So the year is over. It didn’t exactly go as I had hoped, but we are definitely in a better position to build next year than we were a year ago, more on that in my January kick off post. It is a bit frustrating as I put off doing other things because we expected to build, but such is life. This past month, I took things pretty easy. I only called one person for a quote (a very reasonable sounding plumber that I will bug again in January), and I put some time into building the home virtually.
Virtual construction is a way to run thru the process of building without the huge expense. I individually model each stud, track, buck and ICF piece and then assemble them as I would in the actual construction. Along the way, I am thinking about sequencing and other assembly problems. I try to build to the plan, but make notes when I need to make changes so things will fit. Of course, the computer could make things a bit too easy, for instance, I could just array my studs along and have perfect spacing. Instead, I tried to build things more manually by inserting and positioning each piece.
The below image shows the first steps of my basic construction plan.
I would start by pouring the footing, which includes a lot of precise layout, rebar, form work, etc. Actually, once that footing is done, I will be much more relaxed for the rest of it. I would then set the track (curved or straight) for my steel studs into the top of the footing with Tapcon screws. Then I would place wooden window and door bucks to guide the spacing of the studs. The Marinoware steel studs and steel frame jambs would be set (plumb) and screwed into the tracks. Flat straps are screwed to the outside of the studs to increase the rigidity of the assembly. Metal lath is screwed to the inside of the studs and track, partially to add rigidity, but mostly as a curved backing to catch and form the shotcrete.
- Basic construction detail
Along the way, I spent a lot of time figuring out steel stud placement. I am planning to use “balloon framing” so that load bearing walls will line up and I won’t need to spend as much time or money on laying the curved track. Since the steel studs will just be fancy integral formwork, I don’t need to follow strict structural guidelines. Instead of 2ft or less spacing, I can go a bit wider and not need to cut as many studs for windows, etc. I can vary the placement of the studs to line up with windows and doors across the various levels. For instance, there is an opening directly above the basement opening (shown above). If I shifted the main floor opening by a few inches, I could use one long steel frame jamb instead of needing to place two. I could also align the guest bathroom door with a mezzanine window buck and simplify the framework there also.
After all the steel studs, rebar and conduit are in place, with metal lath to keep things stiff and catch the shotcrete, we would shoot the basement walls 8 inches thick. Since the steel studs are 4 inches deep, this would leave 4 inches beyond the studs. The rebar, just outside of the steel studs, would be nearly in the middle of the wall.
Even though many of the steel studs go thru 3 floors (balloon framing), only the basement shotcrete would be applied in this phase. The top of this shotcrete wall would be cut/troweled roughly level six inches below the floor level. We may even be able to set the column base plates in before the shotcrete sets completely. We would then setup the steel columns and ring beam (I will need a crane of some sort) that will later support my concrete arches. I may do a little MiG welding to tack things in place at this stage.
This assembly looked fine at first, but I later discovered that the ring beam intersected the door buck by several inches. This was a mistake I had not caught earlier. I decided the best fix would be to notch the ribs… These thumbnails illustrate.
The floor system I have chosen uses ICFs (Insulated Concrete Forms) to support the concrete (instead of the wooden subfloor the architect/engineer specified, so yes, I will need to get this stamped by an engineer at some point, I was quoted $800 for that). These QuadDeck ICFs have light steel joists built-in to reduce the number of temporary supports needed. The ends will rest on the shotcrete walls with an inch or two of polystyrene overlap (roughly cut with a hotwire) and be tied in with bent rebar pieces.
This next image is a detail of the rebar (shotcrete and other details are not shown for clarity). Horizontal rebar is wire tied to the outside of the steel studs and should increase the stiffness of the formwork. I considered threading it thru the holes, but that would probably be quite a hassle. The vertical rebar is wired to the inside of the horizontal rebar, but with 8 inches of thickness, there is some flexibility here if needed. Rebar is placed before the shotcrete, and then some pieces are bent down into the ICF channels as needed. More can be added later and bent upward if necessary. I anticipate some issues in certain locations where the QuadDeck spacing clashes with the steel stud spacing, but it should be manageable. I also considered/modeled rebar placement between other ICF sections.
After the ICF forms are placed, they can be walked on. The electrician and plumber should appreciate how easy it is to set conduit and piping into the ICF decking. The ICFs are about 7 inches deep and we will be adding 5 inches of concrete on top of that, so there is plenty of room to work. We also plan to lay radiant flooring across the top of the ICFs. There are little plastic clips that screw into the polystyrene easily to support the radiant tubing. We will screw a form to side of the wall to contain the poor. It will only need to support 12 inches of concrete, so it shouldn’t be a problem.
Some of you may need a cross section vertical to understand the quad deck floor properly… Here it is. Basically, the ICFs form the “negative space” so that the concrete forms a nT (like a single or double-T, but continuous) beam across the spans. Where we meet a wall, the ICF is cut away so the concrete rests on the wall (tied in with rebar not shown here). On the left side of this example, I have cut away some of the ICF in order to create a concrete cross beam above the stairs to the basement. After the concrete is poured, the ICFs remain to provide insulation against heat and noise. They will ensure that my radiant heat goes up.
Now that there is a floor to walk on, additional studs, conduit, bucks, etc. are added in preparation for the main floor shotcrete. Since many studs penetrated from the floor below, this additional work is just incremental. I have not modeled it all yet, but it will include the fill walls under the ribs, the walls around the spiral stairs, etc. Once these walls are up, I will want to model the arches across the donut vault, the hop across the basement stairs, etc.
Here is a final look at how far I got during my Christmas break…
This process has been interesting so far and has resulted in a number of small changes. For instance, I noticed that the original plans placed the mezzanine windows such that the east one was right up against the east wall. When I built the 3D model, I placed the stud so that it would be at the surface of the 8 inch thick wall, but realized that one of the 12 inch thick ribs actually intersected the studs supporting the window. If I wanted to build the balloon wall before placing the ribs, I would need to move the stud by at least 4 inches to clear the rib. I also planned to put in a 14″ sun tunnel thru that corner to bring daylight to the guest bathroom, and that would also have passed in front of the window… So I decided to move all the mezz windows over by 16 inches. Since the steel studs were also framing main floor and basement doors, those would also need to move (to keep the steel stud layout simple). In the computer, this was much much easier to fix than it would have been if I had discovered the issue during the actual construction.
Similarly, I decided to lower the basement egress windows by 6 inches, I added a door way in the basement, etc.
Well, hopefully Sherri and I will love our underground house. “We don’t like our underground house” was the title of a blog by MizBejabbers who wrote about the pitfalls of her underground house.
MizBejabbers’ earth shelter in Arkansas. Check out her site for more pics, but this was the best one ;^(
Miz tells about how they moved into an earth sheltered home 18 years ago (built by TerraDome for a previous owner, who may have covered up the problems to sell it) and how it has not lived up to the earth sheltered promise. She writes about how it had all the fears (leaks, mold, etc.), but without the benefits of energy efficiency. She also talks about increased construction cost, severe depreciation, pests (bugs, rats and nosy people), etc. She does have a section on “happy things” such as feeling safe during storms, enjoying the peaceful quiet, etc. but concludes that these were not worth the pain.
She even blogs about mini tremors, which she thinks are earthquakes cracking the house, but I suspect it is the house cracking and settling as the soil underneath is slowly eroded. No earthquakes required.
For someone like me who is considering a similar investment, this could be a blog from my future, so I read it very carefully…
My conclusion was that this house was just designed and built really badly and in the wrong time and place. By time, I mean that it was built in the early 1980’s when few people had worked out how to do these properly. Lets go thru the issues, as far as I can tell from the blog.
The site: This house is set below the road on the side of a large hill overlooking the Arkansas river. The U-shaped design that Miz mentions sounds perfectly designed to catch all the surface runoff from the hill above and funnel it toward the front door. What is probably happening under the ground is even more threatening… Hills do interesting things to water tables and an earth sheltered home may be sitting in an underground aquifer, like a wet pebble in a stream. Try a quick Google image search for “artesian well diagram” if you are not familiar with the concept. Miz acknowledges that the french drains are not sufficient in capacity or well placed to drain water away before it enters the house.
Our site doesn’t have such a majestic view, but it is on the top of a hill, and our hill is very permeable sandy loam that will dry out nicely. Before I bought my land, I walked around during a thunderstorm and made sure the water didn’t collect or run. After buying the land, and looked “deeper” and buried moisture sensors more than 10ft down for my Soil Temperature Experiment.
The construction:In the comments after the article, she mentions that the house was built on fill (to make a terrace on the side of the hill). If there was water flowing down, around and under her home, fill soil would wash away more easily and would lead to further settling and cracking and leaking. My home will be built on undisturbed soil with a high compression rating and no erosion threat.
She also blames a “bad batch of concrete” for the living room roof crumbling. I am not sure if that was really the problem (or if the bad conditions just wore down otherwise adequate concrete), but The TerraDome homes are monolithic structures which are poured into proprietary modular forms. If the concrete is not carefully mixed and poured, there is no good way to fix it later.
My home will use shotcrete, which (when done right) is considerably stronger than any poured concrete because of its lower water content and the way it is compressed as it is shot onto the wall.
Miz mentions metal ducts rusting and falling apart, I will be using only HDPE ducts that will never rot or leak. We also plan to heat our home with radiant floor heating, a method better suited to the heavy concrete construction. We will still have ducts, but only for ventilation and de-humidification.
She mentions drywall rotting and molding, internal wooden walls being eaten by termites, etc. we won’t have any of that in our all concrete house with a specfinish gunnite surfaces.
The waterproofing: TerraDome, like other earth sheltered builders (including Formworks) with “proprietary systems” does not use a waterproofing umbrella. Instead they insist on more traditional methods used for waterproofing regular basements, glued or sprayed directly to the walls. These include bentonite clay or a “tar modified polyurethane elastomer applied as a liquid”. These directly applied methods are pretty useless if the concrete cracks more than 1/16th of an inch. Even applying something like a pond liner right over the concrete before backfill is not as good as an umbrella (away from the concrete) because it can be torn by the movement of the concrete and does not help with thermal mass.
Applying the waterproofing and insulation directly to the structure also excludes the surrounding thermal mass and allows water percolating thru the ground to strip it of its heat, both of which reduce thermal performance when compared with an insulating umbrella.
It also sounds like the soil around this home was not properly drained. The French drains mentioned are not well placed or of sufficient capacity to handle the location on the side of the hill. This moisture increases the weight and lateral (hydro-static) force on the walls. Cycling moisture levels are even more damaging.
An interesting side effect of applying the waterproofing directly to the structure, and then draining around it, is that you need to make a choice about the moisture level of the soil above the water proofing… Do you want it to be dry for the structure beneath or do you want to keep plants living on the surface? It is difficult to have both. Miz ended up shutting down her sprinkler and letting her plants die. Eventually, they had to remove the covering soil completely. The umbrella solves the problem by requiring that you drain only the soil under the umbrella and allowing you to maintain the moisture in the soil above.
My home will use an umbrella with three layers and I plan to go overboard on the french drains under the umbrella. It also helps that my soil is very permeable.
Conclusion: I think I can avoid the problems shown in this blog, but I need to keep my eyes open and be as careful as I can. I am sure the builder of this home didn’t expect these problems… And neither did poor MizBejabbers when she and her husband bought it.
Caveat Emptor! Buyer beware! When buying an earth sheltered home, you must be doubly careful to check it out before buying.
What is the latin phrase for “this may be harder to sell?” There is always some mistrust between the seller and the buyer, but this gets worse when the item, your earth sheltered home, is difficult to inspect, because it is buried, or difficult to compare, because it is unique or custom built. Economic Game Theory would suggest that because the seller knows much more about the house than the buyer (informational asymetry), he would only be willing to sell the home at a deflated price if the actually thought it was worse than the buyer thought. Sellers who’s homes have no issues would be less likely to sell for less than they thought the home was worth. This would reduce the percentage of good earth sheltered homes on the market even further. Buyers could deduce this and realize that a large portion of earth sheltered homes on the 2nd hand market are likely being dumped by their owners. Therefore, sellers would be willing to offer even less. This is why earth sheltered homes tend to suffer heavier depreciation than other homes even thought they should last longer. Blog articles and anecdotes and even random experiences with cold damp basements only make it worse.
If you want to prevent or at least reduce the depreciation of your earth sheltered home, just in case you ever need to sell, you can do things to reduce the buyer’s doubt. I will start by taking detailed photos of the construction. I also plan to bury sensors (temperature and moisture) and keep good long term records. Other maintenance and utility records also help to establish the efficiency of the home. Not painting, or other wise covering, the inner surface of the home will also help to preserve trust during the sale process. The effect of these efforts would be similar to the effect of selling a used car and including a full set of records; including gas mileage for every fill-up, maintenance records, a car-fax report, etc. Increased buyer cconfidence will translate into higher offers. Of course, it only works if you actually build a good earth sheltered home ;^)
The blog mentions their attempts to enforce a warranty or get money from TerraDome or the builder, or the previous owner, but all failed. I don’t expect to get a warranty and I will have no one to sue but myself, so I will need to select the builders carefully and make as sure as I can that the concrete mix is a strong one.
Mt Hartman Bay Estate
Hey all, I saw something fun recently…
Obviously the tropical location and ocean views are fantastic, and I love the tropical color palette and organic feel.
But what caught my eye is the roof line with its dormers… Check out slides 3 and 5 in the web gallery. There are some big differences from our plan, particularly in the scale and proximity of the dormers, as well as the depth of the earth. But this is the first time I have seen this idea (dormers in a forward sloping earth sheltered roof) used anywhere else. Too many earth sheltered homes are only earth sheltered int he back and display a large flat wall, made even taller by the height of the parapet wall, on the front. Some try to improve the front elevation by hiding the parapet with a mansard roof. I much prefer the way the forward sloping earth puts the green roof on display.
Dormers on a forward sloping earth sheltered roof… Our dormers will be wider (a product of my roof structure) and more buried, but the idea is similar.
This is the inside of one of those dormers, very modern and spacious… My roof won’t be high enough to fit a second floor, but I might put in a balcony in the back of the playrooms with closets below ;^)
They also have planted terraces, which is something we will have on the north west side of our house. And the below picture shows a glimpse of the water management system on the top left.
Check the websites for other views of the terraces.
Sherri pointed out how they used prickly things instead of fences to keep people off the edge. This next pic shows that well.
The rest of the slides in the gallery are pretty nice also. You can get a closer look at the water management system on slide 6. Slides 15, 25 and 29 will make you want to earth shelter.
Check out the “Suites” gallery to see inside the rooms.
You can see the stiffening members in the dining room roof.
It is a hotel and you can stay in on of the “cave suites” for 259$/night… I am sure the helicopter and yacht are extra.
It also looks great lit up at night…
This assembly looked fine at first, but I later discovered that the ring beam intersected the door buck by several inches. This was a mistake I had not caught earlier. I decided the best fix would be to notch the ribs… These thumbnails illustrate.
Now that there is a floor to walk on, additional studs, conduit, bucks, etc. are added in preparation for the main floor shotcrete. Since many studs penetrated from the floor below, this additional work is just incremental. I have not modeled it all yet, but it will include the fill walls under the ribs, the walls around the spiral stairs, etc. Once these walls are up, I will want to model the arches across the donut vault, the hop across the basement stairs, etc.
This process has been interesting so far and has resulted in a number of small changes. For instance, I noticed that the original plans placed the mezzanine windows such that the east one was right up against the east wall. When I built the 3D model, I placed the stud so that it would be at the surface of the 8 inch thick wall, but realized that one of the 12 inch thick ribs actually intersected the studs supporting the window. If I wanted to build the balloon wall before placing the ribs, I would need to move the stud by at least 4 inches to clear the rib. I also planned to put in a 14″ sun tunnel thru that corner to bring daylight to the guest bathroom, and that would also have passed in front of the window… So I decided to move all the mezz windows over by 16 inches. Since the steel studs were also framing main floor and basement doors, those would also need to move (to keep the steel stud layout simple). In the computer, this was much much easier to fix than it would have been if I had discovered the issue during the actual construction.
