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.
Response to Septic System
Andrew says:
Hi Simon,
Just to say I’m really enjoying watching your build process from across the pond. We are looking to do something similar (well, earth sheltered at least) in the UK shortly, so watching all your activity is very useful.
I may have missed it elsewhere, but can I ask what your build budget currently is looking like ? Ideally we are hoping to get to about 700 UK pounds per square meter for a 280m2 concrete build, but lots of people are telling us that that’s not realistic. I’ve done the budgets, and can’t see why it shouldn’t be though. Maybe I’m being naive or missing something !
What do you reckon in terms of a cost per square meter (or sq. foot) for your project ?
Anyway, best of luck as things progress.
Andrew
Simon says:
Hey Andrew,
People tell us to expect any custom home to cost about 150$/sf in our area, this is because they are “one of” builds and usually go with more expensive details. Tract homes (built with an assembly line and with all the cheapest fixtures and details) come in at about 86$/sf (according to the government data).
However, it is not really the square feet that bring in the cost (although they contribute), it is the finishing. Our home has no drywall, not paint, less than 200 sqft of wood floor, etc. We don’t plan to have a very fancy kitchen or budget busting doors or lighting. Concrete is actually pretty affordable, etc.
My initial estimates were pretty low based on “average” costs I found on the internet. However, the prices went up considerably when I showed average contractors my unusual plans. Some contractors admitted to tripling their usual per sqft estimate just to cover the unknowns. I didn’t hire anyone who tried to gouge me and ended up planning to do more aspects of the construction myself. So, after getting actual bids/estimates on all the elements of construction (some of which I planned to do myself) and adding 10% for overages and a few more percent for financing costs, it still came to under $100/sqft. Since then costs have occasionally come in higher than the initial estimates (it is hard to get anyone to commit to a fixed bid on an unusual project), so maybe we will end up above that.
Bottom line is that it should be possible build an earth sheltered home for about the same as a regular home. You will put more into the footings, insulation and waterpoofing, but can save money on heating system, roofing, flooring, and finishing (if you want to). You may also be able to argue that your operating costs will be lower, which is relevant if you imagine that as savings or simply as allowing you to afford a larger mortgage.
You may be able to build much cheaper than an above ground home if you used something like Quonset huts for the formwork… If we did that, I think we would be done by now.