After digging the trench and laying the septic pipe, drain tile and earth tubes, it was time to backfill the trench. We started at the top by the house, but I didn’t record the first couple hours for some reason, but I caught enough of the rest to put this video together.
The Video
The Story
We placed the earth tubes by staking them into the side of the slope. This saved us from killing ourselves manually back-filling the trench on what turned out to be the hottest day of the year. However, it did slow down the back filling process. Instead of just pushing the dirt back into the hole, we had to carefully (and manually) backfill around the earth tubes so they would keep the right position and slope… I guess this added another couple hours of backhoe time to the true cost of the earth tubes.
I was actually surprised how the excavator attacked the problem. I guess I naively thought he would bring the dirt in from the side where the dirt had been placed… Instead, he started from the other side and dug his way down. He dug undisturbed dirt and put it in the hole under and around my earth tubes. Once the tubes were covered enough to protect them from the excavator and there was a slope for him to climb down into the trench (in the video, you can see him slip a little), the excavator was able to reach up and pull the sand from the far side, down into the trench. From there he was able to quickly move up and down the length of the trench pulling in the dirt.
Eventually, when the trench was almost full, he was able to climb out the far side and reach some of the other dirt.
At some point, Dick parked the excavator and got into the bulldozer to level off and “reshape” the hill.
At this point, the Septic field is not yet complete, so there will still be some more earth moving before the septic system is complete.
My Pink Skirt
Marty and Dick knew I wanted a flat area 4 feet up the wall to put an insulation skirt in, so they flattened and tamped the ground in that area for me.
Meanwhile, I had been doing my own work for my employer in the trailer, but when they guys took their regular lunch break at noon, I started my 1 hour shift.
The idea is trap a bubble of heat around the house with an insulation skirt or umbrella. This idea was popularized by John Hait who calls it “PAHS” or Passive Annual Heat Storage, but the idea had been fully researched by the University of Wisconsin several years earlier. You can read more about it here.
The umbrella is really supposed to be several layers of insulation with layers of plastic between. I only put in one layer of 2 inch Rigid insulation (Foamular 250) and ran it out about 16 ft (2 sheets) from the house. Since this is really more of an insulating skirt beyond the basement rather than an umbrella over my home, I didn’t feel the need to go the full 6 inches thick that I plan to over the rest of the house. Similarly, I didn’t feel the need to put several layers of 6 mil plastic in this location. Instead I just went with one layer of pretty think painters plastic. The point of the plastic is just to reduce the amount of water that can go thru this area and steal away the stored heat with its high specific heat capacity. I sloped it all way from the house and covered it over.
I will eventually overlap this skirt with the larger insulating umbrella. Our backyard patio will eventually go over this area.
While the trench was open, it was our chance to lay the drain tile and earth tubes. We didn’t set the timelapse and we were too busy working to take many photos, but it is an important step for any earth sheltered home, so I want to capture a few details. Sorry, no timelapse.
We had already laid the drain tile and earth tube close to the house as we back-filled that portion. Click here for that story. But we still needed to run long tubes from the house to daylight.
The bottom of the trench was already sloped to 1% and the septic line, made of 4″ schedule 40 PVC, was already in place (done by the excavator and already approved by the plumbing inspector). We needed to bury it, but with a constant slope. Sherri and I used shovels and rakes to pull down dirt and bury the original line by about 6 inches. We (and the boys) stomped on this layer to pack it down, especially next to the buried septic pipe. The end result was a nicely sloped flat bottom trench.
We connected 100 ft long segments of 6″ corrugated drain pipe to the ends of the pipe we had already buried up by the house. We used a proper fitting connector piece and also taped it heavily and covered the connection in landscapers fabric. We laid these two parallel drain tiles along the trench and periodically placed dirt on them to even everything out and keep them separated by a couple feet. I would have liked to have separated them by more, and I did where the trench was wide enough. In all, we added about 150 ft of pipe to each end of the drain tile loop.
Normally, a drain tile loop is connected to a single long pipe that runs to daylight. However, by connecting each end to its own pipe, I am able to use it as an earth tube circuit with an inlet and outlet or two inlets. The other end of the pipes goes into the house, but I can simply connect those ends together if I want the air to circulate under the mass of the house without entering it (by-passive annual solar heating). The extra cost is the additional 150 ft of pipe, which cost me about ~$100.
The second layer of earth tubes was the 8 inch double wall (smooth inside) HDPE pipes. These come in straight 20ft segments that have a bit of flex to them. You can connect the pipes directly (bell and spigot ends with soil tight connectors) or you can connect them with 30 or 45 degree joints. It was a hot day and we did not have the energy to properly bury the 6″ corrugated drain tile before laying the larger earth tubes, so we decided to mount the larger earth tubes to the side of the slope (with stakes) a couple feet above the previous layer. This still left more than 10 ft of earth above these pipes for most of the distance and gave us more than 6 ft between the two parallel pipes.
At the end of the day, we had 4 earth tubes, each over 150 ft long, going from the house to “daylight” along the trench.
The next step would be backfilling.
Later, while back-filling the trench, we made sure that the 8 inch pipes stayed in place while the excavator back-filled below/between them and the 6″ pipes… This took some care and probably added at least an hour to the back filling process. The excavators charged by the hour, so that should probably be counted in the cost of the earth tubes, but seemed like a bargain compared to backfilling that trench manually on that hot day. I did pull out some of the stakes when they were no longer needed to hold the pipe still, but many were buried in place at an additional cost.
The step after backfilling around the basement was to dig a trench over 150 ft long and up to 15 ft deep from the house to the septic field location.
The video:
The story:
Again, I hired Roe Brothers Excavating. All the septic field bids had come in very close. Roe Brothers were not the cheapest, but I liked working with them and they had the right equipment (excavator vs backhoe). The trench didn’t count as part of the septic field bid, so I knew I would be billed by the hour. The right people on the right equipment can get things done more quickly and cheaply.
They started the process by finding the height difference from the excavation on one side (the back wall of the house had not yet been backfilled) to the septic field on the other. There was barely enough difference to cover the distance between the two points at the minimum slope (1%), and there was a lot of dirt between the two points. They laid out the shortest path and figured out how to dig it so the dirt would end up in the right place… Then they got started and I turned on the cameras. Excavation is hard on the land… I began moving all the nicer trees that were within the area designated for the septic field, including several that we had planted a few years before. I asked Dick Roe to spare the Oak tree on the one edge of the trench and the ash tree on the other… The ash tree didn’t make it. 
We also found some turtle eggs (they just rolled down the side of the trench from somewhere), so we moved them to a safer location. Weeks later, we found at least one little snapping turtle, you can find that pic on our facebook page. 
The trench got pretty close to my fathers pop up camper. I kept texting him scary photos just to make him nervous. 
The process ended up taking several days and included a pluming inspection from the house to the first tank and then a septic inspection beyond that.
Complications included finding a 75 year old garbage dump at the south east corner of the septic field. The guys called me down and told me they would need to call the health department (they manage the septic field inspections) and report it right away. The idea was that it would go better for us if we reported it and adjusted the plan accordingly rather than have the inspector find the problem themselves and have us undo our work. The health inspector required some changes the design of the septic field, including digging out and refilling the trash heap. This increased my costs a little. We also had more than one weeks delay due to a shortage of septic tanks and after those were in, we had another weeks delay waiting for the 60 yards of gravel to be delivered. Fun details.
In the end, it looks like we will end up about 30% over budget for the septic system (trench, tanks and field), and it is not quite done yet (more than one month after starting the trench) because the excavators had to move on to other jobs while we waited for the final inspection. Based on digging in the gravel, I would guess the inspection is passed now and the excavators will be back soon to finish up.
