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.
For the Video:
For the Story:
An inspection is needed before back-filling. Inspections in our township are limited to Monday, Wednesday or Friday, 10:00 AM to noon. And you are required (ideally) to give the inspector two days notice. Sherri and I had already got the waterproofing up and started the drain tile the weekend before, so on Monday, I scheduled the inspection for Wednesday morning and scheduled Roe Brothers Excavation for Wednesday afternoon. The plan was to complete the drain tile on Monday or Tuesday evening, but we had thunderstorms…
My sister (Bonnie) visited us from Canada again, arriving by motorcycle late Tuesday night. I am sure she was thrilled to hear that we would be getting up again at 5:00 AM. We had to get out to the property by first light in order to be sure to get the drain tile in before the inspector arrived.
Drain tile
They call it “drain tile” because it used to be made of clay tiles, curved like Spanish roofing tiles. Now days, it is much better to buy long plastic tubes. Special drain tile PVC is probably better to use because it has smooth walls and lays straight, but I used the corrugated HDPE pipe instead, primarily because of the price and because it is easy to lay around curved walls. I admit that the corrugations are not ideal if you want water to drain out of the tiles completely. I bought drain tile with a sock around it because it was only 5 cents more per ft (it is 50 cents more per foot with the sock if you buy it at Home Depot, so don’t buy it there).
Having to lay the drain tile is a little frustrating because, with all the sand on the site, drain tile is totally unnecessary. We have gone thru many storms in that excavation and have seen that water just falls thru the sand and the water table is not a problem. However, drain tile is required by code. A fellow builder in the same sandy area told me that he put in the drain tile to pass the back-fill inspection, but didn’t actually run it anywhere to drain. Even the building inspector told me that he doesn’t expect my drain tile will ever carry any water.
However, I am the kind of guy who likes to do things right anyway. I spent a lot of time making sure that my drain met the required slope all the way to daylight. This required a lot of digging to lower or raise the ground level.
The building inspector also insisted that we follow the building code requirement to cover our drain tile with 6 inches of pea stone and cover that with landscapers fabric. This would have been great on my current house which is built in clay… Research on the internet showed that it was best to lay the landscapers fabric down first, then lay the tube and gravel and cover it with the other half of the fabric like a very crunchy burrito. The truck delivering the pea stone couldn’t get very close because he was sinking in to our sand (irony?), so we had to carry 4 yards (actually only used 3 of them) down to the footing by bucket.
To make these drain tiles worth all the effort, I decided to use them as bonus earth tubes. This required a change in the layout. Instead of a loop around the house and a single tube draining to daylight, I made it a circuit with both ends draining to daylight… That took an extra hundred and fifty ft of tube that I will run down the same trench as the septic pipe. Actually, I took it one step further and connected the high end of the tubes into my house. Sherri thinks this is a terrible idea because the air traveling thru the tubes could be picking up mold from the corrugations. The fact that it passes thru the septic trench doesn’t help. I think it was fairly low cost and has minimal risk and I can seal it if she turns out to be right.
Back to the Story…
This lugging pea-stone was the fun part that Bonnie arrived just in time for. My wife and boys also carried their fair share of pea stone that morning. The work goes by quick in the timelapse video, but it took several hours in real life. Then we closed the landscapers fabric and waited for the inspector.
He arrived and took a careful walk around. I was expecting him to check the slope, but he seemed content with a visual inspection. I guess it was obvious that it dropped by a ft along the side of the footing. He did comment that my drain tile burrito was strange because most people just lay the landscapers fabric on top of the pea stone, not under it… We passed that part of the inspection.
Waterproofing?
The inspector was much more concerned about my waterproofing.
I didn’t want to use the stinky tar that is commonly used in my area. It is dirty and smelly and a pain to put up. Other “board based” waterproofing is expensive and much better suited to smooth flat walls. I ended up going with an “elastomeric penetrating sealer”. The install was covered in this post. This stuff sprayed on with a paint sprayer, but quickly soaked in and dried clear… Other than slightly darkening the color of the concrete, you can’t even see or feel it. At a microscope level, it has actually affected the chemical structure of the first quarter inch of concrete to lock out the water… And the elastomeric part will actually bridge cracks to keep them sealed (so they claim).
Anyway, I can’t blame the inspector for questioning a new type of waterproofing that he had never seen before (and still hadn’t really been able to see). He asked for literature on the waterproofing, specifically, if it had passed a certain test. I said I had seen the tech specs on line and they talked about this being for above and below grade waterproofing of foundations and basement walls. I could send him links that evening (in the mean time, Sherri actually got them on her smartphone while on site).
Meanwhile, I had a crew coming to back fill right after lunch.
The inspector decided to give me a “provisional” pass. I could proceed at my own risk. If the waterproofing turned out not to be acceptable, construction would need to stop until I dug it up and reapplied waterproofing so I could pass this inspection. Ouch. But I was pretty confident that basement waterproofing sold at Home Depot would pass. Surely, I couldn’t be the first person to try to use it? Dun dun dunnnn!!!
Back to the Story…
After lunch, the excavators arrived to back-fill. We had made it quite clear that we needed this fill to be well compacted because other footings will go on it. I also marked the 4ft level along the walls and told them to stop at that point so I could put in earth tubes and rigid insulation. They put the sand back in in lifts, each just over 1 ft, and then tamped like crazy with a mechanical tamper.
In this pic, I let my older son go in to help rake even though my wife was very nervous about him being down there while the excavator was running.
Earth tubes
Earth tubes have been central to my plan since the beginning. You can see these pages about earth tube design. So it felt great to finally be putting them in. It was also great to have my hard working (and digging gifted) sister to help me out. The primary earth tubes are 8″ double wall HDPE pipe that run over 250 ft down the hill to daylight. They cost about 6 times what the 4″ corrugated pipe costs, but they are stronger, have a smooth inside and 4 times the cross sectional area. The pipe I bought was “earth tight”, rather than “water tight”, just to keep the cost down.
We sloped the pipes at 1/4 inch per ft, which required digging into the freshly compacted sand. The difficulty of digging actually made me feel better about how well compacted the sand was. It took us past dark to get the work done.
This pic shows that we had to cut the pipe and join sections with 30 degree and 45 degree bends. Everything locked together without need for screws.
The next morning, we got Marty (from Roe Brothers Excavating) to compact over the earth tubes for us.
On the other side of the house, we put in shorter earth tubes (average 75 ft) between the house and the window well (as the low point). Here I experimented a bit. I did put in two more of the 8″ double wall HDPE pipes, but I also put in a 6 inch corrugated HDPE pipe and a 4 inch Corrugated HDPE pipe.
Last (and probably least), I put in a 1″ solid pipe (it was actually intended as irrigation pipe). I have had the opportunity to computer model a system for a researcher in India who is working with a system of 1″ earth tubes. His physical model is producing good results so far (he has asked me not to show his results until he publishes his paper). My biggest objection is that the 1″ pipe actually costs about the same as the 4″ pipe, but you would need 16 of them to get the same cross sectional area. There is also the issue of greater back-pressure thru smaller pipes. The benefit is supposed to be much greater surface area, and therefore better heat exchange, so you can use shorter pipes… I am looking forward to the conclusion of the research, but wanted to test my own.
I used hydrolic cement to seal the pipes into the holes I had made in the basement wall. I also filled the area around the connection with pea stone so that water couldn’t sit there.
Back to the Story…
Once the pipes were back in, back-filling and compacting proceeded as before.
At certain times, Bonnie and I laid down Foamular 250 rigid insulation to help trap heat in the volume of earth around the basement. I will talk more about that another time…
The back-filling isn’t completely done, first we need to finish the trench down to the septic tank, and then we can back-fill on that north west side of the house.
