Monthly Archives: April 2015

Ordering the Steel Arches


Posted on April 27, 2015 by

The skeletal steel frame of my earth sheltered house is critical to its success, and getting from the plans to hard steel on site took a lot of effort and is therefore worth a post…

I’ll probably end up putting notes about the more nitty gritty details and lessons learned into the technotes and design tips section of this site…  When I am done learning.

In the meantime,

here is the video.

Steel frame basics

So, the structural design of my house is essentially Shotcrete sprayed over a steel frame skeleton.  You may not see this often, but you can find many examples on line.

Check out some examples on the Formworks site (their facebook page is excellent), or the site of their brother company, PBSI would love to know the falling out story behind that split, but it is clear that the brothers did their early work together because a number of homes are shown on both sites.  After the split, the Formworks designs get pretty interesting, while the PBS designs stay pretty simple in terms of geometry.


IMG_2103Formworks uses 3×4 I-beams to span vaults of up to 50ft across.  They weld Z-brackets on the side of the IBeams to make it easier to add the rebar later.  Special brackets are bolted to the slab foundation and then the I-Beams are slipped into place and bolted to the brackets.  The rebar is dropped into the z-brackets and they are hammered down to lock tight.  They also have a variety of specialty hardware for bolting the IBeams together, attaching floors, etc.  It is a pretty good system, aimed at helping the “do-it yourself” earth sheltered home builder be successful, and refined over many years of actually building these sorts of homes…IMG_2097




So, why would I try to improve on that?

VisitWell, for starters, I didn’t really like the large flat front parapet wall design that many of these homes end up with…  I guess it looks pretty good if the home is mission style, but I was wanting something that looked a little more integrated with the earth.  I wanted the hard edges a bit more broken up.  It is just personal taste, but I wanted something more like a single story “Hobbit home” than a 30 ft tall “Lonely Mountain” edifice.  This meant that I was going to be keeping my heights and spans low.  I also couldn’t resist the idea of mixing and matching in a whole bunch of different arch forms.  The resulting jumble of small arches required a new approach.

My wife and I have talked a few times about how stringing together 4 Quonset huts would have saved a lot of time and money.  I would be done and writing my earth sheltered book by now if we had gone that route.   I actually had some pretty good ideas for how the exterior could be softened (we were going to go “modern wave”), but we couldn’t agree on a good way to finish the interior and we had already put so much thought into the other plan…  But maybe a simpler plan would be a better idea for you?


My overly complicated design includes 3 groin vaults, 3 apses, 10 radial vaults (of 3 basically different sizes), a portion of a “toroidal” vault and one simple vault over the mud room.  In some cases, those steel arches are sitting on precast concrete ribs or spanning shotcrete walls.  It was a lot to plan out.


Square or Round tube?

Originally, I had planned a mixture of both square and round tube (based on tangency to the ceiling below), but I ended up switching to all square tube because it is stronger in its primary load direction (because there is more material where the peak stress occurs) and costs less…  But I later discovered that it is harder to roll-form (without deforming or collapsing).  Paradoxically, some places insisted on the steel being thicker (0.1875 instead of 0.12, or 50% heavier) so it would be easier to roll.  The company I ended up with just took their time and the deformation is barely visible.





Radial Vaults:

ArchRadius_A1_ActualThe radial vaults spanning the curved ribs were the most tricky to plan because I needed to adjust the radii of the steel arches for the location and curvature of the precast concrete ribs they were sitting on.   I ended up deciding to have a level interior and used a simple formula (Rarch=2πrθ/360) for the arch radii at each location, but used the 3D model to calculate the length of the spacers between the arch section and the curved concrete ribs.


Elliptical Arches


Again, in order to avoid the “flat south façade” look that too many earth sheltered homes end up with, I wanted the dirt to spill down around the bedroom windows. I decided to “miter” the corners.  It seemed like I should use properly shaped steel to get that miter shape right and that required ordering “ellipse” shaped frames.  This turned out to be quite a bit more difficult than the regular arches.


They basically made them by creating pieces with simple radii and then welding them together.  Then they tweaked them a bit (more of an art than a science) to get them to match a full sized template that they had asked me to make.  The end result cost about 3 times what I would have paid for a simple arch, so I hope the shape they give the bedrooms is worth it in the end.


To make the template, I used the two foci and a string method (shown in the video).  The coolest thing I did there was make a little car out of Lego that had a place to hold the Sharpie and two pulley wheels to hold the string as it went around.  This made drawing a smooth curve much easier.


2015-03-01_20-13-05When it came to quoting me for the arches, it became clear that most companies were quoting me per “roll”, regardless of the length of the roll or even the size of the steel.  Since I had a number of half arches for forming my apses and the corners of the bedrooms, it was clear that I could save some money by ordering those as full arches and then cutting them in half later.  I made all the drawings this way…  For instance, that ellipse piece will be cut in half as a corner piece before it is installed.   It is also easier to weld the legs on straight if I do it before the pieces are cut in half.

Some of the companies were strictly rolling and wanted me to do everything else myself.  The one that I ended up with including the cutting in the base quote, but would charge me 50% more to weld the pieces together.  Since I would still have other welding to do anyway, and because I kind of like doing it, I decided to do all of it myself (or with friends and family).


For the next few weeks, I will be focused on getting these arches welded together, and the bedroom ones in place.  I am also still working on the precast rib forms and trying to get the quad deck guys to come out…


Excavating the footings (again)


Posted on April 24, 2015 by

The video

This video could have been about a lot of things…  It could be about appropriate ways to get you kids involved in construction…  Or about how I tried to hire for this basic task so I could focus on the trickier parts of constructing my earth sheltered home…

But in the end, the worked needed to get done, so I got my 10 year old to start on it one afternoon after work/school. David is a pretty good worker, but I didn’t mind him taking breaks (lots of breaks) with the bee bee gun.  On another cool spring day, I went out there with my younger son.  Generally speaking, they are very different personalities (Michael is also younger and therefore less suited to digging or working independently), but I was still pretty proud of how well Michael worked.  He also enjoys the bb gun, but he actually spent most of the evening with me working on the rib forms (a separate video). On each of these evenings, we took a break to go walking (and shooting) in the woods.


That Saturday, the whole family came out.  While I was working on welding steel arches (another video entirely), the rest of them got to digging.  My wife, Sherri, did the majority of the excavation until the bedroom footings were completely uncovered.

I took the following Monday afternoon off work and came back out.  This time, I managed to hire some students to excavate while a friend helped me with welding.  These two teens were scratching their heads as they uncovered my footings like archaeologists with no idea of what layout to expect.

Side note here…  I had some trouble with my generator (mentioned in another video) we ended up taking the carburetor apart, etc.  It turned out the carb was fine.  The oil level was just a tiny bit low and the “low oil” sensor was “almost” shutting things down as the oil was drawn up into the engine.

It took the teens several hours to clear the footings.  My wife thought that was money well spent.  Next I had them switch to clearing all the bracing wood out of the basement.  We ended up moving it away with the skid steer.  I offered them a 3rd job, but they were pooped and decided to go home instead.


Now that the wood is out of the basement, we can try to get these teens back to help clear the concrete slag out of there.


Generator Repair


Posted on April 18, 2015 by



Noun: the occurrence and development of events by chance in a happy or beneficial way.

“a fortunate stroke of serendipity”

synonyms: (happy) chance, (happy) accident, flukeluck, good luck, good fortune,fortuityprovidence; happy coincidence”the consequence of serendipity is sometimes a brilliant discovery”


I first discovered the concept of earth sheltering serendipitously while looking for something else on the web.  I don’t even recall what, but it was something unrelated.  I ended up stumbling across Peter Vetsch.  Maybe others will stumble across my site?  Why do I care? I would eventually like to put a book together and traffic to this site may help a publisher agree that there is a market for it…

Anyway, speaking of unrelated tangents…  My generator has been causing slowdowns lately by shutting down for no apparent reasn.  Anyway, last weekend, I got tired of walking back and forth to restart it and decided the problem had to do with the RPM setting being too low.  My generator doesn’t have a nice little screw to adjust the throttle, instead, I needed to loosen and reposition the whole throttle arm.

For one second, I ran the RPM up too high.  I quickly shut it off to avoid damaging the engine, made the adjustments and got the RPM where I wanted it.  The original problem was actually solved simply by topping up the oil because it was just low enough that as the oil went up into the engine it was tripping the low oil sensor to shut things down…  But then I noticed that I wasn’t getting any power out of the plugs…

I didn’t have my multi-tester out at the property with me, so I ended up bringing the whole generator home…  I worked it out and then decided to make a video to show how.  More people search the web for info on fixing generators than looking for earth sheltered homes, maybe this will introduce some serendipity to their lives.

This was the same idea behind posting that timelapse camera comparison video a couple weeks before.


The Video


The Capacitor

CapacitorBrushless alternators use a capacitor to introduce a charge into the windings.  This gets them excited so the alternator will produce electricity.  When my engine RPM surged, it surged the alternator and the capacitor blew to protect all the electronics downstream…

If the alternator is working, it produces a ~5 volt difference (plus or minus a volt or 2) across the capacitor.  So, I just had to check the AC Voltage with my multimeter.  It turned out the voltage was OK.  By process of elimination, I decided to order a new capacitor.

My original was covered with a layer of rust, so I couldn’t read the specifics.  I checked the internet to find the right one for my generator, a 40µF, 370VAC generator capacitor.  The genuine PorterCable part costs 60$.   Now that I knew the specific properties, I was able to search based on that and found a Genteq knockoff that only cost 16$ with delivery.   It claimed to be just as long lasting (60,000 hours), and like the much more expensive OEM product, it is also “self-extinguishing” so I won’t die in a terrifying fireball if it fails.

Its physical dimensions are a little different, but it fit.  And more importantly, my generator works again.

Now my generator can do its job and give me electricity on my jobsite.