Tag Archives: Virtual Build

Steel Spine for the Earth Sheltered Home


Posted on March 28, 2015 by

Big Picture

Tower_MichaelArcherAt the moment, the construction schedule has 3 main paths.

1) On the east side, we are getting the steel arches rolled.  We can start to erect those after the excavator comes in and sorts out the grading issue, but they are waiting on the frost laws to allow them to carry their heavy equipment on the roads.

2) On the west side, I am getting the Quonset hut ready as a work shop to build the wooden forms for the precast concrete ribs.

I probably have a months worth of work on each of these sides before the paths converge on the middle.

3) In the middle of the house, I need to get in these steel posts that will support the ring beam that will eventually support the precast concrete ribs that will eventually hold up the steel arches and shotcrete that will form the radial vaults.

This weeks video is about setting up the posts for the center section.


The Video

The Story

I’ll put the story in here to provide a little more detail and to make it text searchable for Google ;^).

Working backwards:

In this region of the earth sheltered house, the load from earth above (not shown) is directed, by the radial vaults (made of heavy shotcrete over steel arches), down onto the precast concrete ribs.


On the outside edge of the house, these radiating concrete ribs (which weigh almost 5000 lbs each) are sitting right on 4’x4′ concrete pads made of strong reinforced concrete 1 ft thick.  However, at the middle of the house, the high end of these ribs are set into a central tower made of shotcrete (which will carry most of the final loads) over a steel skeleton (which will carry all the loads during construction before the shotcrete is in place).  This image also shows the QuadDeck ICF floor forms. When concrete is poured over these, it will help lock the steel posts into position.


The load of those 10 heavy ribs runs thru the ring beam and down the structural steel columns into the shotcrete basement wall below.


Tower_WallSurfaceThe 3D CAD model shows a nice flat surface where these pipes attach to the top of the basement wall.

The reality is that the shotcrete guys did not do a great job of squaring off the edge of this wall, probably because it was 9 ft tall and hard to reach. I needed to fix that.  I setup some cardboard forms to the level the wall should be at and backfilled with hydrolic mortar.  It was thin enough that it was pretty much self leveling.

The next step was to prepare the steel bases.  I bought a box of scaffold bases for $4 each, but the (nail) holes were too small to fit the anchors thru.  I drilled them out using the lowest setting on my drill press and some lubrication.

Drilling steel requires low speed and lubrication.  I lubricated with thread cutting oil.  The smallest container I could find was much more than I would need and only cost ~4$, the drill bit was 7$, so I used the lubricant generously in order to preserve the life of the bit.  I found applying it directly to the bit was the best way.  If the bit started to smoke, I would stop the drill and add more oil.  If the speed/pressure and lubrication are correct, long spirals of metal will come off.  This indicates that the steel is being cut and not just wearing away the bit.


RED_HEAD_SleeveAnchorThen it was time to head back out and mount the bases to the wall.  I was using sleeve anchors that require you to drill a hole first, and then drop the anchor in the hole.  It is important that the sleeve be completely below the surface. When you tighten the nut, the sleeve is expanded and presses against the sides while the nut pulls what ever you are attaching down toward the sleeve…   I was in a rush and didn’t put one of the first anchors in properly.  There was probably dust in the hole.  But I couldn’t pull it out again either.  With the sleeve too high, the nut tightened against it before pressing the metal to the concrete, so it would never be tight.   Eventually, it will be under another ft of concrete, so I was not too worried about it, but I put the rest in more carefully.

I was also careful to make sure each scaffold base was level so it would be easier to plumb the columns later.

My steel posts were ready a couple days earlier than promised (a first for me on this build), so I picked them up in my trusty trailer.  They weighed about 100 lbs each and put the trailer near its official limit, but it felt like it pulled easily.


The following weekend, my parents visited with my sister.

The mission was to move the steel posts into position on the base plates, hold them steady and level and then tack them into place with my welder.  The first one worked pretty well.   But the welder jammed on the second one.  I couldn’t untangle it, so we had to cut out all that welding wire and re-setup the machine.  From then on, I always checked the wire spool every time I moved the welder to make sure that it was not tangled.


This third post was the one on the less stable base, so we added extra bracing to keep it plumb until the concrete is poured around it.  We had a lot of experience pluming steel last summer, so everyone knew exactly what to do and it only took a minute or so.

My sister and I both enjoyed the welding, so we took turns welding vs holding… Some times on the same post if it was tricky to access a certain point.  The most time consuming part of the process was simply adjusting the scaffolding, etc. so we could reach what ever we needed to reach.


It took us about an hour to get the first 5 posts in, but they were on the side of the circle that was easy to reach.  We were expecting the back side, were we had to balance on the wall, to be more difficult, but it was pretty easy too.


After all the posts were in place, I was worried that someone may give these a good push and cause them to shift… Yes, they are welded to steel plates bolted into strong concrete with 3 inch steel anchors, but an 8ft long 100lb lever would probably be able to pry those out.

I wanted to weld the ring beam on right away, but each half was 320 lbs and I couldn’t think of a safe way to get them into position.


So we decided to weld some rebar between the posts as a temporary solution.  This was nice and easy and I really liked the look of it, so it will be sad to have to cut most of it off again when we need to put the door bucks in.


I was not sure how far my tank of shielding gas (Ar and CO2 for the MIG welder) would go, so we only did tack welds.  That turned out to be a good decision because it ran out just before we were done.  Without the gas, the final few welds looked pretty ugly.

After that, we put in some work prepping the shop for building the forms, and I will talk about that another time.

The next step in this center section will be getting in the QuadDeck ICF (insulated concrete form) floor over the basement.  I am having a painful time getting that scheduled.

The rest of the steel arches are still being rolled and I will soon start on the forms for the ribs.


Mid March Update…


Posted on March 15, 2014 by

Progress Update

Well, according to our Gantt chart (schedule), my wife started getting permits last week…  Except we are not actually there yet.  Instead we will be filing banking paperwork on Monday.  I don’t want to bother with the permits until the loan is approved.  And we were waiting on a tax return and an extra paycheck to beef up our funds before we applied for this year.  So, its a good thing I padded the schedule a bit so this delay shouldn’t affect the date we hoped to break ground.  I am still nervous about dealing with the mortgage company though.

Virtual Build

Things have been a bit busy at work and I am working on a paper for my “adult onset MBA”, so progress on the virtual build has been slow the past few weeks.

I did manage to get the Skylight curbs on. They look like industrial chimneys now, but they will be mostly covered in earth and that should soften them up.  I may need to adjust their elevations a little.   Originally, I had them over the showers.  I installed skylights above the showers in my current home and I really enjoy showering in the sunlight.  Of course, it would be a lot easier for someone to just walk up and look in the skylights of an earth sheltered home, so I will need to use frosted glass.  The architect moved them to the middle of each room (for symmetry).  But the virtual build revealed that I would need to cut central steel arches, so I moved them back.

I also worked a bit on the front of the house.  I got the steel structure up in the front wall and added the concrete sun shade to the front of the house.  It still has a long way to go.  For instance, I need to put the steel structure to support the concrete shade, add a bunch of roof structures and the front door is still missing.


One thing to note is the way the foundation dips on the right hand side…  This is the cost of having a basement that comes closer to that corner.


As we get closer to the build, I have been getting updated prices on things like the steel arches.  The price has actually come down some what.  Also, since I get charged “by the bend”, regardless of how long the bend is, I have adjusted the order so that pieces of the same radius can be bent as one long piece and then be cut to length.  That will save me some money.

I did find that the 5/8th inch thick steel support plates that the engineer specified in many locations are somewhat difficult to find.  All the steel suppliers I called said they would need to order that specially for me.  I had only needed a few square feet, and special ordering has some minimum area requirements which will raise the cost for me significantly…  Not sure what to do about that yet.

Do-it-yourself Electrical?

The biggest change to my sourcing plan was due to a conversation I had with an electrician two weeks ago.  He is out of the business now, but still licensed in my state.  He looked at my pictures and said he could understand why the bids were so high.  Electricians don’t want to figure out how to do my unusual house when they can just get regular jobs.  The FUD (fear, uncertainty and doubt) translate into a high bid.  But there were also real reasons why it would cost more.  They would need to use more conduit, need to more carefully secure the boxes, etc.

He suggested that I should just do it myself.  I told him that I was already planning on taking on too much of this build myself.  I have wired a few outlets and lights, but never something as serious as an electrical panel or a large as a whole home (or even a whole room)…  He said he thought I was smart enough to take care of it and I could save 3/4 of the bid price.  Anyway, I am seriously thinking about it and got several books on wiring and the electrical building code this week.  I do know some home builders who did their own electrical.  Perhaps, I will do most of it and hire someone to come out and give it a once over…?  At the very least, I can handle my own “finish” electrical.

We also attended a local building show this week.  It cost us $10 at the door, plus we bought some of those roasted nuts for $6 more…  Those shows are never really worth going to, are they?  We talked to a few people, but nothing really changed.


Well, I am up to about 2700 visits a month (over 5000 page views), which isn’t bad even if half of those are robots or mistakes.  This past month I had a couple interesting encounters on the web.

Comment on other sites?

First, someone on the the Malcolm Wells Yahoo group posted a link about Earth Tubes.  I jumped on it right away and found it was my page on Earth Tubes, but on another site.   It was the sort of site that has a number of revenue generating adds and the writing at the top of the page said “Written by David”.   They had done a full copy and paste, so the images were actually still on my site, but hyper-linked into place.  The site had no contact information anywhere on it, but using some Google search, I found a video related to the site.  Scrolling down in the YouTube chat, I found where “David” had a conversation with someone and ended up giving his email address.  From that I was able to find his google+ page and his LinkedIn page.  Eventually, I even found his mailing address (in the USA).  I emailed “David” and asked them to give credit where it is due.

While waiting for a reply, I looked around the site and found that pretty much everything was just copied from other sites, but all claiming to be written by David.  About 2 hours later, he wrote me back to say he was sorry and had added a line at the top with my name and a link to my website…  Oh well.

I saw another website (in Czechoslovakia) had also linked to my site and described it as a “very long, but detailed, overview of Earth tube design”.  I guess I need to work on being more concise ;^)

Comment on my site?

Of course, the opposite also happens.  I had referred to Larry Larson on my page about Earth Tube design.  However, while I gave him a “nod of the hat” as an expert in the field (literally since he professionally installs earth-tubes out in the “field”), I disagreed with his opinion that the tubes need to be corrugated and laid in a serpentine path to generate heat exchanging turbulence.  I also made some generally disparaging remarks about the use of corrugated HDPE pipe ;^).

Larry contacted me.

Actually, nothing too dramatic.  He just wanted to discuss my concerns.   He writes even longer emails than I do, but we had a number of back and forth email exchanges.  It may not be quite over yet, but I am still pretty certain that his serpentine layout is detrimental to performance.  However, I have softened on my critique of the corrugated pipes in general.  He argues that they win in terms of “bang for buck”, and perform well if installed well.  When I have the time, I will go back and adjust my text a little.

One good thing that came out of our exchange is that Larry is going to post some earth tube performance data on his site.  The data (which I am privileged to have already seen) shows the inlet and outlet temps and humidity of the earth tubes in his own home (in Iowa) over a 10 year time frame.  He showed me some graphs and they were pretty interesting, but the samples were taken by hand.  He said that my soil temperature experiment inspired him to get some small data loggers from Thermoworks and install them in his home and in some of the other homes that he installed earth tubes for.  Including one that has better performance than his own home.  He plans to publish the graphs of the inlet and outlet temps for each home every 3 months or so.

I also plan to adjust my plans a little and have a corrugated earth tube come into my new home “for experimental purposes”.  If it causes any problems, I will just block it off.  The delta cost will be small since I plan to use my drain tile for the job.


February 2nd


Posted on February 2, 2014 by

Virtual Build

Over the past couple weeks, I put in half an hour here and there in the evenings and moved the virtual build slowly along.  Of course, I would be thrilled to get this virtual build speed in the real world ;^)  Initially, the plan was just to illustrate the building process for various subs that would be helping.   I planned to just show the construction of the basement, central tower and how the ribs would be setup.  However, as you may have seen over the past couple posts, the virtual build has already helped find and solve so many problems that I have decided to press on with it.  I added the garage and I am currently working on the bedroom wing.  Next, I will work on the front of the house.

Virtual build as of Feb2nd, the garage, mezz and other areas are mostly complete, I am working on the bedroom wing and will work on the front of the house later.

Virtual build as of Feb2nd, the garage, mezz and other areas are mostly complete, I am working on the bedroom wing and will work on the front of the house later.  You can already see that this house design is very original.

I had been thinking a lot about how to lay out the ribs while I was casting them, I thought it might be a good idea to illustrate that with the virtual build.  For a long time, our plan has been to pour the garage slab early in the build, but only setup the rear of the quonset hut.  I could use the partial construction as a covered workshop in the back while I setup the rib forms on the front half of the slab.  Without the roof in the way, I could use a crate to lift the 4500lb concrete ribs up and over to where they would be set.

I had planned to make a left and a right rib form because it would save me needing to flip and polish the “back” side of one that would be exposed against an end wall.  I had already worked out (mathematically) that I could fit two of these on the slab in front of the partial quonset.

Gantt_RibsNow I was working on my gantt chart and considering how much time would be taken making these only two at a time.  I also considered how much extra cost would be incurred with the multiple crane visits (to set them up 2 at a time).  We had already planned to put a slab in-front of the garage (even if the rest of the driveway will be gravel), so the boys could play basketball.  I started considering the option of placing the slab earlier in the process  and building a few more forms.  Even if the extra forms cost an additional 600$ each, I could make 2 more and save on 2 expensive crane visits and a couple weeks of time.  I would probably at least break even on money, but save time.

There would be no additional cost to adding the concrete pad early since it was already planned for later in the process, but it may later be seen as “in the way” as construction equipment would need to be careful not to crack it…   

ArchForms_Layout1So, I added the ribs to my garage model…  You can see that it would be very difficult to fit a 3rd rib on the pad.  Yes I tried other configurations, but I need room for the forms around the ribs and space too work, and I couldn’t let them go under the quonset or the crane wouldn’t be able to lift them up without dragging them.  However, for the other ribs, I decided to make two left hand ribs and they can be put closer together…

Then it occurred to me that I needed to go back and reconsider my earlier decision about wanting to start with a left and a right rib to save time/money polishing (because one side would be placed against a wall.)  I decided that I would save more money and hassle with the more compact arrangement of same-side ribs.  In the software, it is pretty trivial to make the necessary changes and voila!  Four ribs in a compact arrangement on the one slab.



I will update the Gantt to show building two forms first, then working on the second two forms while the first two ribs cure…  Then I could position all 10 ribs in only 3 crane visits instead of 5.  Of course, I still need to polish the back sides of the ribs, so I will need to flip them over before I set them, but I can place them in the (soft) dirt for that and I think I can get that done with only one extra crane visit for the full set.  It seems like a plan for now.

Other revelations included that the steel stud layout for the bedroom was messed up by the architect (yup, I checked my original notes).  It was a classic symptom of 2D design where the various views, created separately, were not actually compatible or build-able.  I went back to check my original notes and sketches that I had sent in and they were correct, so I guess the architect just didn’t understand.  I will document that another time.  Lets just say my errata list is growing.


I have started hearing back from various contractors and the bids are looking much better.  I got a very reasonable excavation bid to go with my good footings bid.  I got bids on hooking up my electricity (a very reasonable $285 to setup the temp construction meter and then about $4.60/ft to run the permanent cable and setup for 400 amp service.  I am waiting on an electrical and HVAC update that should be in early next week.   It is clear that I still need to find a reasonable plumber bid (the 6 I got last year were all either too high or too un-reliable).

I also got prices on HDPE pipe for various diameters…   Trying to understand the pricing structure better, I divided the price by area, weight, etc. and quite reasonably, it turns out to be priced by weight.  $1.25/lb, delivered.  For 8 inch pipe with a 1/4 inch wall (HDPE 8″ DR 32.5), that comes to about $3.83/ft.  I need about 450ft for an earth tube loop, plus about 350ft for internal duct work in the house…  So that goes into the estimates.

Shotcrete meet

A highlight of last week (for me anyway; I am not sure how your week went ;^) was a meet with my most-likely shotcrete guy.  I have been talking to a couple other potential shotcrete contractors, but one is just not big enough scale and the other is not really sure about the whole earth sheltered concept.  At this point, I trust Nate more than the others and I think his prices seem fair.  The biggest problem is that he is hard to get ahold of.  It has been more than a year since we managed a meeting.   My project is just too unusual for him to quote confidently, so he had agreed to a time and materials quote, but I needed a better idea of how long he thought things would take and I still hadn’t got a quote on some aspects of the build, such as the specfinish on the inside.

I drove out to his place, which is about an hour from my current home and about 40 minutes from the building site (its a big triangle around Ann Arbor, MI).  He had a couple big friendly dogs and a nice sized kitchen table to lay the plans out.  I set up my computer and showed him my virtual build, my Gantt chart, etc.  My main goals were to make sure that the plan for the build made sense to a professional and experienced shotcrete guy and to get good numbers for budgeting purposes.   I showed him the virtual model and we talked about practical things like how to get the rebound (shotcrete that doesn’t stick to the wall and is, therefore landfill) out of the basement.   We talked about the possibility that some of the non-load bearing walls could be built hollow (or filled with insulation) and still covered with a thin coat of shotcrete to match the more solid walls.  We talked about hiring some of his guys to help tie the rebar (along with other tasks), and how quick they could work.  He even shared some trade secrets about the fastest ways to tie rebar, plaster walls, etc.

Along the way thru the virtual model, we kept referring back to the Gantt chart, which included things like the dates for each of the 4 shotcrete phases and the amounts of shotcrete that needed to be applied in each phase.  He factored in if  it was high work or regular walls (which he kept referring to as “money walls”), etc.  We discussed if the dates were good for him.  He was a bit concerned about the first shotcrete date because it was in May, which is prime swimming pool season.  The other dates are past swimming pool season, so he will be glad to keep his schedule busy.

We discussed equipment that I would need to rent and what his crew would bring (and the associated costs).  No surprises there except that he mentioned he would bring lots of scaffolding at no additional cost, he just wanted me to make sure the floor was level enough to move them around.

We discussed how much notice I would need to give to schedule his crew.

The main rough patch came when I got to the part about using his gunite machine to spray the specfinish along the underside of the vaults.  Nate did not want to do that.  Apparently, it is messy horrible work.  See this pic from monolithic.org where they create inflated fabric domes and then coat the insides with shotcrete to form the structure.  Note the full body coverage including saran-wrap on the helmet.  When the operators face gets covered, he can pull on the roll to get a clean section.  My plan had most of the shotcrete structure applied from the outside and only a very thin (3/8″) layer applied on the inside, but still…

Nate  said he would rather just have his guys apply the plaster by hand, but that sounds rough and slow to me.   We talked about other alternatives including spaying on the ceiling with a drywall hopper gun or having an acoustic ceiling company come in and take care of it.  I had already got a quote on acoustical ceilings, but my wife didn’t like the samples I brought back and didn’t want to consider it at the time.

20x20GlueUpTilesAnother option may be that I would use the same glue up styrofoam ceiling tiles that I planned to use to form (impress) the ribs.  It may look good to have the same pattern in the vaults between the ribs, but I am a bit concerned about fitting the square pattern to the curved and radiating vault shapes and it wouldn’t work at all in the compound curved bedroom vaults.

I left the meeting with a few notes on minor changes that I needed to make to the Gantt and process and some homework to Google search a number of things that were discussed (such as a rebar tie belt with a reel).  I also have the costs I will need to complete this portion of the budget.