretty happy with the decision. The test will be when we shoot the shotcrete at it. XPS is tougher than the EPS backing that I saw used with shotcrete last year, plus it is firmly attached to treated 2x4s, so I think it will be fine.
At the end of the day, I think the XPS and 2×4 approach was easier to assemble. However, it is also more expensive, especially if you are building forms more than 8ft tall.
Curving rebar?
For curving the rebar, we tried a few things, including the rebar hickey. The main difficulty is getting the right curvature and all in one single plane. Bending rebar is easy, curving rebar to a precise shape takes technique. The winning solution is shown in the video.
We stand on the rebar and pull one side up a certain amount (experience helps). Basically, it is not really a continuous curve, but more piecewise linear. When the raised end becomes two difficult for one person to manage, one person holds it vertical (in plane) so the other person can do a similar bend from the other end. Due to the way that steel stays in the elastic range for a while and then yields for a permanent bend, we need to over bend it to start. So the second step is to push it down flat, again keeping it in plane. (an improvement I worked out on a later day was to walk it flat instead of using our hands to wrestle it down). When we let it go, it springs back to a curve with a larger radius.
We had marked the radius we wanted in the sand and we set the curved rebar in the sand “template” to check it. Some of them were right on. If they needed any adjustment, one of us would stand at the point where things started to go off the line and the other one would pull the rebar horizontally and adjust it into shape… The adjustment is actually so fast and easy that the timelapse camera, with a 10 second period, didn’t catch us doing it.
Electrical
The electrical takes longer than I thought I would… I have a plan that I am referring to, but actually wresling the blue Smurf tube (ENT conduit) into position thru all the right holes is a bit tricky.
Also, my plan didn’t take into account how many tubes would leave each box and their directions.
NEC code prohibits bending the ENT by more than 180 degrees along its length. Each box is attached to a stud. In many cases, the stud blocks one side of the box and leaves only 3 knock outs for the conduit to attach to. These are in a chain, so a light switch needs one pipe to carry electricity in and other to continue the circuit to the next switch. A third tube goes vertical toward the ceiling where we will eventually put the light fixture. Ideally, the third tube would come from the knock out at the top of the box. The problem happens when the power is coming from above (such as over a door). If I run it down and around to the bottom of the box, it would exceed the 180 degrees of bending that code permits. Instead, I must run it into the side of the box and run the “out” tube from the bottom of the box even though it actually needs to go sideways… What if I also want to branch my circuit in a second direction? Anyway, it takes some head scratching. I will shot for an electrical inspection next Wednesday.
Sourcing
When you walk into Home Depot, there are lots of big signs about ordering online. This is because they don’t have everything in the store. For instance, none of the rebar tools on the Home Depot website are actually available on the shelf. However, it also helps for buying cases or quantities not available in the store. If you buy individual outlet boxes, they cost about 2 dollars each. If you buy them in bulk, you can get a case of 50 for $38, that is about half the price. But you can only buy the case on line. Also, for some reason, the stores only stock 100 ft lengths of ¾” ENT tube. The ½” tube costs quite a bit less, but only comes in 25ft lengths, and if you buy 4 of those, it costs more than the ¾” ENT tube in the 100ft roll. The only way to get ½” tube at a good price is to buy a 200 ft roll on-line (which costs just a little more than the 100ft roll of ¾” tube). Get it? Good.
Problem is that it doesn’t always work out right. I ordered a case of 50 outlets. It was 1 case, so the quantity was listed as “1” and the amount charged was ~$38.00. I chose to pick it up in the store. When I went to the service desk to pick it up, they had set aside one single box for me… I showed the girl my smartphone with the email showing I had been billed for a case, but there wasn’t much she could do except put it back as if I had not come in to pick it up. They didn’t have any in stock at that store. I ended up driving to two other stores in different cities trying to find enough boxes to finish my job.
I got an email today saying that if I don’t pick it up soon, the order will be canceled, so I guess I don’t need to do anything.
Most of the electrical system for an earth sheltered home is pretty conventional, but there are a few differences.
Ground
Good electrical ground is able to dump many amps of electricity into the earth with as little resistance as possible. It is important for occupant safety, and surge protection (including lightning).
Code can be met a few different ways, but most electricians use one (or more) 8 ft grounding rods buried in the earth. Since it is all about conducting electricity into the earth, it all works better if there is moisture in the earth. Most electricians will try to bury one or two rods (separated by at least 6 ft) somewhere near a corner of the house where a downspout is likely to dump water.
If you are putting in an insulating umbrella that will keep the earth under your home dry, you will need to move your grounding rods out much further away from the home than an electrician normally would.
Since many earth sheltered homes have concrete footings full of rebar, it may seem logical to use a “concrete encased electrode” in the foundation (aka Ufer ground). Normally, a concrete encased electrode is a very effective grounding system and the NEC allows it to be used as your only grounding. However, this method is not as compatible with the earth sheltered umbrella and other water proofing measures that will keep the soil around your foundation very dry. Again, dry soil will not conduct electricity as effectively.
There have been cases when lightning strikes actually cause the moisture in the concrete to rapidly expand, crack and occasionally explode
Another popular option is attaching the grounding system to a galvanized well casing (an uber grounding rod). This can work well and should certainly be done if you have a metal well casing. PVC casings cost about 1/3rd of a galvanized casing and never corrode. Obviously it is not worth paying three times the price just so you can use your well as a grounding rod, but some areas still require the metal casings for all or at least the first 20 ft of the well. Find out the rule and costs for your area and plan accordingly.
Grounding is very important to the electrical system of a home and is probably one of the areas where you want to exceed code. I will probably start with the “concrete encased electrode” and also put in a few extra grounding rods and tie onto my well casing (if it ends up with a galvanized casing).
Conduit
With my construction method (steel covered in shotcrete), I don’t have wood frame walls (or even wood furring strips) that I can run wiring through in a traditional manner. This is probably the reason that electrical contractors all gave me such ridiculously high bids. My walls start with a framework of steel studs and rebar. I will need to run my electrical conduit in through that. There are several types of conduit that the NEC (National Electric Code) will accept for concrete encasement. Some are more expensive or difficult to use than others.
The above chart only tells part of the story. The first two rows, PVC Conduit and Electrical Metal Tube, come in straight 10 ft pieces. They can be bent, but that is much more work than the flexible tubes. There are also a lot more fittings when you have to put at least one every 10 ft, and the cost of fittings really starts to add up. EMT and PVC also take a lot more work to make each connection.
The Liquid Tight Flexible Non- Metallic tubing is really designed for situations, usually industrial or agricultural, where the conduit frequently gets liquid on it. This is really overkil for a residential wiring application. It does come in long flexible lengths, but its fittings are expensive and a take much longer to apply than ENT. The real killer is the price, although I did see some very reasonably priced at the reuse place.
That leaves us with the Smurf tube as the cheapest and easiest overall solution for most of the conduit.
My recommendation is to use a combination of PVC and ENT. The PVC is the cheapest per foot, comes in a wide range of sizes and can be buried directly. You can also use it in straight walls or even bend it a little with some heat. The ENT, with its long flexible coils, is great for longer runs through curved walls.
And the Electrical Metal Tube will look great in my steel Quonset hut garage.
ENT, Smurf Tube
The NEC stubbornly refuses to call it Smurf tube and instead insists on calling it ENT (Electrical Non-metallic Tubing). They cover it in article 362 of the NEC. Here are some of the highlights;
ENT is allowed to be encased in concrete, but it is not considered strong enough to be buried or used in places where the ambient temperature is greater than 122°f (50°c). Because of the temperature limits, it is not allowed to carry more than 600 volts. There are other weird rules about not allowing it to be exposed if the residence is more than 3 floors tall. Also, even though it is flexible, you still need to pay attention to the conduit rules about the number of turns (the degrees can not exceed 360°.
The flexible connections just snap together (no need for glue or any other tools), but I think I would tape the joints before adding the shotcrete.
Boxes
Your choice of Boxes is related to your choice of conduit. If you are encasing them in concrete, you should probably go with plastic (rather than metal which has gaps and can rust).
You want the kind that connects the conduit right into the box (round holes) rather than the kind where you just push the wires through little square trap doors. If there are any little gaps, tape them to keep the concrete out.
The boxes generally assume that you are attaching them to wood. Some come with nails built right in. You will need to figure out a way to properly attach the boxes to the rebar. When I figure it out, I will come back with pics. It needs to be tightly fixed to make the inspector happy, but you will also want it to stay where you put it when the heavy shotcrete is slamming into it.
Books
If you need to save a bit of money by doing the electrical yourself, or if you just want to keep a better eye on what your electrician is doing, you may want to do some reading.
I summarized my favorite Electrical Books here…
