Earth Sheltered Links
Here are a few new links to look at. There have actually been a few in Houzz lately, but I lost the specific links… Maybe I will find them again another time.
Kentfield House from Houzz.com
Messy Nessy Blogs about offbeat and unique things, including Earth Sheltered Homes. Here are two articles that were shared recently on the Malcolm Wells Yahoo group, but I think you can find more on the site if you dig around a bit..
This first one is about Englands abandoned Rock Houses. It appears that these homes were abandoned after hundreds of years of continuous use due to shutdown of the local industry. Many believe this underground villiage inspired Tolkein to include them in The Hobbit. The very old homes are still in great shape, although some are inhabited by endangered bats.
And this second one is about a hand-dug underground home and garden in California known as the Forestiere Gardens. The owner dug subway tunnels in NY at the end of the 19th century. He found the surface of Fresno to harsh (this was before air conditioning), so he started digging in his spare time. On his own, and without power tools, he dug out an estate of nearly 100 rooms, passageways and courtyards covering 10 acres.
This one is for a partially built earth sheltered home in California… This typical Terra-dome home is more bunker than beauty (to each his own), but the site is still interesting for seeing the construction process. Its also for sale, if you want to live in that area.
As you may recall, my design features pre-cast concrete arches to support the heavy earth loads and let me have open spaces without requiring large spans. I had some old posts about how these will be built, and even my own experiment to build quarter scale models.
I did get quotes on having these ribs done by professional concrete pre-casting companies. One even sent me nice faux stone concrete samples, but when the cost estimates came back, they ranged from $40K+shipping to $80K (with shipping) for the 10 ribs… I thought that was ridiculous considering that each rib only used about 130$ worth of concrete and less than 200$ worth of rebar. I asked the companies how many forms they would make and what they would make the forms out of… All three said that 10 was a small order, so they would just make 1 form out of wood…
Obviously, they were charging way too much and I was going to have to take this into my own hands… I had designed the ribs to be cast easily in a 1ft deep form. I could do this.
But first, I wanted to make a computer model to figure it all out.
My model revealed that the cost of reusable parts, assuming I went with a rather expensive Melamine base and 2 layers of 1/4 inch smooth plywood for the side walls, would be about $575. I would probably make 2 in order to cut down on crane visits (the crane will have to come at least 5 times with 2 forms). Then each rib would require about $350 worth of rebar, concrete, etc. I also decided that I would need to buy a concrete polisher (wet) ($200) and a sawsall concrete vibrator attachment ($50).
All told, that would mean about $1150 for the 2 forms, plus $3600 for the rib materials, plus $250 for tools, which gives less than $5000. If I add 20% to cover misc, it comes to $6000. I plan to work out a deal with the concrete company to rent their crane for a reasonable cost. They currently use it to place pre-cast septic tanks which are about the same weight (35 cuft at 130 lbs each is 4550 lbs, plus the weight of the rebar).
Along the way, I thought about things like layout, materials, form removal, etc. For instance, I plan to build these on the front half of the garage slab. I will build the back half of the quonset for use as a shop, and then cover the front half with a large tarp to keep the rain out. I can then remove the tarp so the crane can pick up the ribs more easily. I plan to use some #4 rebar to create hooks on the top of the casting. In order to remove the form later, I will need a slot in the form that I will plug with pieces of scrap insulation during the pour. For a base, I plan to use melamine sheets that will provide a non-stick surface. I will then need to polish both sides of the form to get a similar finish on the trowel finished side of the concrete. I plan to build two forms, one left handed and one right handed… There are a few different configurations to lay these out next to each other to minimize the space needed, I think I will go with a 24×24 layout that will require 5 sheets in the top layer, 6 in the middle layer and 1 in the bottom.
Here are some pics with a few more details…
Rib assembly. The brackets are screwed into the 2x# forms, which are bridged together with plywood scraps and all of that is screwed down to the melamine base… but the sidewalls are not actually screwed to the brackets…
A detail of the hanger. The PVC pipes along the spine will make it easier to set the vertical rebar and feature ridged insulation wedges. The PVC is held to the form by a screw which is removed before the forms.
Rebar skeleton, mostly #5 rebar tied together with #3 rebar loops.
The loops are mostly spaced by 8 inches, but the engineer specified that the spacing be reduced to ~4″ near the high end of the lower spandrel.
Closeup on the high end spandrel. You can see the PVC holes that will help tie the rib into the central tower.
Low end of the form. The white PVC pipe will allow the rib to slide over a 1″ steel post in the foundation. The green “hangers” are 2×6 boards that will keep the form from bowing and help me suspend the rebar skeleton.
Table to calculate costs of the forms and rib material
My soil temperature experiment has been running for over 2 years. It has been a long time since I saw anything new in the data, so I am not too worried about it any more, but I figured that every years temperature profile is different, so I might as well let the experiment keep on running until I build…
Last time I downloaded the data, I noticed that there was one bad sensor, but I was busy and since I didn’t really need the data, I didn’t worry about it.
Several of the wires had been damaged, probably by little teeth… This white wire is the biggest sensor on the station and includes air temp and relative humidity.
Prepping for this next winter, I went out to the property today to change the batteries and download the data. I also replace the burlap skirt that I had over the wires. I remembered that one of the sensors had given bad data last time, so I took a careful look at the wires and found that two had be severed and a couple more were chewed partway thru.
Could this have been prevented? Possibly. In some of the pics, you can see what is left of the original burlap that I had used to protect the cords. It had been worn away by the environment (sun and weather), and I had been too slow to replace it. Had I replaced it sooner, I might have prevented whoever was chewing on the wires from having access. “Stitch in time saves nine.”
I downloaded the data and took a closer look… Things were a bit strange (as the charts will show), so I decided to try the number-one IT trick “turn it off and turn it on again”. I changed the batteries and rebooted the data logger.
The black wire was for the 7.5 ft deep control temp. Behind it, a bit more out of focus, you can see another black wire that was nicked…
Back at home this afternoon, I see that the data showed the 7.5ft deep control temperature probe (black wire) failed on June 6th, 2013 at around 5:30 PM. Instead of turning off and not giving any data, the sensor showed ridiculous numbers in the -90°C range.
In the middle of the night on September 6th, three months later, the air temperature and RH data (the white wire) went horribly wrong. Suddenly air temps appeared to drop from 12°C down to -91°C and relative humidity went from 93.9% to a nonsensical, but consistent, value of “1”. I don’t know why, but the air temperature fluctuated, so I guess some electrons were getting thru.
This chart shows the sudden drop in the air temperature data, along with subsequent fluctuations.
The data started getting strange lately…
Then something else strange happened… Shown as a blue vertical spike in the previous chart Not sure what, but on Oct 10th, the data suddenly went crazy… Perhaps the data logger hiccuped? Or the battery failed for a moment? Or maybe a deer peed on the station? I probably will never know, but this next chart shows the raw data around that time.
Raw data from my sensors showing the strange hiccup…
The data goes crazy for about 8 readings, but then things seem to reset. After the reset, everything seems to have shifted down a bit… The strangest thing is that the 7.5 ft deep temperature sensor and the air temperature and RH sensors started making sense again (see columns H, L and M, before and after the hiccup). I can’t think why the data would start making sense with the wire still cut… perhaps there was data in the cache and it is showing me samples from a previous year? Anyway, when I saw this, I was glad I had reset the system while I was out there today… Hopefully things will look better next time I download the data.
This next chart shows all the temperature sensors, but I removed the 8 really bad readings from the above chart… You can still see the sudden shift on October 5th, as well as how long the 7.5 ft deep gauge was misbehaving… You can also see that everything returned to “normal”, but shifted downward a bit.
Fortunately, I had already determined that there was hardly any difference between the dry and control temperatures at 7.5 ft deep, so I won’t miss that sensor too much… But I will need to get out there and repair the other sensor when I get a chance and see if the probes appear to be trustworthy again after their reset.