Laying Out Grey Water Planters and Plumbing for the Earthship

This last week has been challenging; we have been laying out the grey water planters and the bathroom walls along the south face of the earthship.

The challenge has been laying out the planters and walls while making sure we still have space for kitchen counters, walkways between the rooms and everything that has got to go into the bathrooms.  This process has involved a lot of discussion and some arguments.  Sandra and I are both still alive so I guess the arguments were not too bad.

Before laying out the planters we needed to establish a direction of water flow and planter elevation.  I did not give a lot of thought to the flow of grey water through the planters when drawing the plans.  I did locate the bathrooms along the south face as I felt this would simplify the grey water layout and I think that was a good decision.  Our earthship has two bathrooms though, and this  means we considered two options for water flow; a split system terminating in the same planter, and a shared linear system.  In the split system the kitchen and common bathroom grey water would flow through two shared planters and the bathroom off the master bedroom would flow through its own planter before ending in the same planter as the kitchen and shared bathroom.  The split system was my early favourite as it meant short runs from the grey water sources into the planters.  I was quickly overwhelmed by the complexity of laying out this system.  Not having planned for this idea from the start it was hard to fit our planter layout into a split system.  We settled on a linear system that starts at the east and of the building and flows to the west end.  This system means some longer runs than I had hoped for, but it is fairly easy to understand and design.

The other consideration in laying out the planters was elevation; both with respect to all the other planters in the system, and in relation to the grey water appliances that are feeding the planters.  The appliances feeding the grey water system (sinks, tubs, …) must be elevated above the planters (you need about 1/4″ of elevation per 1′ of horizontal travel of the grey water pipes).  In our case it means one to two steps going up into the shared bathroom so that we get sufficient elevation to get the tub water to the start of the planters.  Also, each succeeding planter in the system must be slightly lower than the one before it so that water flows through the system (like an underground river instead of a stagnant pond).  Again, we sloped the bottoms of the planters approximately 1/4″ per horizontal foot of travel.

The planters are linked together with pipes located about six inches off of the ‘floor’ of each planter.  This means that the 1st planter is connected to the second planter by a 2″ diameter sewage pipe.  The pipe leaves the first planter with the bottom of the pipe about 6″ off the floor of that planter and enters the 2nd planter again with its bottom about 6″ off of the floor.  This means that the pipe also slopes 1/4″ per foot of horizontal travel to encourage the flow of grey water between the planters.  The pipes are located close to the planter bottoms so that the grey water elevation is constant in the system … no one planter is a swamp or dry.

We ran these connector pipes a year ago when we did the initial excavation of our planter space.  We used our backhoe to dig a trench along the front of the building.  We did not give a lot of thought to the size or elevation of our planters at that time … we just did not want to be hand digging the planters a year later.  Our ground is clay and rocks … making it pretty tough digging!

Because we did not set elevations or think through the size of the planters last year we have spent a lot of this week DIGGING BY HAND (I am very glad James is here).   We had to re-grade the planter ‘floors’ so that they all consistently slope a 1/4″ per foot, and we had to dig up all of the pipes and set them properly as well.  Most of this work is done now except for the last planter on the west side of the building.

We have also started forming the walls of the planters.  Again, the work we did a year ago digging the planters was not very accurate.  Most of our initial holes were wider than the intended planters.  This means that we have been forming pop can/concrete walls from the bottom of the planters up to our desired planter wall height.  Ideally, we would have been able to start the walls on the outside perimeters of the initial excavations, reducing the work and materials required.

Underneath the pop can walls that form bathroom walls we placed a small concrete footing (6″x6″).  Underneath the pop can walls that form planter walls we excavated a small trough and filled the trough with concrete before laying cans.  The footings contain engineered fibres and is a standard mix (1 part cement ; 2 parts sand ; 3 parts gravel).  None of these walls are load bearing; the purpose of the footing is to create a flat, level working surface for the walls.

All in all it has been a productive week!

DC Branch Circuit Notes for the Earthship

We have always planned to use DC LED lights and some DC appliances in the earthship.

I have been scratching my head a lot trying to figure out wire sizes for these branch circuits.  The lower voltage in a DC circuit means higher currents have to be allowed for in these circuits and larger wires must be used so that unacceptable voltage drops do not occur.  The following image is a screen snapshot of the spreadsheet of branch circuit calculations that I performed to figure out wire sizes.

The actual spreadsheet can be found  by clicking here.

As can be seen from the spreadsheet I am planning to use 24 volts DC allowing for at most a 2% voltage drop.  I assumed that my light loads would not exceed 13 watts per installed light fixture (which I believe is much more than I will need with LED’s) and I allowed extra capacity on the circuits for items like ceiling fans.  Finally, I was very conservative when estimating the actual length of my branch circuits.

This led me to install mostly 12 gauge and some 10 gauge wire for these circuits … an initial extra cost that will hopefully pay off down the road.

Some of the outstanding questions that I still have:

  • Can I install my smoke detectors on a DC branch circuit?  There are a few issues here; are DC detectors built like AC detectors, will the inspector have any problems with this?  My initial thought is that it makes the most sense to install the detectors on DC branch circuits, but I am still learning and investigating.
  • What style of plugs do I use for DC plugin receptacles?  Obviously, they need to be distinct from AC plugins, but is there any standard here?

The two most useful resources I have found while working on all of this are:

  • Photovoltaics: Design and Installation Manual (By Solar Energy International?)
  • Electrical Codes Simplified (by P.S. Knight)

I think my next step in the electrical is to go back to the distribution panel and start figuring out the DC side of the system …


Electrical Rough-In Wiring of Earthship Tire Walls

It has been a few days since we finished our rough-in wiring, but I thought I would post about it before I forget the details.

As mentioned previously we spent some time after getting our electrical permit figuring out what type of wire would be required for the tire walls; the electrical inspector initially wanted us to use metallic or non-metallic conduit to protect against corrosion and moisture.  Based on our research of other buildings of cob construction in British Columbia we were able to show the building inspector that standard wiring and boxes have been used in buildings with similar construction techniques.

Last week we finally started the rough-in wiring of the tire walls.  I started working on the ends of the interior tire walls; we have wire running in channels at the tops of these walls and there will be switch outlets on the ends of all of these walls.  We decided to frame a wiring chase on the end of every wall rather than cob over this wiring.  There were two reasons for this choice; I was worried that there would not be a lot of cob covering the wire runs on the ends of the walls, and we intend to finish these chases so that they look like posts at the ends of the interior walls  … we hope that it will be aesthetically pleasing.  Making these boxes was slow work as the 2×6 forming the box had to be custom fit to the tire stack.  Eventually we will cob over the custom edges of the 2×6 when we finish mudding the walls.

On each of the end walls I put a 3 or 4 gang electrical box approximately 4′ above finished floor height.  These boxes will hold the light switches for the main room lights.  The intention is for all of the lighting circuits to be on DC power.  I ran some of these branch circuits using #10 AWG wire due to the length of the runs and number of lights on the circuit; I did not want any issues with voltage drop due to insufficient wire sizes.  I also placed a single gang box approximately 1′ above finished floor level in these chases.  This allows me to have a DC plugin in every room, something I was not sure how I was going to accomplish otherwise.  I did not include these DC plugins when ensuring that there was no point along the wall of the room further than 12′ from an electrical outlet; I ensured that you are always within 12′ of an AC plugin.

Once these end wall chases were finished we moved on to the wiring beside the east and west exterior doorways.  Here again electrical wiring for room lights travelled in a channel at the top of the tire wall.  This wiring was brought down to approximately 4′ above finished grade into a switch receptacle gang box by running it in the recessed grooves between the tires. The wires were attached to the tires using 3/4″ screws and CSA approved wire clips.  Here again, a single gang plugin was placed underneath the switch box.

Finally, all of the branch circuits were run for the plug receptacles on the tire walls.  All of these gang boxes were mounted on plywood screwed over the cavity between two tires in the wall.  A box was cut out of the plywood using a jigsaw and the gang box was mounted and screwed to the plywood.  Before mounting the gang box 6 mil poly and stucco lathe was stapled over the exposed face of the plywood.  The lathe extends beyond the edges of the plywood.  As described above the electrical wire was stapled in the cavities formed between the tires.

We passed the wire between rooms by drilling through the cob packed between the tires.  This worked well and reduced the wire runs as we did not have to go right out to the end of each wall.  We made sure the wire was stapled within 6″ of entering a gang box and at least every 5′ feet along its length.  At least 6″ of conductor was run into the gang boxes.

All of this work took two of us three days.