A few questions on the packaged or Global earthship design

I'm beginning the process of really starting to get informed about the details about what would be involved in building an earthship and wanted to clear up two questions i had.

1. in the global earthship, what is the thickness of the foam board used to insulate the earth around the tires outside the home.

2. My build site has no well and I'd love to be able to catch all our water using the roof. The part that doesn't make sense is the math. Mike stated in a video that the earthships they built at their site could gather plenty of water to support the family size on their 7-8" of water per year. He also stated that the water guy in their county figured that the average american uses 90 gallons per day but due to the recycling of water in an earthship they only used 19 gallons per person per day. In a place of 8" of water per day that means for each family member there needs to be 1486sqft of roof! For my family of 4 it would require a 6000sqft house in an area of 8". Math doesn't add up, very possible i'm figuring something wrong but i wanted to check in with you guys. In my case i live in a place with around 13" of rain and a few feet of snow per year (so maybe another 2 inches max), but still math doesn't add up, at 15" of precipitation we're looking at a bare minimum of 3200sqft of roof space for a family of four assuming we get the full 15" every year? just seems excessive.

Well that's all for now. Truth is i have tons of questions but figure I'd ease into it. The jist of my idea is to build an earthship type house but using ecology blocks instead of tires (to save on time and labor as I'm self employed and every hour i spend on the house is an hour i spend not earning a living). I live in North central washington at 4000ft where temps drop down belowing freezing all winter and only go up to around 80F during the heat of summer.

Each board of insul is 2" and Reynolds recommends 4" total.
Mike exaggerates a lot. I have worked with him on a build in Montana. While genius also eccentric. Members of his crew who live in Earthships openly tell us they have water hauled to their house twice a year, Or depending on the size of their family. The point Reynolds is making is the approach to self sustaininablity and self containment. But he makes it sound like it's been achieved by the earthships in Taos. It's not. Just closer than most Americans. At least water isn't pumped to their house everyday by the city! It's a starting point. Now watch the movie, Garbage Warrior. He says in the movie " A family of four could totally survive in this house without going to the grocery store." (paraphrase) He later put out YouTube videos of him and some of their crew trying to do just that. Not pretty.
Just the same, combine permaculture concepts and Earthship concepts and it will be hard to fail.
My wife and I are building ours out of pocket while working full time. We would love to form an alliance of information. Have a great day!
Kyle and Erin

Erin, you are in Lander? Do you know my uncle Ralph Allen? His family (now 3 generations) have lived there for as long as I can remember.

I agree that a lot of the "math" doesn't add up. That doesn't mean that it is unfeasible, however. Earthships simply must be built fairly large to be self-sufficient, and they will never be self-sufficient for food, something any builder of an Earthship must understand. 3200 square feet of roof may sound big, but how big is that really? Let's do some quick numbers.

The living space inside the Earthship is only a part of the roof. Let's say a family of four needs a conservative 1500 square feet of living area. This could be 75 feet wide by 20 feet deep. Now using the recommended form factor for the greenhouse, you would need an additional 10 feet of greenhouse in front of your living area. Now the cisterns. After accounting for the depth of the cisterns, the insulation and berming, and if you were to put the "drain" into the cistern as far back as possible, (not forgetting that the Global design cisterns are too small and will need to be amped up), you have about another 10 feet of roof space.

Adding an overhang of 2 feet, a slope of 7 degrees, and you now have a roof area of 3173 square feet. It is feasible, you just have to eek out every square foot of your roof that you can. Now, if you live in a rainy area, it is easier.

Check with your local building department, regarding the feasibility of the Global design. I don't think it would be permitted in Colorado. I built a tire-bale earthship, in the older conventional earthship style, and they were real sticklers about bedroom fire egresses. In El Paso county, Colorado, for Earthship designs, they require that the bedrooms be on the ends, where the doors are considered egresses. In a conventional home, the bedroom windows are considered the egresses, but in most Earthship designs (including the Global), there are no windows in the bedrooms. Even though everything is somewhat open, the bedrooms had to be on the ends. Of course, once we got our OP, we moved them