One major concern was cost, of course. But besides that it was how a particular floor plan would work in terms of the thermal envelope. I already mentioned that we dropped the cathedral ceiling idea because of energy aspects, but there is more. One fundamental principle is to reduce wall space. From basic geometry, we know that the best perimeter to area ratio is offered by a circle. Since a round house is not our preferred solution and it would be impractical to build, the next best thing is a square. Non-square rectangles are already less optimal, and every corner, every wing or addition makes a house less energy efficient due to the increased wall space. So a basic rectangular footprint (as close to square as possible) should be the target for any energy efficient house. External additions that are not in the thermal envelope like garages, porches etc. are OK though. When talking about the horizontal thermal insulation, window area (and window types) is another topic. But I will save that for later.
The next step is the in the thermal insulation towards the roof. While there are methods of properly insulating the roof itself (when using attic space or having a second floor like in a cape style house with at least partial slanted ceilings), it adds cost and the need for spray foam or other non-recycled material.
Avoiding the use of the attic all together allows for simply putting many inches of loosely packed cellulose on top of your (flat) ceiling of the main or upper floor. That is basically what we did in yet another evolution step: Instead of adding guest quarters and office space under the roof, we moved these rooms into the basement. After some cost discussions, we even decided against finishing the space under the roof in the future, so that a simple truss design can be used.
Here's the status of May 2013 (actually, one of the many options under investigation; this particular one was using s straight staircase to the lower floor):
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| Main Floor (May 2013) |
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| Basement (May 2013) |
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| West Elevation (May 2013) |
