The important evolution of the Arc is the curved roof on the curved plan. The south wall also curves back one foot from bottom to top, softening it further and creating contrast to the rectilinear element which is now subservient and punches through the curve, readjusting the angle on the end to maximize solar collection. Roof water is now being collected in several places where it can easily be stored and used for flushing toilets, laundry, and growing food. The west end of the arc is higher than necessary and the skylights in the center are problematic for summer overheating, although summer venting will be powered by a west-facing, solar-thermal collector on the chimney. Small wall-washing skylights on the north of the roof will be replaced by south-facing monitors with mirrors, basically a vertical glazed extension of the wall. This will add to winter but not summer heat gain and bring diffused light to the north of the main space. The location of a large amount of photovoltaics is yet unclear in this scheme.

It was decided that the octagonal schemes were too competitive in scale with the main house, and that a more linear addition, maximizing the south face of the knoll, as well as an element providing western views, would work better and fit into the existing bare spots on the site. Conceptually these forms would be generated by the dome playing against the rectilinear elements and using the original color scheme to differentiate the two. A side benefit would be small semi-defined "courtyard" spaces between the pieces.
Below a set of variations of this idea were explored. A presentation was submitted to the design committee of the development for a conceptual approval. The digital model was shown with abstracted trees, and photo-montages of the model overlaid on photos taken of the site were made for the committee to see what the project would look like from the public road.

One design issues can be seen in these photos: how does the rectilinear element intersect with the radial element? In this first scheme both collide in a lantern over the cross-axis. Half of the surfaces are devoted to each element and are topped by a south facing monitor. Later this resolution was rethought.

In this scheme the design of the greenhouse and ceramics studio was determined. The greenhouse provides additional warm air for the main house and acts as a passage to the dining roof deck. On the south wall of the studio the 3 window/door bays are part direct gain, part active collector, the hot air being drawn down to a thermal storage bed under the slab. A portion of this sub-slab bed is devoted to air from the kiln room where waste heat is retrieved and stored for later space heating. A construction detail of this bed is shown to the left. Above are the diagrammatic structure of the studio and a preliminary sketch of the sub-slab bed plan.

Here are some of the intermediate versions of the Arc schemes for the art studio/guest house/and growing greenhouse. As the interior plans evolved, exterior forms changed. All explore the use of direct gain and air collectors for heat storage.