That's a pricey list of not includeds and notice they say nothing here and I saw nothing in my quick scan of the site about some really big and typical costs like excavation and foundations, below grade walls, or basement floor. They say this is a structural package but they don't mention all the things that are going to be extra that most people would expect in a house - plumbing, wiring, fixtures (electrical and plumbing), stove, etc. and especially that the solar PV and thermal water heating systems are not part of the package. It would be nice if they said right up front and clearly what they do and don't sell. And they should make it very clear that all the prices include only the factory labor, not the cost of actually assembling and finishing these structures.

But the biggest issue I have is that these are essentially double wall structures using an enormous amount of thick, milled lumber, which appears to use many times more wood than goes into a stick frame house. It would be interesting to see if they use more wood than a comparable log home. They'll likely be more energy efficient than a log home, but they'll use as much or more wood. Which raises all sorts of issues about the sustainability of this venture - beyond just the trees cut down - much bigger transportation, milling, probably kiln drying impacts as well. The concept is fine and likely works reasonably well in most climates. I'd need to see much more actual performance data and of course real cost data to be able to make any kind of realistic judgment of the viability of this concept as anything more than a niche market system. But between the costs which are going to be very high and the amount of materials going into one of these, calling it sustainable seems like a real stretch."

And finally, Jeff Judkoff of the National Renewable Energy Laboratory, wrote: "The concept of "Double Envelope" homes has been around since at least the 1970's. A number of them were built in the late 70's early 80's. Some variations of the concept were published in the Solar Home Book, by Bruce Anderson and Michael Riordan in 1976, Cheshire Books. Other publications in that time frame also showed the concept. The only truly new concept here is the notion that the resins in the wood behave as phase change storage materials. I have no idea if that is true, but I doubt it because the most common phase change is from a solid to a liquid, in which case the resins in their liquid phase would leak out creating a mess. That's not to rule out the possibility that some tree resins could go from a solid to semi-solid phase, or that they are encapsulated in the wood, I just don't know if they can, and would only be able to determine it through controlled scientific testing in a calorimetry chamber. Phase change storage can really be a big boost to the performance of many flavors of passively heated and cooled homes.

There are many ways to acheive highly efficient homes that more or less "heat and cool" themselves. Different approaches have different costs and will work better in some climates than in others. In Colorado, my lab, NREL, worked with Habitat for Humanity to create a net energy producing home. We used super insulation, passive solar tempering, ventilation heat recovery, engineered shading, solar hot water with a backup instantaneous water heater, compact flourescent lighting, and PV. We also have more than a years worth of detailed data to prove the performance of the home (it really was a net energy producer for the last year).

I saw no data to indicate how well the Enertia home actually performed from an energy perspective. Cost, energy performance, and comfort are the key criteria by which to evaluate such homes, and data is always better than arm waving, or catchy theories. Nothing beats the scientific method for objectively determining the value of an idea."

Alvaro Ramírez y Clarisa Elton

House in Buchupureo

Cliffhanger - Alvaro Ramírez and Clarisa Elton - are the authors of their own weekend retreat on the central Chile coastline. Great residential design, propped on stilts, with minimal environmental impact.