The day after shotcrete on the perimeter walls, we got started on prepping the steel arches and setting them up for another round of shotcrete. This particular apse is special because it will eventually be my office (where I will spend most of my waking hours), and because it needs to be in (along with its retaining wall) before we can bury the garage side of the house. The work was all pretty simple compared to the bedrooms, and I didn’t take much time to stop and take pics, so this post should be short. But first, the video…
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An apse is the semi-circular end of a vault. They are pretty common in earth sheltered homes because they can hold a lot of load, but usually, they are at the back, completely buried. I put mine up front and included a window. Hopefully, it turns out to be a good idea. This apse will also be my office, and I spend a lot of the time on video conference calls, so hopefully, the acoustics are OK. At least my head will be near the window and not near the acoustic focus point.
This is how the guest room looked the morning after shotcrete.
It looks warm enough in the pics, but the temp was probably less than 40 and freezing over night. I left this propane heater in the room to keep the roof warm while it cured.
I was pretty happy with how the mud room roof turned out…
This is the top of the playroom apse. Because it was out in the open, it also needed its own little parapet wall…
Hunter checking on the camera as he flipped the steel arch. He had welded 3 sides of each leg, but needed to flip it to weld the 4th.
Positioned the first arch here and took a quick pic just to get an idea of the scale of the office…
The office apse steel at the end of the first saturday…
Here I am looking quite grizzly, but happy things are working out.
Office apse with mostly just the horizontal rebar.
Michael messing with the camera… He likes moving past it very slowly so it looks like he is moving normal speed and the rest of us are high speed.
Snow stopped our progress for a couple months.
Sherri did most of the lath work during a brief warm spell in February… Sorry, no timelapse.
After welding the legs on the steel arches, it was time to assemble the bedroom structure. The basic elements are the steel arches, placed on the bases and connected by rebar. The bases were just 3/8th inch thick steel plates with #4 rebar pegs to hold the plates in place. The pegs were welded to the plates and the arches were welded to the plates. Small pieces of rebar were welded to connect perpendicular arches to stiffen the assembly. Horizontal rebar was tied on first, just to get things in place, and then that rebar was welded to the structure so it would be safer to climb on. For the vertical rebar, we started with 5/8ths inch holes drilled right into the footing. I curved each piece of rebar by hand and dropped the straight end in the hole. We then tied (and eventually welded) each vertical piece to the rest of the assembly.
Some of the little side stories are best told with captions, so here is a gallery
You may recall that we had steel arches rolled (curved with big rolling wheels) into arches. However, these arches needed legs welded to them. They also needed a way to fasten them to the footing and a way for them to hold rebar.
The first two of those ideas are looked at in this video. Details and how we attached the rebar are included in this post…
Welding the arches
The steel fabricators that rolled my arches are also expert welders (among other things). I did get a quote to weld the arches together, but it was $6000, and that was just for the 30 arches on the bedroom side (not the other arches in the radial vaults). That is about 100$ per leg welded on, or, assuming 4 welds per leg, 25$ per weld… And that doesn’t even weld the arches to the feet or attach any rebar. I assumed the quote meant that they wanted me to learn to weld, so I bought a cheapwelder on Craigs list (a couple hundred bucks got me fully setup) and practiced so I could do it myself.
The arches arrived on site in early may. All the half circles had been cut to 180 degrees. Some of the larger ones were actually segmented in 2 or 3 pieces so they could more easily be delivered. The Elliptical arches were not trimmed (I would need to use my template).
My sister came out to help and we spent the morning practicing and getting the settings right on the welder. When it came time to weld the real arches, we first needed to assemble the pieces together and we needed the legs to be parallel. We did this by setting things up with equal diagonals and then building a brace jig, like a truss, to keep things aligned correctly. The jig took a few extra minutes to build, but we had a number of arches of each size, so we were able to re-use it and save a lot of time later.
Early in the welding, we were very serious and wore all the gear and clamped the jig on again after flipping the arch to weld the bottom… By the end, I stopped wearing the jacket, switched back to sandals and didn’t worry about the jig after the initial welds were in. Actually, not wearing all the protection helped train me to be a better welder. There is nothing like hot metal burns to teach you how to weld without sputtering.
I did, however, keep wearing the gloves. I found the best way to weld was to old the gun with both hands and to rest one of them on the work to stead the gun. The other hand could then control the gun with good fine motion control.
I also learned the importance of keeping that shielding gas concentrated around the work and how sensitive the welds were to the settings on the welder. If the wire speed was too fast or two slow, welding became difficult, and experience taught me to quickly realize that I needed to adjust the settings up or down for the conditions.
Along the way, a number of people stopped by to try their hands and welding. Only one of them had any prior experience (and he taught me a thing or two).
My 10 year old also got a few good welds in.
Of course, I ended up doing most of the welding by myself. I could weld and move the small arches; but larger arches were very awkward (and just a little bit heavy), so I relied on my wife, Sherri, to help move them. At one point, Sherri tripped (on a piece of rebar) and lowered the arch as she caught her self, but the welds were still hot, so she got a nice burn on her shoulder. We gave the steel lots of time to cool after that. I started staging things so that instead of welding all the arches of the same size in a series (where I would need to move arches between each set of welds), I would weld a set of “nesting” arches (of various sizes) that I could weld all at once and leave on the ground until Sherri could come out to help me flip them all.
Steel arch bases
As I have said before, my best example for this sort of construction is “Formworks.” Check out their Facebook page for lots of great pictures. These guys have lots of experience and they know how to make the process doable for the do-it-yourself market. They have features like brackets that you bolt to the ground and then the steel arches fit into them and are bolted in place. They also have Z clips pre-welded to the sides of the arches so you can easily place rebar and just hammer the clip to lock it in. The catch is that all this convenience comes at a steep price. I needed to come up with a much more cost effective way to get the job done.
I considered buying scaffold feet (as I had for the tower columns), but they were about 5$ each and would need to be bolted down with 4 bolts in 4 drilled holes. That would mean careful alignment and lots of time drilling.
If I stripped the requirements down, I needed 2 things. 1) a bearing surface to spread the weight of the steel out so it wouldn’t penetrate the footing. 2) a vertical pin to keep the leg of the arch from moving laterally. There was no need to prevent rotation, so i really only needed one hole, and there was no need to prevent lift, so I didn’t actually even need to bolt the feet down.
My final solution was just a 4×4 inch steel plate, 3/16ths of an inch thick, with a hole in it. I would use a piece of scrap rebar as a pin to keep the plate and the steel arch in place. I got quotes on getting these made and was told hundreds of dollars. I forget the exact ridiculous number, but it worked out to nearly $8 dollars per drilled hole. So I decided I would take care of this myself. The savings would pay off my drill press for the second time.
To position and assemble these bases, I drilled a single 4 inch deep hole in the footing and put an 8 inch long piece of scrap rebar thru the hole in the plate and into the hole in the footing. I then welded the rebar to the steel plate with 3 tack welds. I didn’t grout or epoxy or bolt anything. To set the arch, I would simply put the end of the steel tube over the rebar, adjust the location a bit and then weld it to the metal plate.
This solution was cheap to make, and quick and easy to install. The only catch was that I needed to weld each connection… This is a pic of a place where three of these bases were near eachother, so I used a “double” plate and welded it to the adjacent “single”.
Attaching the horizontal rebar
Placing vertical rebar is easy, you just drill a hole in the ground. Attaching horizontal rebar to smooth steel tubes is harder. If you tie it, it may just slide down. Welding everything in place as you go would probably be too time consuming and would require more hands than I usually have.
I decided to try and find a cheaper way to replicate the basic idea of the Formworks Z brackets. I started by looking at prices of various channel steel that would work. As usual, buying actual raw materials is not the cheapest way. I found that I could get steel shelving pieces (made in China) for the best price. I would just cut them into 3/4 inch slices and weld them to the frames myself.
I prepared about 5 of these, but when I added up the cost of materials and my time (at only 10$ an hour) for slicing and grinding down the excessively sharp edges, they came to about $0.50 each. And that didn’t even include the time to weld them to the frames and I would have hundreds of these.
Another idea was to weld S hooks to the sides of the frames so that one side of the hook could catch the rebar. I bought a few of these for about $0.25 each, but couldn’t find a good bulk price. I found that they were easy to weld in place, but the opening was a bit tight and I would need to hammer them open a bit to better receive the rebar.
Then I decided I could just buy a big box of nails ($0.01 each) and weld those on at an angle to catch the rebar. Then I could just hammer those over to hold the rebar firmly in place. But the welding task was still daunting and my wife thought they created a real hazard on the job site. “You’ll poke your eye out kid.”
Then I decided to break it down to its simplest concept. I couldn’t just wire the rebar to the smooth vertical steel tubes because it would just slide down. All I needed to do was stop the sliding. I decided to notch the steel with my grinder. I made the notches every foot (my horizontal rebar spacing) and made sure that the tie wire caught the notch… Problem solved. The cost was very small (one $2 disk could make all the notches for the project) and no welding was required. Actually, my friend Aaron brought me a 10 pack of metal cutoff disks that he had for some reason, so it was all free to me.
Mistakes were made
Perhaps in my misguided effort to be a good host, I made a few mistakes by setting up a few early arches without first carefully laying out the locations of all the arches. This meant that my first few arches were welded in place before I noticed that I had some how made a 5 degree error in placing the first one… I ended up “adjusting” the other base locations to try and sort out the locations, and it will all work out, but without the crisp straight lines that I originally thought I wanted.
German vs Spanish
Online, you can find many examples of “German” earth shelters where the construction is very precisely planed out and executed. Even if they have “free form” shapes, they are constructed very precisely to the specified forms. You can also find many “Spanish” examples (including many in Germany ;^) where the builders basically hand formed the rebar arches as they went, perhaps based on some rough sketches, and ended up with a much more organic free-form design.
I had started this build with a more “German” ideal in mind. I used Marino Ware studs to get perfectly vertical walls. I had the steel arches rolled by professionals to exacting specifications. The design its self was very euclidean geometric so that I could precisely work out all the angles.
But as it is going up, small mistakes (mine and others) and approximations are adding up and it is becoming more and more “Spanish”. My epiphany was when I realized that this was because I was the one making many of the approximations, and that, perhaps, I was a bit “Spanish” in my construction. I also decided that it will still all work out, even if it ends up looking a bit more organic rather than purely geometric.
In the next post, we will finish erecting the steel arches and start putting up rebar. I just couldn’t fit it all in to one video/post