Casco Bay Residence is a highly energy-efficient, 1800 square foot, Y-shaped residence built on the existing footprint of the original home. Specific zoning regulations allowed for a 30% expansion of the existing structure, which was effectively utilized to improve the insulation values of the walls and ceiling, as the thickness of the new walls and ceilings required that area to maintain the existing usable floor area. Passive solar gain and triple-pane windows enhance the energy efficient qualities of the building.